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Yaeger LN, Ranieri MRM, Chee J, Karabelas-Pittman S, Rudolph M, Giovannoni AM, Harvey H, Burrows LL. A genetic screen identifies a role for oprF in Pseudomonas aeruginosa biofilm stimulation by subinhibitory antibiotics. NPJ Biofilms Microbiomes 2024; 10:30. [PMID: 38521769 PMCID: PMC10960818 DOI: 10.1038/s41522-024-00496-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Accepted: 03/05/2024] [Indexed: 03/25/2024] Open
Abstract
Biofilms are surface-associated communities of bacteria that grow in a self-produced matrix of polysaccharides, proteins, and extracellular DNA (eDNA). Sub-minimal inhibitory concentrations (sub-MIC) of antibiotics induce biofilm formation, potentially as a defensive response to antibiotic stress. However, the mechanisms behind sub-MIC antibiotic-induced biofilm formation are unclear. We show that treatment of Pseudomonas aeruginosa with multiple classes of sub-MIC antibiotics with distinct targets induces biofilm formation. Further, addition of exogenous eDNA or cell lysate failed to increase biofilm formation to the same extent as antibiotics, suggesting that the release of cellular contents by antibiotic-driven bacteriolysis is insufficient. Using a genetic screen for stimulation-deficient mutants, we identified the outer membrane porin OprF and the ECF sigma factor SigX as important. Similarly, loss of OmpA - the Escherichia coli OprF homolog - prevented sub-MIC antibiotic stimulation of E. coli biofilms. Our screen also identified the periplasmic disulfide bond-forming enzyme DsbA and a predicted cyclic-di-GMP phosphodiesterase encoded by PA2200 as essential for biofilm stimulation. The phosphodiesterase activity of PA2200 is likely controlled by a disulfide bond in its regulatory domain, and folding of OprF is influenced by disulfide bond formation, connecting the mutant phenotypes. Addition of reducing agent dithiothreitol prevented sub-MIC antibiotic biofilm stimulation. Finally, activation of a c-di-GMP-responsive promoter follows treatment with sub-MIC antibiotics in the wild-type but not an oprF mutant. Together, these results show that antibiotic-induced biofilm formation is likely driven by a signaling pathway that translates changes in periplasmic redox state into elevated biofilm formation through increases in c-di-GMP.
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Affiliation(s)
- Luke N Yaeger
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada
| | - Michael R M Ranieri
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada
| | - Jessica Chee
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada
| | - Sawyer Karabelas-Pittman
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada
| | - Madeleine Rudolph
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada
| | - Alessio M Giovannoni
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada
| | - Hanjeong Harvey
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada
| | - Lori L Burrows
- Biochemistry and Biomedical Sciences and the Michael G. DeGroote Centre for Infectious Disease Research, McMaster University, Hamilton, ON, Canada.
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2
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Yin F, Hu Y, Bu Z, Liu Y, Zhang H, Hu Y, Xue Y, Li S, Tan C, Chen X, Li L, Zhou R, Huang Q. Genome-wide identification of genes critical for in vivo fitness of multi-drug resistant porcine extraintestinal pathogenic Escherichia coli by transposon-directed insertion site sequencing using a mouse infection model. Virulence 2023; 14:2158708. [PMID: 36537189 PMCID: PMC9828833 DOI: 10.1080/21505594.2022.2158708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Extraintestinal pathogenic Escherichia coli (ExPEC) is an important zoonotic pathogen. Recently, ExPEC has been reported to be an emerging problem in pig farming. However, the mechanism of pathogenicity of porcine ExPEC remains to be revealed. In this study, we constructed a transposon (Tn) mutagenesis library covering Tn insertion in over 72% of the chromosome-encoded genes of a virulent and multi-drug resistant porcine ExPEC strain PCN033. By using a mouse infection model, a transposon-directed insertion site sequencing (TraDIS) assay was performed to identify in vivo fitness factors. By comparing the Tn insertion frequencies between the input Tn library and the recovered library from different organs, 64 genes were identified to be involved in fitness during systemic infection. 15 genes were selected and individual gene deletion mutants were constructed. The in vivo fitness was evaluated by using a competitive infection assay. Among them, ΔfimG was significantly outcompeted by the WT strain in vivo and showed defective adhesion to host cells. rfa which was involved in lipopolysaccharide biosynthesis was shown to be critical for in vivo fitness which may have resulted from its role in the resistance to serum killing. In addition, several metabolic genes including fepB, sdhC, fepG, gltS, dcuA, ccmH, ddpD, narU, glpD, malM, and yabL and two regulatory genes metJ and baeS were shown as important determinants of in vivo fitness of porcine ExPEC. Collectively, this study performed a genome-wide screening for in vivo fitness factors which will be important for understanding the pathogenicity of porcine ExPEC.
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Affiliation(s)
- Fan Yin
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China
| | - Yan Hu
- College of Animal Sciences & Technology, Huazhong Agricultural University, Wuhan, China
| | - Zixuan Bu
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China
| | - Yuying Liu
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China
| | - Hui Zhang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China
| | - Yawen Hu
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China
| | - Ying Xue
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China
| | - Shaowen Li
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China
| | - Chen Tan
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Ministry of Science and Technology, International Research Center for Animal Disease, Wuhan, China
| | - Xiabing Chen
- Institute of Animal Husbandry and Veterinary Science, Wuhan Academy of Agricultural Science and Technology, Wuhan, China
| | - Lu Li
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Ministry of Science and Technology, International Research Center for Animal Disease, Wuhan, China
| | - Rui Zhou
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Ministry of Science and Technology, International Research Center for Animal Disease, Wuhan, China,The HZAU-HVSEN Institute, Wuhan, China,CONTACT Rui Zhou
| | - Qi Huang
- State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Cooperative Innovation Center for Sustainable Pig Production, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China,Ministry of Science and Technology, International Research Center for Animal Disease, Wuhan, China,Qi Huang
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3
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Huijboom L, Tempelaars M, Fan M, Zhu Y, Boeren S, van der Linden E, Abee T. l-tyrosine modulates biofilm formation of Bacillus cereus ATCC 14579. Res Microbiol 2023; 174:104072. [PMID: 37080258 DOI: 10.1016/j.resmic.2023.104072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2022] [Revised: 04/11/2023] [Accepted: 04/12/2023] [Indexed: 04/22/2023]
Abstract
Bacillus cereus is a food-borne pathogen capable of producing biofilms. Following analysis of biofilm formation by B. cereus ATCC 14579 transposon mutants in defined medium (DM), a deletion mutant of bc2939 (Δbc2939) was constructed that showed decreased crystal violet biofilm staining and biofilm cell counts. In addition, Δbc2939 also produced smaller colony biofilms with lower cell counts and loss of wrinkly morphology. The bc2939 gene encodes for Prephenate dehydrogenase, which converts Prephenate to 4-Hydroxy-phenylpyruvate (4-HPPA) in the l-tyrosine branch of the Shikimate pathway. While growth of the mutant and WT in DM was similar, addition of l-tyrosine was required to restore WT-like (colony) biofilm formation. Comparative proteomics showed reduced expression of Tyrosine-protein kinase/phosphatase regulators and extracellular polysaccharide cluster 1 (EPS1) proteins, aerobic electron transfer chain cytochrome aa3/d quinol oxidases, and iso-chorismate synthase involved in menaquinone synthesis in DM grown mutant biofilm cells, while multiple oxidative stress-related catalases and superoxide dismutases were upregulated. Performance in shaking cultures showed a 100-fold lower concentration of menaquinone-7 and reduction in cell counts of DM grown Δbc2939 indicating increased oxygen sensitivity. Combining all results, points to an important role of Tyrosine-modulated EPS1 production and menaquinone-dependent aerobic respiration in B. cereus ATCC 14579 (colony) biofilm formation.
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Affiliation(s)
- Linda Huijboom
- Food Microbiology, Wageningen University & Research, Bornse Weilanden 9, 6708, WG, Wageningen, the Netherlands.
| | - Marcel Tempelaars
- Food Microbiology, Wageningen University & Research, Bornse Weilanden 9, 6708, WG, Wageningen, the Netherlands.
| | - Mingzhen Fan
- Food Microbiology, Wageningen University & Research, Bornse Weilanden 9, 6708, WG, Wageningen, the Netherlands.
| | - Yourong Zhu
- Food Microbiology, Wageningen University & Research, Bornse Weilanden 9, 6708, WG, Wageningen, the Netherlands.
| | - Sjef Boeren
- Laboratory of Biochemistry, Wageningen University & Research, Stippeneng 4, Wageningen, 6708, WE, the Netherlands.
| | - Erik van der Linden
- Laboratory of Physics and Physical Chemistry of Foods, Wageningen University & Research, Bornse Weilanden 9, 6708, WG, Wageningen, the Netherlands.
| | - Tjakko Abee
- Food Microbiology, Wageningen University & Research, Bornse Weilanden 9, 6708, WG, Wageningen, the Netherlands.
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Mwenda GM, Hill YJ, O’Hara GW, Reeve WG, Howieson JG, Terpolilli JJ. Competition in the Phaseolus vulgaris- Rhizobium symbiosis and the role of resident soil rhizobia in determining the outcomes of inoculation. PLANT AND SOIL 2023; 487:61-77. [PMID: 37333056 PMCID: PMC10272266 DOI: 10.1007/s11104-023-05903-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Accepted: 01/24/2023] [Indexed: 06/20/2023]
Abstract
Background and Aims Inoculation of legumes with effective N2-fixing rhizobia is a common practice to improve farming profitability and sustainability. To succeed, inoculant rhizobia must overcome competition for nodulation by resident soil rhizobia that fix N2 ineffectively. In Kenya, where Phaseolus vulgaris (common bean) is inoculated with highly effective Rhizobium tropici CIAT899 from Colombia, response to inoculation is low, possibly due to competition from ineffective resident soil rhizobia. Here, we evaluate the competitiveness of CIAT899 against diverse rhizobia isolated from cultivated Kenyan P. vulgaris. Methods The ability of 28 Kenyan P. vulgaris strains to nodulate this host when co-inoculated with CIAT899 was assessed. Rhizosphere competence of a subset of strains and the ability of seed inoculated CIAT899 to nodulate P. vulgaris when sown into soil with pre-existing populations of rhizobia was analyzed. Results Competitiveness varied widely, with only 27% of the test strains more competitive than CIAT899 at nodulating P. vulgaris. While competitiveness did not correlate with symbiotic effectiveness, five strains were competitive against CIAT899 and symbiotically effective. In contrast, rhizosphere competence strongly correlated with competitiveness. Soil rhizobia had a position-dependent numerical advantage, outcompeting seed-inoculated CIAT899 for nodulation of P. vulgaris, unless the resident strain was poorly competitive. Conclusion Suboptimally effective rhizobia can outcompete CIAT899 for nodulation of P. vulgaris. If these strains are widespread in Kenyan soils, they may largely explain the poor response to inoculation. The five competitive and effective strains characterized here are candidates for inoculant development and may prove better adapted to Kenyan conditions than CIAT899.
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Affiliation(s)
- George M. Mwenda
- Legume Rhizobium Sciences, Food Futures Institute, Murdoch University, 90 South Street, Murdoch, WA 6150 Australia
- Present Address: Department of Primary Industries and Regional Development, 75 York Road, Northam, WA 6401 Australia
| | - Yvette J. Hill
- Legume Rhizobium Sciences, Food Futures Institute, Murdoch University, 90 South Street, Murdoch, WA 6150 Australia
| | - Graham W. O’Hara
- Legume Rhizobium Sciences, Food Futures Institute, Murdoch University, 90 South Street, Murdoch, WA 6150 Australia
| | - Wayne G. Reeve
- Food Futures Institute, Murdoch University, 90 South Street, Murdoch, WA 6150 Australia
| | - John G. Howieson
- Legume Rhizobium Sciences, Food Futures Institute, Murdoch University, 90 South Street, Murdoch, WA 6150 Australia
| | - Jason J. Terpolilli
- Legume Rhizobium Sciences, Food Futures Institute, Murdoch University, 90 South Street, Murdoch, WA 6150 Australia
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5
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inPOSE: A Flexible Toolbox for Chromosomal Cloning and Amplification of Bacterial Transgenes. Microorganisms 2022; 10:microorganisms10020236. [PMID: 35208691 PMCID: PMC8875745 DOI: 10.3390/microorganisms10020236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 01/14/2022] [Accepted: 01/18/2022] [Indexed: 12/10/2022] Open
Abstract
Cloning the genes and operons encoding heterologous functions in bacterial hosts is now almost exclusively carried out using plasmid vectors. This has multiple drawbacks, including the need for constant selection and variation in copy numbers. The chromosomal integration of transgenes has always offered a viable alternative; however, to date, it has been of limited use due to its tedious nature and often being limited to a single copy. We introduce here a strategy that uses bacterial insertion sequences, which are the simplest autonomous transposable elements to insert and amplify genetic cargo into a bacterial chromosome. Transgene insertion can take place either as transposition or homologous recombination, and copy number amplification is achieved using controlled copy-paste transposition. We display the successful use of IS1 and IS3 for this purpose in Escherichia coli cells using various selection markers. We demonstrate the insertion of selectable genes, an unselectable gene and a five-gene operon in up to two copies in a single step. We continue with the amplification of the inserted cassette to double-digit copy numbers within two rounds of transposase induction and selection. Finally, we analyze the stability of the cloned genetic constructs in the lack of selection and find it to be superior to all investigated plasmid-based systems. Due to the ubiquitous nature of transposable elements, we believe that with proper design, this strategy can be adapted to numerous other bacterial species.
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6
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Vu HN, Subuyuj GA, Crisostomo RV, Skovran E. Transposon mutagenesis for methylotrophic bacteria using Methylorubrum extorquens AM1 as a model system. Methods Enzymol 2021; 650:159-184. [PMID: 33867020 DOI: 10.1016/bs.mie.2021.01.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Transposon mutagenesis utilizes transposable genetic elements that integrate into a recipient genome to generate random insertion mutations which are easily identified. This forward genetic approach has proven powerful in elucidating complex processes, such as various pathways in methylotrophy. In the past decade, many methylotrophic bacteria have been shown to possess alcohol dehydrogenase enzymes that use lanthanides (Lns) as cofactors. Using Methylorubrum extorquens AM1 as a model organism, we discuss the experimental designs, protocols, and results of three transposon mutagenesis studies to identify genes involved in different aspects of Ln-dependent methanol oxidation. These studies include a selection for transposon insertions that prevent toxic intracellular formaldehyde accumulation, a fluorescence-imaging screen to identify regulatory processes for a primary Ln-dependent methanol dehydrogenase, and a phenotypic screen for genes necessary for function of a Ln-dependent ethanol dehydrogenase. We anticipate that the methods described in this chapter can be applied to understand other metabolic systems in diverse bacteria.
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Affiliation(s)
- Huong N Vu
- Department of Biological Sciences, San José State University, San José, CA, United States
| | - Gabriel A Subuyuj
- Department of Biological Sciences, San José State University, San José, CA, United States
| | | | - Elizabeth Skovran
- Department of Biological Sciences, San José State University, San José, CA, United States.
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7
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Fujiwara K, Katagi Y, Ito K, Chiba S. Proteome-wide Capture of Co-translational Protein Dynamics in Bacillus subtilis Using TnDR, a Transposable Protein-Dynamics Reporter. Cell Rep 2020; 33:108250. [DOI: 10.1016/j.celrep.2020.108250] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 09/03/2020] [Accepted: 09/17/2020] [Indexed: 11/29/2022] Open
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Generation of Random luxCDABE Transcriptional Fusions in the Genome of Salmonella enterica. Methods Mol Biol 2020. [PMID: 32894493 DOI: 10.1007/978-1-0716-0791-6_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
The luxCDABE operon of Photorhabdus luminescens can be used as a bioluminescent reporter to measure gene transcription nondestructively. Here we describe protocols to (1) generate random transcriptional fusions of the lux operon to genes of the Salmonella genome, (2) screen for specific fusions with constitutive expression, Salmonella pathogenicity island 1-related expression, or Salmonella pathogenicity island 2-related expression, and (3) determine the site of luxCDABE integration.
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9
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Envelope Stress and Regulation of the Salmonella Pathogenicity Island 1 Type III Secretion System. J Bacteriol 2020; 202:JB.00272-20. [PMID: 32571967 DOI: 10.1128/jb.00272-20] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 06/15/2020] [Indexed: 01/19/2023] Open
Abstract
Salmonella enterica serovar Typhimurium uses a type three secretion system (T3SS) encoded on the Salmonella pathogenicity island 1 (SPI1) to invade intestinal epithelial cells and induce inflammatory diarrhea. The SPI1 T3SS is regulated by numerous environmental and physiological signals, integrated to either activate or repress invasion. Transcription of hilA, encoding the transcriptional activator of the SPI1 structural genes, is activated by three AraC-like regulators, HilD, HilC, and RtsA, that act in a complex feed-forward loop. Deletion of bamB, encoding a component of the β-barrel assembly machinery, causes a dramatic repression of SPI1, but the mechanism was unknown. Here, we show that partially defective β-barrel assembly activates the RcsCDB regulon, leading to decreased hilA transcription. This regulation is independent of RpoE activation. Though Rcs has been previously shown to repress SPI1 when disulfide bond formation is impaired, we show that activation of Rcs in a bamB background is dependent on the sensor protein RcsF, whereas disulfide bond status is sensed independently. Rcs decreases transcription of the flagellar regulon, including fliZ, the product of which indirectly activates HilD protein activity. Rcs also represses hilD, hilC, and rtsA promoters by an unknown mechanism. Both dsbA and bamB mutants have motility defects, though this is simply regulatory in a bamB background; motility is restored in the absence of Rcs. Effector secretion assays show that repression of SPI1 in a bamB background is also regulatory; if expressed, the SPI1 T3SS is functional in a bamB background. This emphasizes the sensitivity of SPI1 regulation to overall envelope homeostasis.IMPORTANCE Salmonella causes worldwide foodborne illness, leading to massive disease burden and an estimated 600,000 deaths per year. Salmonella infects orally and invades intestinal epithelial cells using a type 3 secretion system that directly injects effector proteins into host cells. This first step in invasion is tightly regulated by a variety of inputs. In this work, we demonstrate that Salmonella senses the functionality of outer membrane assembly in determining regulation of invasion machinery, and we show that Salmonella uses distinct mechanisms to detect specific perturbations in envelope assembly.
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Salvail H, Groisman EA. The phosphorelay BarA/SirA activates the non-cognate regulator RcsB in Salmonella enterica. PLoS Genet 2020; 16:e1008722. [PMID: 32392214 PMCID: PMC7241856 DOI: 10.1371/journal.pgen.1008722] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 05/21/2020] [Accepted: 03/18/2020] [Indexed: 11/18/2022] Open
Abstract
To survive an environmental stress, organisms must detect the stress and mount an appropriate response. One way that bacteria do so is by phosphorelay systems that respond to a stress by activating a regulator that modifies gene expression. To ensure an appropriate response, a given regulator is typically activated solely by its cognate phosphorelay protein(s). However, we now report that the regulator RcsB is activated by both cognate and non-cognate phosphorelay proteins, depending on the condition experienced by the bacterium Salmonella enterica serovar Typhimurium. The RcsC and RcsD proteins form a phosphorelay that activates their cognate regulator RcsB in response to outer membrane stress and cell wall perturbations, conditions Salmonella experiences during infection. Surprisingly, the non-cognate phosphorelay protein BarA activates RcsB during logarithmic growth in Luria-Bertani medium in three ways. That is, BarA’s cognate regulator SirA promotes transcription of the rcsDB operon; the SirA-dependent regulatory RNAs CsrB and CsrC further increase RcsB-activated gene transcription; and BarA activates RcsB independently of the RcsC, RcsD, and SirA proteins. Activation of a regulator by multiple sensors broadens the spectrum of environments in which a set of genes is expressed without evolving binding sites for different regulators at each of these genes. The phosphorelay is a form of signal transduction used by organisms in all three domains of life. Typically, a phosphorelay consists of sensor proteins that respond to specific signals by activating a cognate regulatory protein that alters gene expression. Phosphorelays exhibit specificity towards their cognate regulators, thereby ensuring that any changes in gene expression help an organism cope with the experienced stress (and not with an unrelated stress). However, we now report that the regulator RcsB is activated by both cognate and non-cognate phosphorelay proteins in the bacterium Salmonella enterica serovar Typhimurium. The phosphorelay proteins RcsC and RcsD activate RcsB upon cell envelope perturbations, whereas the non-cognate phosphorelay protein BarA activates RcsB during rapid growth in Luria-Bertani medium. Our findings establish that BarA controls gene expression via both its cognate regulator SirA and the non-cognate regulator RcsB. In addition, they demonstrate that RcsB controls gene expression in response to multiple signals detected by the RcsC, RcsD, and BarA proteins.
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Affiliation(s)
- Hubert Salvail
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, United States of America
- Yale Microbial Sciences Institute, West Haven, Connecticut, United States of America
| | - Eduardo A. Groisman
- Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut, United States of America
- Yale Microbial Sciences Institute, West Haven, Connecticut, United States of America
- * E-mail:
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11
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Bekebrede H, Lin M, Teymournejad O, Rikihisa Y. Discovery of in vivo Virulence Genes of Obligatory Intracellular Bacteria by Random Mutagenesis. Front Cell Infect Microbiol 2020; 10:2. [PMID: 32117791 PMCID: PMC7010607 DOI: 10.3389/fcimb.2020.00002] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 01/06/2020] [Indexed: 11/13/2022] Open
Abstract
Ehrlichia spp. are emerging tick-borne obligatory intracellular bacteria that cause febrile and sometimes fatal diseases with abnormal blood cell counts and signs of hepatitis. Ehrlichia HF strain provides an excellent mouse disease model of fatal human ehrlichiosis. We recently obtained and established stable culture of Ehrlichia HF strain in DH82 canine macrophage cell line, and obtained its whole genome sequence and annotation. To identify genes required for in vivo virulence of Ehrlichia, we constructed random insertional HF strain mutants by using Himar1 transposon-based mutagenesis procedure. Of total 158 insertional mutants isolated via antibiotic selection in DH82 cells, 74 insertions were in the coding regions of 55 distinct protein-coding genes, including TRP120 and multi-copy genes, such as p28/omp-1, virB2, and virB6. Among 84 insertions mapped within the non-coding regions, seven are located in the putative promoter region since they were within 50 bp upstream of the seven distinct genes. Using limited dilution methods, nine stable clonal mutants that had no apparent defect for multiplication in DH82 cells, were obtained. Mouse virulence of seven mutant clones was similar to that of wild-type HF strain, whereas two mutant clones showed significantly retarded growth in blood, livers, and spleens, and the mice inoculated with them lived longer than mice inoculated with wild-type. The two clones contained mutations in genes encoding a conserved hypothetical protein and a staphylococcal superantigen-like domain protein, respectively, and both genes are conserved among Ehrlichia spp., but lack homology to other bacterial genes. Inflammatory cytokine mRNA levels in the liver of mice infected with the two mutants were significantly diminished than those infected with HF strain wild-type, except IL-1β and IL-12 p40 in one clone. Thus, we identified two Ehrlichia virulence genes responsible for in vivo infection, but not for infection and growth in macrophages.
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Affiliation(s)
| | | | | | - Yasuko Rikihisa
- Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH, United States
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12
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Conceptual Model of Biofilm Antibiotic Tolerance That Integrates Phenomena of Diffusion, Metabolism, Gene Expression, and Physiology. J Bacteriol 2019; 201:JB.00307-19. [PMID: 31501280 DOI: 10.1128/jb.00307-19] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Accepted: 08/28/2019] [Indexed: 01/14/2023] Open
Abstract
Transcriptomic, metabolomic, physiological, and computational modeling approaches were integrated to gain insight into the mechanisms of antibiotic tolerance in an in vitro biofilm system. Pseudomonas aeruginosa biofilms were grown in drip flow reactors on a medium composed to mimic the exudate from a chronic wound. After 4 days, the biofilm was 114 μm thick with 9.45 log10 CFU cm-2 These biofilms exhibited tolerance, relative to exponential-phase planktonic cells, to subsequent treatment with ciprofloxacin. The specific growth rate of the biofilm was estimated via elemental balances to be approximately 0.37 h-1 and with a reaction-diffusion model to be 0.32 h-1, or one-third of the maximum specific growth rate for planktonic cells. Global analysis of gene expression indicated lower transcription of ribosomal genes and genes for other anabolic functions in biofilms than in exponential-phase planktonic cells and revealed the induction of multiple stress responses in biofilm cells, including those associated with growth arrest, zinc limitation, hypoxia, and acyl-homoserine lactone quorum sensing. Metabolic pathways for phenazine biosynthesis and denitrification were transcriptionally activated in biofilms. A customized reaction-diffusion model predicted that steep oxygen concentration gradients will form when these biofilms are thicker than about 40 μm. Mutant strains that were deficient in Psl polysaccharide synthesis, the stringent response, the stationary-phase response, and the membrane stress response exhibited increased ciprofloxacin susceptibility when cultured in biofilms. These results support a sequence of phenomena leading to biofilm antibiotic tolerance, involving oxygen limitation, electron acceptor starvation and growth arrest, induction of associated stress responses, and differentiation into protected cell states.IMPORTANCE Bacteria in biofilms are protected from killing by antibiotics, and this reduced susceptibility contributes to the persistence of infections such as those in the cystic fibrosis lung and chronic wounds. A generalized conceptual model of biofilm antimicrobial tolerance with the following mechanistic steps is proposed: (i) establishment of concentration gradients in metabolic substrates and products; (ii) active biological responses to these changes in the local chemical microenvironment; (iii) entry of biofilm cells into a spectrum of states involving alternative metabolisms, stress responses, slow growth, cessation of growth, or dormancy (all prior to antibiotic treatment); (iv) adaptive responses to antibiotic exposure; and (v) reduced susceptibility of microbial cells to antimicrobial challenges in some of the physiological states accessed through these changes.
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Kamischke C, Fan J, Bergeron J, Kulasekara HD, Dalebroux ZD, Burrell A, Kollman JM, Miller SI. The Acinetobacter baumannii Mla system and glycerophospholipid transport to the outer membrane. eLife 2019; 8:e40171. [PMID: 30638443 PMCID: PMC6365058 DOI: 10.7554/elife.40171] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 01/11/2019] [Indexed: 01/14/2023] Open
Abstract
The outer membrane (OM) of Gram-negative bacteria serves as a selective permeability barrier that allows entry of essential nutrients while excluding toxic compounds, including antibiotics. The OM is asymmetric and contains an outer leaflet of lipopolysaccharides (LPS) or lipooligosaccharides (LOS) and an inner leaflet of glycerophospholipids (GPL). We screened Acinetobacter baumannii transposon mutants and identified a number of mutants with OM defects, including an ABC transporter system homologous to the Mla system in E. coli. We further show that this opportunistic, antibiotic-resistant pathogen uses this multicomponent protein complex and ATP hydrolysis at the inner membrane to promote GPL export to the OM. The broad conservation of the Mla system in Gram-negative bacteria suggests the system may play a conserved role in OM biogenesis. The importance of the Mla system to Acinetobacter baumannii OM integrity and antibiotic sensitivity suggests that its components may serve as new antimicrobial therapeutic targets.
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Affiliation(s)
- Cassandra Kamischke
- Department of Microbiology, University of Washington, Seattle, United States
| | - Junping Fan
- Department of Microbiology, University of Washington, Seattle, United States
| | - Julien Bergeron
- Department of Biochemistry, University of Washington, Seattle, United States
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | | | - Zachary D Dalebroux
- Department of Microbiology, University of Washington, Seattle, United States
| | - Anika Burrell
- Department of Biochemistry, University of Washington, Seattle, United States
| | - Justin M Kollman
- Department of Biochemistry, University of Washington, Seattle, United States
| | - Samuel I Miller
- Department of Microbiology, University of Washington, Seattle, United States
- Department of Genome Sciences, University of Washington, Seattle, United States
- Department of Medicine, University of Washington, Seattle, United States
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14
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Yura T, Miyazaki R, Fujiwara K, Ito K, Chiba S, Mori H, Akiyama Y. Heat shock transcription factor σ<sup>32</sup> defective in membrane transport can be suppressed by transposon insertion into genes encoding a restriction enzyme subunit or a putative autotransporter in <i>Escherichia coli</i>. Genes Genet Syst 2018; 93:229-235. [DOI: 10.1266/ggs.18-00040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Affiliation(s)
- Takashi Yura
- Faculty of Life Sciences, Kyoto Sangyo University
| | - Ryoji Miyazaki
- Institute for Frontier Life and Medical Sciences, Kyoto University
| | | | - Koreaki Ito
- Faculty of Life Sciences, Kyoto Sangyo University
| | | | - Hiroyuki Mori
- Institute for Frontier Life and Medical Sciences, Kyoto University
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15
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Molecular Factors of Hypochlorite Tolerance in the Hypersaline Archaeon Haloferax volcanii. Genes (Basel) 2018; 9:genes9110562. [PMID: 30463375 PMCID: PMC6267482 DOI: 10.3390/genes9110562] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 11/07/2018] [Accepted: 11/13/2018] [Indexed: 12/17/2022] Open
Abstract
Halophilic archaea thrive in hypersaline conditions associated with desiccation, ultraviolet (UV) irradiation and redox active compounds, and thus are naturally tolerant to a variety of stresses. Here, we identified mutations that promote enhanced tolerance of halophilic archaea to redox-active compounds using Haloferax volcanii as a model organism. The strains were isolated from a library of random transposon mutants for growth on high doses of sodium hypochlorite (NaOCl), an agent that forms hypochlorous acid (HOCl) and other redox acid compounds common to aqueous environments of high concentrations of chloride. The transposon insertion site in each of twenty isolated clones was mapped using the following: (i) inverse nested two-step PCR (INT-PCR) and (ii) semi-random two-step PCR (ST-PCR). Genes that were found to be disrupted in hypertolerant strains were associated with lysine deacetylation, proteasomes, transporters, polyamine biosynthesis, electron transfer, and other cellular processes. Further analysis revealed a ΔpsmA1 (α1) markerless deletion strain that produces only the α2 and β proteins of 20S proteasomes was hypertolerant to hypochlorite stress compared with wild type, which produces α1, α2, and β proteins. The results of this study provide new insights into archaeal tolerance of redox active compounds such as hypochlorite.
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Lai LY, Lin TL, Chen YY, Hsieh PF, Wang JT. Role of the Mycobacterium marinum ESX-1 Secretion System in Sliding Motility and Biofilm Formation. Front Microbiol 2018; 9:1160. [PMID: 29899738 PMCID: PMC5988883 DOI: 10.3389/fmicb.2018.01160] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 05/14/2018] [Indexed: 11/13/2022] Open
Abstract
Mycobacterium marinum is a close relative of Mycobacterium tuberculosis that can cause systemic tuberculosis-like infections in ectotherms and skin infections in humans. Sliding motility correlates with biofilm formation and virulence in most bacteria. In this study, we used a sliding motility assay to screen 2,304 transposon mutants of M. marinum NTUH-M6885 and identified five transposon mutants with decreased sliding motility. Transposons that interrupted the type VII secretion system (T7SS) ESX-1-related genes, espE (mmar_5439), espF (mmar_5440), and eccA1 (mmar_5443), were present in 3 mutants. We performed reverse-transcription polymerase chain reaction to verify genes from mmar_5438 to mmar_5450, which were found to belong to a single transcriptional unit. Deletion mutants of espE, espF, espG (mmar_5441), and espH (mmar_5442) displayed significant attenuation regarding sliding motility and biofilm formation. M. marinum NTUH-M6885 possesses a functional ESX-1 secretion system. However, deletion of espG or espH resulted in slightly decreased secretion of EsxB (which is also known as CFP-10). Thus, the M. marinum ESX-1 secretion system mediates sliding motility and is crucial for biofilm formation. These data provide new insight into M. marinum biofilm formation.
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Affiliation(s)
- Li-Yin Lai
- Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Tzu-Lung Lin
- Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Yi-Yin Chen
- Department of Pediatrics, Chang Gung Children's Hospital, Chang Gung Memorial Hospital, College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Pei-Fang Hsieh
- Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Jin-Town Wang
- Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan.,Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
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17
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Damavandi N, Raigani M, Joudaki A, Davami F, Zeinali S. Rapid characterization of the CHO platform cell line and identification of pseudo attP sites for PhiC31 integrase. Protein Expr Purif 2017; 140:60-64. [DOI: 10.1016/j.pep.2017.08.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2017] [Revised: 08/02/2017] [Accepted: 08/08/2017] [Indexed: 11/26/2022]
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18
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Anzai IA, Shaket L, Adesina O, Baym M, Barstow B. Rapid curation of gene disruption collections using Knockout Sudoku. Nat Protoc 2017; 12:2110-2137. [DOI: 10.1038/nprot.2017.073] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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19
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Rapid construction of a whole-genome transposon insertion collection for Shewanella oneidensis by Knockout Sudoku. Nat Commun 2016; 7:13270. [PMID: 27830751 PMCID: PMC5109470 DOI: 10.1038/ncomms13270] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 09/14/2016] [Indexed: 02/07/2023] Open
Abstract
Whole-genome knockout collections are invaluable for connecting gene sequence to function, yet traditionally, their construction has required an extraordinary technical effort. Here we report a method for the construction and purification of a curated whole-genome collection of single-gene transposon disruption mutants termed Knockout Sudoku. Using simple combinatorial pooling, a highly oversampled collection of mutants is condensed into a next-generation sequencing library in a single day, a 30- to 100-fold improvement over prior methods. The identities of the mutants in the collection are then solved by a probabilistic algorithm that uses internal self-consistency within the sequencing data set, followed by rapid algorithmically guided condensation to a minimal representative set of mutants, validation, and curation. Starting from a progenitor collection of 39,918 mutants, we compile a quality-controlled knockout collection of the electroactive microbe Shewanella oneidensis MR-1 containing representatives for 3,667 genes that is functionally validated by high-throughput kinetic measurements of quinone reduction. Knockout collections provide a valuable tool to explore gene function, yet are expensive and technically challenging to produce at a genome-wide scale. Here Baym et al. devise a cost-effective transposon-based method to quickly develop a knockout collection for the electroactive microbe Shewanella oneidensis.
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20
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Chen YY, Yang FL, Wu SH, Lin TL, Wang JT. Mycobacterium marinum mmar_2318 and mmar_2319 are Responsible for Lipooligosaccharide Biosynthesis and Virulence Toward Dictyostelium. Front Microbiol 2016; 6:1458. [PMID: 26779131 PMCID: PMC4703794 DOI: 10.3389/fmicb.2015.01458] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Accepted: 12/04/2015] [Indexed: 12/15/2022] Open
Abstract
Resistance to phagocyte killing is an important virulence factor in mycobacteria. Dictyostelium has been used to study the interaction between phagocytes and bacteria, given its similarity to the mammalian macrophage. Here, we investigated the genes responsible for virulence to Dictyostelium by screening 1728 transposon mutants of the Mycobacterium marinum NTUH-M6094 strain. A total of 30 mutants that permissive for Dictyostelium growth were identified. These mutants revealed interruptions in 20 distinct loci. Of the 20 loci, six genes (losA, mmar_2318, mmar_2319, wecE, mmar_2323 and mmar_2353) were located in the lipooligosaccharide (LOS) synthesis cluster. LOS are antigenic glycolipids and the core LOS structure from LOS-I to LOS-IV have been reported to exist in M. marinum. Two-dimensional thin-layer chromatography (2D-TLC) glycolipid profiles revealed that deletion of mmar_2318 or mmar_2319 resulted in the accumulation of LOS-III and deficiency of LOS-IV. Deletion and complementation of mmar_2318 or mmar_2319 confirmed that these genes both contributed to virulence toward Dictyostelium but not entry and replication inside Dictyostelium. Co-incubation with a murine macrophage cell line J774a.1 or PMA-induced human monocytic cell line THP-1 demonstrated that mmar_2318 or mmar_2319 deletion mutant could grow in macrophages, and their initial entry rate was not affected in J774a.1 but significantly increased in THP-1. In conclusion, although mmar_2319 has been reported to involve LOS biosynthesis in a previous study, we identified a new gene, mmar_2318 that is also involved in the biosynthesis of LOS. Deletion of mmar_2318 or mmar_2319 both exhibits reduction of virulence toward Dictyostelium and increased entry into THP-1 cells.
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Affiliation(s)
- Yi-Yin Chen
- Department of Microbiology, National Taiwan University College of Medicine Taipei, Taiwan
| | - Feng-Ling Yang
- Institute of Biological Chemistry, Academia Sinica Taipei, Taiwan
| | - Shih-Hsiung Wu
- Institute of Biological Chemistry, Academia Sinica Taipei, Taiwan
| | - Tzu-Lung Lin
- Department of Microbiology, National Taiwan University College of Medicine Taipei, Taiwan
| | - Jin-Town Wang
- Department of Microbiology, National Taiwan University College of MedicineTaipei, Taiwan; Department of Internal Medicine, National Taiwan University HospitalTaipei, Taiwan
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21
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Sarcosine Catabolism in Pseudomonas aeruginosa Is Transcriptionally Regulated by SouR. J Bacteriol 2015; 198:301-10. [PMID: 26503852 DOI: 10.1128/jb.00739-15] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 10/22/2015] [Indexed: 01/18/2023] Open
Abstract
UNLABELLED Sarcosine (N-methylglycine) is present in many environments inhabited by pseudomonads and is likely most often encountered as an intermediate in the metabolism of choline, carnitine, creatine, and glyphosate. While the enzymology of sarcosine metabolism has been relatively well studied in bacteria, the regulatory mechanisms governing catabolism have remained largely unknown. We previously determined that the sarcosine-catabolic (sox) operon of Pseudomonas aeruginosa is induced by the AraC family regulator GbdR in response to glycine betaine and dimethylglycine. However, induction of these genes was still observed in response to sarcosine in a gbdR deletion mutant, indicating that an independent sarcosine-responsive transcription factor also acted at this locus. Our goal in this study was to identify and characterize this regulator. Using a transposon-based genetic screen, we identified PA4184, or SouR (sarcosine oxidation and utilization regulator), as the sarcosine-responsive regulator of the sox operon, with tight induction specificity for sarcosine. The souR gene is required for appreciable growth on sarcosine as a carbon and nitrogen source. We also characterized the transcriptome response to sarcosine governed by SouR using microarray analyses and performed electrophoretic mobility shift assays to identify promoters directly regulated by the transcription factor. Finally, we characterized PA3630, or GfnR (glutathione-dependent formaldehyde neutralization regulator), as the regulator of the glutathione-dependent formaldehyde detoxification system in P. aeruginosa that is expressed in response to formaldehyde released during the catabolism of sarcosine. This study expands our understanding of sarcosine metabolic regulation in bacteria through the identification and characterization of the first known sarcosine-responsive transcriptional regulator. IMPORTANCE The Pseudomonas aeruginosa genome encodes many diverse metabolic pathways, yet the specific transcription regulators controlling their expression remain mostly unknown. Here, we used a genetic screen to identify the sarcosine-specific regulator of the sarcosine oxidase operon, which we have named SouR. SouR is the first bacterial regulator shown to respond to sarcosine, and it is required for growth on sarcosine. Sarcosine is found in its free form and is also an intermediate in the catabolic pathways of glycine betaine, carnitine, creatine, and glyphosate. The similarity of SouR to the regulators of carnitine and glycine betaine catabolism suggests evolutionary diversification within this regulatory family to allow response to structurally similar but physiologically distinct ligands.
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22
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Ellis MJ, Trussler RS, Haniford DB. A cis-encoded sRNA, Hfq and mRNA secondary structure act independently to suppress IS200 transposition. Nucleic Acids Res 2015; 43:6511-27. [PMID: 26044710 PMCID: PMC4513863 DOI: 10.1093/nar/gkv584] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 05/22/2015] [Indexed: 12/13/2022] Open
Abstract
IS200 is found throughout Enterobacteriaceae and transposes at a notoriously low frequency. In addition to the transposase protein (TnpA), IS200 encodes an uncharacterized Hfq-binding sRNA that is encoded opposite to the tnpA 5'UTR. In the current work we asked if this sRNA represses tnpA expression. We show here that the IS200 sRNA (named art200 for antisense regulator of transposase IS200) basepairs with tnpA to inhibit translation initiation. Unexpectedly, art200-tnpA pairing is limited to 40 bp, despite 90 nt of perfect complementarity. Additionally, we show that Hfq and RNA secondary structure in the tnpA 5'UTR each repress tnpA expression in an art200-independent manner. Finally, we show that disrupting translational control of tnpA expression leads to increased IS200 transposition in E. coli. The current work provides new mechanistic insight into why IS200 transposition is so strongly suppressed. The possibility of art200 acting in trans to regulate a yet-unidentified target is discussed as well as potential applications of the IS200 system for designing novel riboregulators.
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Affiliation(s)
- Michael J Ellis
- Department of Biochemistry, University of Western Ontario, London, ON, N6A 5C1, Canada
| | - Ryan S Trussler
- Department of Biochemistry, University of Western Ontario, London, ON, N6A 5C1, Canada
| | - David B Haniford
- Department of Biochemistry, University of Western Ontario, London, ON, N6A 5C1, Canada
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23
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Evangelinos M, Anagnostopoulos G, Karvela-Kalogeraki I, Stathopoulou PM, Scazzocchio C, Diallinas G. Minos as a novel Tc1/mariner-type transposable element for functional genomic analysis in Aspergillus nidulans. Fungal Genet Biol 2015; 81:1-11. [PMID: 26021704 DOI: 10.1016/j.fgb.2015.05.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Revised: 05/15/2015] [Accepted: 05/18/2015] [Indexed: 10/23/2022]
Abstract
Transposons constitute powerful genetic tools for gene inactivation, exon or promoter trapping and genome analyses. The Minos element from Drosophila hydei, a Tc1/mariner-like transposon, has proved as a very efficient tool for heterologous transposition in several metazoa. In filamentous fungi, only a handful of fungal-specific transposable elements have been exploited as genetic tools, with the impala Tc1/mariner element from Fusarium oxysporum being the most successful. Here, we developed a two-component transposition system to manipulate Minos transposition in Aspergillus nidulans (AnMinos). Our system allows direct selection of transposition events based on re-activation of niaD, a gene necessary for growth on nitrate as a nitrogen source. On average, among 10(8) conidiospores, we obtain up to ∼0.8×10(2) transposition events leading to the expected revertant phenotype (niaD(+)), while ∼16% of excision events lead to AnMinos loss. Characterized excision footprints consisted of the four terminal bases of the transposon flanked by the TA target duplication and led to no major DNA rearrangements. AnMinos transposition depends on the presence of its homologous transposase. Its frequency was not significantly affected by temperature, UV irradiation or the transcription status of the original integration locus (niaD). Importantly, transposition is dependent on nkuA, encoding an enzyme essential for non-homologous end joining of DNA in double-strand break repair. AnMinos proved to be an efficient tool for functional analysis as it seems to transpose in different genomic loci positions in all chromosomes, including a high proportion of integration events within or close to genes. We have used Minos to obtain morphological and toxic analogue resistant mutants. Interestingly, among morphological mutants some seem to be due to Minos-elicited over-expression of specific genes, rather than gene inactivation.
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Affiliation(s)
- Minoas Evangelinos
- Faculty of Biology, University of Athens, Panepistimioupolis, Athens 15784, Greece
| | | | | | | | - Claudio Scazzocchio
- Department of Microbiology, Imperial College London, London SW7 2AZ, United Kingdom; Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Bâtiment 400, 91405 Orsay Cedex, France
| | - George Diallinas
- Faculty of Biology, University of Athens, Panepistimioupolis, Athens 15784, Greece.
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24
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Hsieh PF, Wu MC, Yang FL, Chen CT, Lou TC, Chen YY, Wu SH, Sheu JC, Wang JT. D-galactan II is an immunodominant antigen in O1 lipopolysaccharide and affects virulence in Klebsiella pneumoniae: implication in vaccine design. Front Microbiol 2014; 5:608. [PMID: 25477867 PMCID: PMC4237132 DOI: 10.3389/fmicb.2014.00608] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 10/24/2014] [Indexed: 01/07/2023] Open
Abstract
In the O1 strain of Klebsiella, the lipopolysaccharide (LPS) O-antigen is composed of D-galactan I and D-galactan II. Although the composition of the O1 antigen of Klebsiella was resolved more than two decades, the genetic locus involved in the biosynthesis of D-galactan II and the role of D-galactan II in bacterial pathogenesis remain unclear. Here, we report the identification of the D-galactan II-synthesizing genes by screening a transposon mutant library of an acapsulated Klebsiella pneumoniae O1 strain with bacteriophage. K. pneumoniae strain deleted for wbbY exhibited abrogated D-galactan II production; altered serum resistance and attenuation of virulence. Serologic analysis of K. pneumoniae clinical isolates demonstrated that D-galactan II was more prevalent in community-acquired pyogenic liver abscess (PLA)—causing strains than in non-tissue-invasive strains. WbbY homologs, WbbZ homologs, and lipopolysaccharide structures based on D-galactan II also were present in several Gram-negative bacteria. Immunization of mice with the magA-mutant (K−1 O1) (that is, with a LPS D-galactan II-producing strain) provided protection against infection with an O1:K2 PLA strain. Our findings indicate that both WbbY and WbbZ homologs are sufficient for the synthesis of D-galactan II. D-galactan II represents an immunodominant antigen; is conserved among multiple species of Gram-negative bacteria and could be a useful vaccine candidate.
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Affiliation(s)
- Pei-Fang Hsieh
- Department of Microbiology, National Taiwan University College of Medicine Taipei, Taiwan
| | - Meng-Chuan Wu
- Department of Internal Medicine, National Taiwan University Hospital Taipei, Taiwan
| | - Feng-Ling Yang
- The Institute of Biological Chemistry, Academia Sinica Taipei, Taiwan
| | - Chun-Tang Chen
- Department of Microbiology, National Taiwan University College of Medicine Taipei, Taiwan
| | - Tzu-Chi Lou
- The Institute of Biological Chemistry, Academia Sinica Taipei, Taiwan
| | - Yi-Yin Chen
- Department of Microbiology, National Taiwan University College of Medicine Taipei, Taiwan
| | - Shih-Hsiung Wu
- The Institute of Biological Chemistry, Academia Sinica Taipei, Taiwan
| | - Jin-Chuan Sheu
- Department of Internal Medicine, National Taiwan University Hospital Taipei, Taiwan
| | - Jin-Town Wang
- Department of Microbiology, National Taiwan University College of Medicine Taipei, Taiwan ; Department of Internal Medicine, National Taiwan University Hospital Taipei, Taiwan
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25
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Patterns of expression and translocation of the ubiquitin ligase SlrP in Salmonella enterica serovar Typhimurium. J Bacteriol 2014; 196:3912-22. [PMID: 25182488 DOI: 10.1128/jb.02158-14] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
SlrP is an E3 ubiquitin ligase that can be translocated into eukaryotic host cells by the two type III secretion systems that are expressed by Salmonella enterica serovar Typhimurium and are encoded in Salmonella pathogenicity islands 1 (SPI1) and 2 (SPI2). Expression of slrP and translocation of its product were examined using lac, 3×FLAG, and cyaA' translational fusions. Although slrP was expressed in different media, optimal expression was found under conditions that imitate the intravacuolar environment and promote synthesis of the SPI2-encoded type III secretion system. Translocation into mammalian cells took place through the SPI1- or the SPI2-encoded type III secretion system, depending on specific host cell type and timing. A search for genetic factors involved in controlling the expression of slrP unveiled LeuO, Lon, and the two-component system PhoQ/PhoP as novel regulators of slrP. Our experiments suggest that LeuO and Lon act through HilD under SPI1-inducing conditions, whereas PhoP directly interacts with the slrP promoter to activate transcription under SPI2 inducing conditions.
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26
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Watson E, MacNeil LT, Ritter AD, Yilmaz LS, Rosebrock AP, Caudy AA, Walhout AJM. Interspecies systems biology uncovers metabolites affecting C. elegans gene expression and life history traits. Cell 2014; 156:759-70. [PMID: 24529378 PMCID: PMC4169190 DOI: 10.1016/j.cell.2014.01.047] [Citation(s) in RCA: 131] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Revised: 10/09/2013] [Accepted: 01/09/2014] [Indexed: 01/07/2023]
Abstract
Diet greatly influences gene expression and physiology. In mammals, elucidating the effects and mechanisms of individual nutrients is challenging due to the complexity of both the animal and its diet. Here, we used an interspecies systems biology approach with Caenorhabditis elegans and two of its bacterial diets, Escherichia coli and Comamonas aquatica, to identify metabolites that affect the animal's gene expression and physiology. We identify vitamin B12 as the major dilutable metabolite provided by Comamonas aq. that regulates gene expression, accelerates development, and reduces fertility but does not affect lifespan. We find that vitamin B12 has a dual role in the animal: it affects development and fertility via the methionine/S-Adenosylmethionine (SAM) cycle and breaks down the short-chain fatty acid propionic acid, preventing its toxic buildup. Our interspecies systems biology approach provides a paradigm for understanding complex interactions between diet and physiology.
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Affiliation(s)
- Emma Watson
- Program in Systems Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA; Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Lesley T MacNeil
- Program in Systems Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA; Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Ashlyn D Ritter
- Program in Systems Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA; Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - L Safak Yilmaz
- Program in Systems Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA; Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Adam P Rosebrock
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto M5S 3E1, Canada; Department of Molecular Genetics, University of Toronto, Toronto M5S 3E1, Canada
| | - Amy A Caudy
- Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto M5S 3E1, Canada; Department of Molecular Genetics, University of Toronto, Toronto M5S 3E1, Canada
| | - Albertha J M Walhout
- Program in Systems Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA; Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA.
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27
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Espinosa E, Casadesús J. Regulation of Salmonella enterica pathogenicity island 1 (SPI-1) by the LysR-type regulator LeuO. Mol Microbiol 2014; 91:1057-69. [PMID: 24354910 DOI: 10.1111/mmi.12500] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/18/2013] [Indexed: 12/11/2022]
Abstract
LeuO is a quiescent LysR-type regulator belonging to the H-NS regulon. Activation of leuO transcription represses expression of pathogenicity island 1 (SPI-1) in Salmonella enterica serovar Typhimurium and inhibits invasion of epithelial cells. Loss of HilE suppresses LeuO-mediated downregulation of SPI-1. Activation of leuO transcription reduces the level of HilD protein, and loss of HilE restores the wild type HilD level. Hence, LeuO-mediated downregulation of SPI-1 may involve inhibition of HilD activity by HilE, a view consistent with the fact that HilE is a HilD inhibitor. In vivo analyses using β-galactosidase fusions indicate that LeuO activates hilE transcription. In vitro analyses by slot blotting, electrophoretic mobility shift analysis and DNase I footprinting show that LeuO binds the hilE promoter region. Although residual SPI-1 repression by LeuO is observed in the absence of HilE, the LeuO-HilE-HilD 'pathway' appears to be the major mechanism. Because both leuO and SPI-1 are repressed by H-NS, activation of leuO transcription may provide a backup mechanism for SPI-1 repression under conditions that impair H-NS-mediated silencing.
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Affiliation(s)
- Elena Espinosa
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, Sevilla, E-41080, Spain
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Abstract
Transposon-based mutagenesis of bacterial genomes is a powerful method to identify genetic elements that control specific phenotypes. The most frequently used transposon tools in Pseudomonas aeruginosa are based either on Himar1 mariner or Tn5 transposases, both of which have been used to generate nonredundant mutant libraries in P. aeruginosa. Here we present a detailed protocol for using Himar1 mariner-based transposon mutagenesis to create mutant libraries in P. aeruginosa.
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Affiliation(s)
- Hemantha D Kulasekara
- Department of Microbiology, University of Washington, 1959 NE Pacific St HSB K161, Seattle, WA, 98195, USA,
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DsbA and MgrB regulate steA expression through the two-component system PhoQ/PhoP in Salmonella enterica. J Bacteriol 2013; 195:2368-78. [PMID: 23504014 DOI: 10.1128/jb.00110-13] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
SteA is a protein that can be translocated into host cells through the two virulence-related type III secretion systems that are present in Salmonella enterica. We used the T-POP system to carry out general screens for loci that exhibited activation or repression of a steA::lacZ fusion. These screens identified the histidine kinase PhoQ and the response regulator PhoP as positive regulators of steA. Transcription of this gene is σ70 dependent, and the promoter of steA contains a PhoP-binding site that mediates direct regulation by PhoP. Our screens also detected MgrB (also known as YobG) as a negative regulator of the expression of steA. Disruption of the gene encoding the periplasmic disulfide oxidoreductase DsbA or addition of the reducing agent dithiothreitol increases transcription of steA. The effects of MgrB and DsbA on steA are mediated by PhoP. These results suggest that the cellular redox status is a factor contributing to regulation of steA and, probably, other virulence genes regulated by the PhoQ/PhoP two-component system.
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Cheng C, Nair ADS, Indukuri VV, Gong S, Felsheim RF, Jaworski D, Munderloh UG, Ganta RR. Targeted and random mutagenesis of Ehrlichia chaffeensis for the identification of genes required for in vivo infection. PLoS Pathog 2013; 9:e1003171. [PMID: 23459099 PMCID: PMC3573109 DOI: 10.1371/journal.ppat.1003171] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2012] [Accepted: 12/10/2012] [Indexed: 11/19/2022] Open
Abstract
Ehrlichia chaffeensis is a tick transmitted pathogen responsible for the disease human monocytic ehrlichiosis. Research to elucidate gene function in rickettsial pathogens is limited by the lack of genetic manipulation methods. Mutational analysis was performed, targeting to specific and random insertion sites within the bacterium's genome. Targeted mutagenesis at six genomic locations by homologous recombination and mobile group II intron-based methods led to the consistent identification of mutants in two genes and in one intergenic site; the mutants persisted in culture for 8 days. Three independent experiments using Himar1 transposon mutagenesis of E. chaffeensis resulted in the identification of multiple mutants; these mutants grew continuously in macrophage and tick cell lines. Nine mutations were confirmed by sequence analysis. Six insertions were located within non-coding regions and three were present in the coding regions of three transcriptionally active genes. The intragenic mutations prevented transcription of all three genes. Transposon mutants containing a pool of five different insertions were assessed for their ability to infect deer and subsequent acquisition by Amblyomma americanum ticks, the natural reservoir and vector, respectively. Three of the five mutants with insertions into non-coding regions grew well in deer. Transposition into a differentially expressed hypothetical gene, Ech_0379, and at 18 nucleotides downstream to Ech_0230 gene coding sequence resulted in the inhibition of growth in deer, which is further evidenced by their failed acquisition by ticks. Similarly, a mutation into the coding region of ECH_0660 gene inhibited the in vivo growth in deer. This is the first study evaluating targeted and random mutagenesis in E. chaffeensis, and the first to report the generation of stable mutants in this obligate intracellular bacterium. We further demonstrate that in vitro mutagenesis coupled with in vivo infection assessment is a successful strategy in identifying genomic regions required for the pathogen's in vivo growth. The tick-transmitted bacterium, Ehrlichia chaffeensis, causes human monocytic ehrlichiosis, an acute febrile illness that can progress to a fatal outcome. This and other related pathogens have evolved to establish infections in vertebrate and tick hosts for completing their lifecycle. Our recent studies suggest that the pathogen's differential gene expression during growth in ticks and mammals is a major contributor for its dual host adaptation. However, the importance of the pathogen phenotype differences is best understood if we have methods to knock down protein expression from one or more genes. Creating mutations in obligate intracellular pathogens remain a challenge due to their limited survival in the extracellular environment. Here, we present evidence for multiple insertion mutations in the E. chaffeensis genome. Three of the nine mutations in the genome inhibiting gene expression prevented infection of deer, the natural host for the pathogen. This is the first study demonstrating the feasibility of creating mutations in an Ehrlichia species; and directly linking specific regions of the genome to in vivo infection. Methods described here allow for studies to define genes important for infectivity and ability to cause disease, and are equally important for initiating similar studies in other related emerging zoonotic pathogens.
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Affiliation(s)
- Chuanmin Cheng
- Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America
| | - Arathy D. S. Nair
- Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America
| | - Vijaya V. Indukuri
- Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America
| | - Shanzhong Gong
- Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America
| | - Roderick F. Felsheim
- Department of Entomology, University of Minnesota, St. Paul, Minnesota, United States of America
| | - Deborah Jaworski
- Department of Entomology and Plant Pathology, Oklahoma State University, Noble Research Center, Stillwater, Oklahoma, United States of America
| | - Ulrike G. Munderloh
- Department of Entomology, University of Minnesota, St. Paul, Minnesota, United States of America
| | - Roman R. Ganta
- Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas, United States of America
- * E-mail:
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Baisón-Olmo F, Cardenal-Muñoz E, Ramos-Morales F. PipB2 is a substrate of the Salmonella pathogenicity island 1-encoded type III secretion system. Biochem Biophys Res Commun 2012; 423:240-6. [DOI: 10.1016/j.bbrc.2012.05.095] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Accepted: 05/17/2012] [Indexed: 12/14/2022]
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SrfJ, a Salmonella type III secretion system effector regulated by PhoP, RcsB, and IolR. J Bacteriol 2012; 194:4226-36. [PMID: 22661691 DOI: 10.1128/jb.00173-12] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Virulence-related type III secretion systems are present in many Gram-negative bacterial pathogens. These complex devices translocate proteins, called effectors, from the bacterium into the eukaryotic host cell. Here, we identify the product of srfJ, a Salmonella enterica serovar Typhimurium gene regulated by SsrB, as a new substrate of the type III secretion system encoded by Salmonella pathogenicity island 2. The N-terminal 20-amino-acid segment of SrfJ was recognized as a functional secretion and translocation signal specific for this system. Transcription of srfJ was positively regulated by the PhoP/PhoQ system in an SsrB-dependent manner and was negatively regulated by the Rcs system in an SsrB-independent manner. A screen for regulators of an srfJ-lacZ transcriptional fusion using the T-POP transposon identified IolR, the regulator of genes involved in myo-inositol utilization, as an srfJ repressor. Our results suggest that SrfJ is synthesized both inside the host, in response to intracellular conditions, and outside the host, in myo-inositol-rich environments.
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Abstract
Central to Q fever pathogenesis is replication of the causative agent, Coxiella burnetii, within a phagolysosome-like parasitophorous vacuole (PV) in mononuclear phagocytes. C. burnetii modulates PV biogenesis and other host cell functions, such as apoptotic signaling, presumably via the activity of proteins delivered to the host cytosol by a Dot/Icm type IVB secretion system (T4BSS). In this study, we utilized a C. burnetii strain carrying IcmD inactivated by the Himar1 transposon to investigate the requirements for Dot/Icm function in C. burnetii parasitism of human THP-1 macrophage-like cells. The icmD::Tn mutant failed to secrete characterized T4BSS substrates, a defect that correlated with deficient replication, PV development, and apoptosis protection. Restoration of type IVB secretion and intracellular growth of the icmD::Tn mutant required complementation with icmD, -J, and -B, indicating a polar effect of the transposon insertion on downstream dot/icm genes. Induction of icmDJB expression at 1 day postinfection resulted in C. burnetii replication and PV generation. Collectively, these data prove that T4BSS function is required for productive infection of human macrophages by C. burnetii. However, illustrating the metabolic flexibility of C. burnetti, the icmD::Tn mutant could replicate intracellularly when sequestered in a PV generated by wild-type bacteria, where Dot/Icm function is provided in trans, and within a phenotypically similar PV generated by the protozoan parasite Leishmania amazonensis, where host cells are devoid of Dot/Icm T4BSS effector proteins. Coxiella burnetii, the cause of human Q fever, is the only bacterial pathogen known to replicate in a vacuole resembling a phagolysosome. The organism manipulates host macrophages to promote the biogenesis of a vacuolar compartment permissive for growth. By analogy to the well-established cellular microbiology of Legionella pneumophila, the Dot/Icm type IVB secretion system of C. burnetii is implicated as a critical virulence factor in host cell modification that delivers proteins with effector functions directly into the host cell cytosol. Using new genetic tools, we verify that Dot/Icm function is essential for productive infection of human macrophages by C. burnetii. Interestingly, despite the production of homologous secretion systems, L. pneumophila and C. burnetii have strikingly different temporal requirements for Dot/Icm function during their respective infectious cycles.
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Use of a Dictyostelium model for isolation of genetic loci associated with phagocytosis and virulence in Klebsiella pneumoniae. Infect Immun 2010; 79:997-1006. [PMID: 21173313 DOI: 10.1128/iai.00906-10] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Phagocytosis resistance is an important virulence factor in Klebsiella pneumoniae. Dictyostelium has been used to study the interaction between phagocytes and bacteria because of its similarity to mammalian macrophages. In this study, we used a Dictyostelium model to investigate genes for resistance to phagocytosis in NTUH-K2044, a strain of K. pneumoniae causing pyogenic liver abscess that is highly resistant to phagocytosis. A total of 2,500 transposon mutants were screened by plaque assay, and 29 of them permitted phagocytosis by Dictyostelium. In the 29 mutants, six loci were identified; three were capsular synthesis genes. Of the other three, one was related to carnitine metabolism, one encoded a subunit of protease (clpX), and one encoded a lipopolysaccharide O-antigen transporter (wzm). Deletion and complementation of these genes showed that only ΔclpX and Δwzm mutants became susceptible to Dictyostelium phagocytosis, and their complementation restored the phagocytosis resistance phenotype. These two mutants were also susceptible to phagocytosis by human neutrophils and revealed attenuated virulence in a mouse model, implying that they play important roles in the pathogenesis of K. pneumoniae. Furthermore, we demonstrated that clpP, which exists in an operon with clpX, was also involved in resistance to phagocytosis. The transcriptional profile of ΔclpX was examined by microarray analysis and revealed a 3-fold lower level of expression of capsular synthesis genes. Therefore, we have identified genes involved in resistance to phagocytosis in K. pneumoniae using Dictyostelium, and this model is useful to explore genes associated with resistance to phagocytosis in heavily encapsulated bacteria.
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BglJ-RcsB heterodimers relieve repression of the Escherichia coli bgl operon by H-NS. J Bacteriol 2010; 192:6456-64. [PMID: 20952573 DOI: 10.1128/jb.00807-10] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
RcsB is the response regulator of the complex Rcs two-component system, which senses perturbations in the outer membrane and peptidoglycan layer. BglJ is a transcriptional regulator whose constitutive expression causes activation of the H-NS- and StpA-repressed bgl (aryl-β,D-glucoside) operon in Escherichia coli. RcsB and BglJ both belong to the LuxR-type family of transcriptional regulators with a characteristic C-terminal DNA-binding domain. Here, we show that BglJ and RcsB interact and form heterodimers that presumably bind upstream of the bgl promoter, as suggested by mutation of a sequence motif related to the consensus sequence for RcsA-RcsB heterodimers. Heterodimerization of BglJ-RcsB and relief of H-NS-mediated repression of bgl by BglJ-RcsB are apparently independent of RcsB phosphorylation. In addition, we show that LeuO, a pleiotropic LysR-type transcriptional regulator, likewise binds to the bgl upstream regulatory region and relieves repression of bgl independently of BglJ-RcsB. Thus, LeuO can affect bgl directly, as shown here, and indirectly by activating the H-NS-repressed yjjQ-bglJ operon, as shown previously. Taken together, heterodimer formation of RcsB and BglJ expands the role of the Rcs two-component system and the network of regulators affecting the bgl promoter.
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Hölscher T, Breuer U, Adrian L, Harms H, Maskow T. Production of the chiral compound (R)-3-hydroxybutyrate by a genetically engineered methylotrophic bacterium. Appl Environ Microbiol 2010; 76:5585-91. [PMID: 20581197 PMCID: PMC2918973 DOI: 10.1128/aem.01065-10] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Accepted: 06/11/2010] [Indexed: 11/20/2022] Open
Abstract
In this study, a methylotrophic bacterium, Methylobacterium rhodesianum MB 126, was used for the production of the chiral compound (R)-3-hydroxybutyrate (R-3HB) from methanol. R-3HB is formed during intracellular degradation of the storage polymer (R)-3-polyhydroxybutyrate (PHB). Since the monomer R-3HB does not accumulate under natural conditions, M. rhodesianum was genetically modified. The gene (hbd) encoding the R-3HB-degrading enzyme, R-3HB dehydrogenase, was inactivated in M. rhodesianum. The resulting hbd mutant still exhibited low growth rates on R-3HB as the sole source of carbon and energy, indicating the presence of alternative pathways for R-3HB utilization. Therefore, transposon mutagenesis was carried out with the hbd mutant, and a double mutant unable to grow on R-3HB was obtained. This mutant was shown to be defective in lipoic acid synthase (LipA), resulting in an incomplete citric acid cycle. Using the hbd lipA mutant, we produced 3.2 to 3.5 mM R-3HB in batch and 27 mM (2,800 mg liter(-1)) in fed-batch cultures. This was achieved by sequences of cultivation conditions initially favoring growth, then PHB accumulation, and finally PHB degradation.
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Affiliation(s)
- Tina Hölscher
- UFZ-Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany
| | - Uta Breuer
- UFZ-Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany
| | - Lorenz Adrian
- UFZ-Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany
| | - Hauke Harms
- UFZ-Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany
| | - Thomas Maskow
- UFZ-Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany
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37
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Structural characterization of ISCR8, ISCR22, and ISCR23, subgroups of IS91-like insertion elements. Antimicrob Agents Chemother 2010; 54:4321-8. [PMID: 20625149 DOI: 10.1128/aac.00006-10] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Analysis of ISCR8 (ISPps1) revealed that this group of insertion elements has to be subdivided into three subgroups: ISCR8, ISCR22, and ISCR23. The distinction of three subgroups is supported by phylogenetic analysis of the transposase open reading frames (ORFs). Comparison of over 20 complete and partial ISCR8/22/23 elements identified oriIS candidate sequences for all groups and a terIS candidate sequence for ISCR8. The oriIS sequences, their distance to the transposase ORFs, and the sequence of this intervening region are group specific, further supporting the definition of two new ISCR elements. ISCR8/22/23 have a very broad host range, including Gram-positive and Gram-negative bacteria, among which are several (opportunistic) pathogens. The IS often resides on plasmids or in the vicinity of other mobile elements and is mostly associated with genes for the degradation of halo- or nitro-aromatics. However, in one case ISCR8 was found in the neighborhood of an antibiotic resistance determinant in Klebsiella pneumoniae. ISCR8 resembles other IS91 family elements in mediating genetic rearrangements by homologous recombination between two copies. In Delftia acidovorans this led to the loss of the genes encoding dichlorprop cleavage. In conclusion, this study shows that ISCR8 could be a fully functional and active member of the IS91 family of insertion elements.
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Granek JA, Magwene PM. Environmental and genetic determinants of colony morphology in yeast. PLoS Genet 2010; 6:e1000823. [PMID: 20107600 PMCID: PMC2809765 DOI: 10.1371/journal.pgen.1000823] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Accepted: 12/21/2009] [Indexed: 12/30/2022] Open
Abstract
Nutrient stresses trigger a variety of developmental switches in the budding yeast Saccharomyces cerevisiae. One of the least understood of such responses is the development of complex colony morphology, characterized by intricate, organized, and strain-specific patterns of colony growth and architecture. The genetic bases of this phenotype and the key environmental signals involved in its induction have heretofore remained poorly understood. By surveying multiple strain backgrounds and a large number of growth conditions, we show that limitation for fermentable carbon sources coupled with a rich nitrogen source is the primary trigger for the colony morphology response in budding yeast. Using knockout mutants and transposon-mediated mutagenesis, we demonstrate that two key signaling networks regulating this response are the filamentous growth MAP kinase cascade and the Ras-cAMP-PKA pathway. We further show synergistic epistasis between Rim15, a kinase involved in integration of nutrient signals, and other genes in these pathways. Ploidy, mating-type, and genotype-by-environment interactions also appear to play a role in the controlling colony morphology. Our study highlights the high degree of network reuse in this model eukaryote; yeast use the same core signaling pathways in multiple contexts to integrate information about environmental and physiological states and generate diverse developmental outputs.
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Affiliation(s)
- Joshua A. Granek
- Department of Biology and Center for Systems Biology, Duke University, Durham, North Carolina, United States of America
| | - Paul M. Magwene
- Department of Biology and Center for Systems Biology, Duke University, Durham, North Carolina, United States of America
- * E-mail:
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The transposon impala is activated by low temperatures: use of a controlled transposition system to identify genes critical for viability of Aspergillus fumigatus. EUKARYOTIC CELL 2010; 9:438-48. [PMID: 20097738 DOI: 10.1128/ec.00324-09] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Genes that are essential for viability represent potential targets for the development of anti-infective agents. However, relatively few have been determined in the filamentous fungal pathogen Aspergillus fumigatus. A novel solution employing parasexual genetics coupled with transposon mutagenesis using the Fusarium oxysporum transposon impala had previously enabled the identification of 20 essential genes from A. fumigatus; however, further use of this system required a better understanding of the mode of action of the transposon itself. Examination of a range of conditions indicated that impala is activated by prolonged exposure to low temperatures. This newly identified property was then harnessed to identify 96 loci that are critical for viability in A. fumigatus, including genes required for RNA metabolism, organelle organization, protein transport, ribosome biogenesis, and transcription, as well as a number of noncoding RNAs. A number of these genes represent potential targets for much-needed novel antifungal drugs.
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Novel genes retrieved from environmental DNA by polymerase chain reaction: current genome-walking techniques for future metagenome applications. J Biotechnol 2009; 144:75-82. [PMID: 19712711 DOI: 10.1016/j.jbiotec.2009.08.013] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2009] [Revised: 08/11/2009] [Accepted: 08/17/2009] [Indexed: 11/24/2022]
Abstract
Environmental DNA is an extremely rich source of genes encoding enzymes with novel biocatalytic activities. To tap this source, function-based and sequence-based strategies have been established to isolate, clone, and express these novel metagenome-derived genes. Sequence-based strategies, which rely on PCR with consensus primers and genome walking, represent an efficient and inexpensive alternative to activity-based screening of recombinant strains harbouring fragments of environmental DNA. This review covers the diverse array of genome-walking techniques, which were originally developed for genomic DNA and currently are also used for PCR-based recovery of entire genes from the metagenome. These sequence-based gene mining methods appear to offer a powerful tool for retrieving from the metagenome novel genes encoding biocatalysts with potential applications in biotechnology.
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41
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The electron transfer system of syntrophically grown Desulfovibrio vulgaris. J Bacteriol 2009; 191:5793-801. [PMID: 19581361 DOI: 10.1128/jb.00356-09] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Interspecies hydrogen transfer between organisms producing and consuming hydrogen promotes the decomposition of organic matter in most anoxic environments. Although syntrophic coupling between hydrogen producers and consumers is a major feature of the carbon cycle, mechanisms for energy recovery at the extremely low free energies of reactions typical of these anaerobic communities have not been established. In this study, comparative transcriptional analysis of a model sulfate-reducing microbe, Desulfovibrio vulgaris Hildenborough, suggested the use of alternative electron transfer systems dependent on growth modality. During syntrophic growth on lactate with a hydrogenotrophic methanogen, numerous genes involved in electron transfer and energy generation were upregulated in D. vulgaris compared with their expression in sulfate-limited monocultures. In particular, genes coding for the putative membrane-bound Coo hydrogenase, two periplasmic hydrogenases (Hyd and Hyn), and the well-characterized high-molecular-weight cytochrome (Hmc) were among the most highly expressed and upregulated genes. Additionally, a predicted operon containing genes involved in lactate transport and oxidation exhibited upregulation, further suggesting an alternative pathway for electrons derived from lactate oxidation during syntrophic growth. Mutations in a subset of genes coding for Coo, Hmc, Hyd, and Hyn impaired or severely limited syntrophic growth but had little effect on growth via sulfate respiration. These results demonstrate that syntrophic growth and sulfate respiration use largely independent energy generation pathways and imply that to understand microbial processes that sustain nutrient cycling, lifestyles not captured in pure culture must be considered.
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Characterization of a beta-glucoside operon (bgc) prevalent in septicemic and uropathogenic Escherichia coli strains. Appl Environ Microbiol 2009; 75:2284-93. [PMID: 19233952 DOI: 10.1128/aem.02621-08] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Escherichia coli strains, in general, do not ferment cellobiose and aryl-beta-D-glucosidic sugars, although "cryptic" beta-d-glucoside systems have been characterized. Here we describe an additional cryptic operon (bgc) for the utilization of cellobiose and the aryl-beta-d-glucosides arbutin and salicin at low temperature. The bgc operon was identified by the characterization of beta-glucoside-positive mutants of an E. coli septicemia strain (i484) in which the well-studied bgl (aryl-beta-d-glucoside) operon was deleted. These bgc* mutants appeared after 5 days of incubation on salicin indicator plates at 28 degrees C. The bgc operon codes for proteins homologous to beta-glucoside/cellobiose-specific phosphoenolpyruvate-dependent phosphotransfer system permease subunits IIB (BgcE), IIC (BgcF), and IIA (BgcI); a porin (BgcH); and a phospho-beta-D-glucosidase (BgcA). Next to the bgc operon maps the divergent bgcR gene, which encodes a GntR-type transcriptional regulator. Expression of the bgc operon is dependent on the cyclic-AMP-dependent regulator protein CRP and positively controlled by BgcR. In the bgc* mutants, a single nucleotide exchange enhances the activity of the bgc promoter, rendering it BgcR independent. Typing of a representative collection of E. coli demonstrated the prevalence of bgc in strains of phylogenetic group B2, representing mainly extraintestinal pathogens, while it is rare among commensal E. coli strains. The bgc locus is also present in the closely related species Escherichia albertii. Further, bioinformatic analyses demonstrated that homologs of the bgc genes exist in the enterobacterial Klebsiella, Enterobacter, and Citrobacter spp. and also in gram-positive bacteria, indicative of horizontal gene transfer events.
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Evolutionary history of the phl gene cluster in the plant-associated bacterium Pseudomonas fluorescens. Appl Environ Microbiol 2009; 75:2122-31. [PMID: 19181839 DOI: 10.1128/aem.02052-08] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas fluorescens is of agricultural and economic importance as a biological control agent largely because of its plant association and production of secondary metabolites, in particular 2,4-diacetylphloroglucinol (2,4-DAPG). This polyketide, which is encoded by the eight-gene phl cluster, has antimicrobial effects on phytopathogens, promotes amino acid exudation from plant roots, and induces systemic resistance in plants. Despite its importance, 2,4-DAPG production is limited to a subset of P. fluorescens strains. Determination of the evolution of the phl cluster and understanding the selective pressures promoting its retention or loss in lineages of P. fluorescens will help in the development of P. fluorescens as a viable and effective inoculant for application in agriculture. In this study, genomic and sequence-based approaches were integrated to reconstruct the phylogeny of P. fluorescens and the phl cluster. It was determined that 2,4-DAPG production is an ancestral trait in the species P. fluorescens but that most lineages have lost this capacity through evolution. Furthermore, intragenomic recombination has relocated the phl cluster within the P. fluorescens genome at least three times, but the integrity of the cluster has always been maintained. The possible evolutionary and functional implications for retention of the phl cluster and 2,4-DAPG production in some lineages of P. fluorescens are discussed.
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44
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Cloning and characterization of Plasmodium vivax serine hydroxymethyltransferase. Parasitol Int 2008; 57:223-8. [DOI: 10.1016/j.parint.2007.11.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 11/02/2007] [Accepted: 11/05/2007] [Indexed: 01/06/2023]
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45
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Reid AN, Pandey R, Palyada K, Whitworth L, Doukhanine E, Stintzi A. Identification of Campylobacter jejuni genes contributing to acid adaptation by transcriptional profiling and genome-wide mutagenesis. Appl Environ Microbiol 2008; 74:1598-612. [PMID: 18192408 PMCID: PMC2258640 DOI: 10.1128/aem.01508-07] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2007] [Accepted: 12/30/2007] [Indexed: 12/17/2022] Open
Abstract
In order to cause disease, the food- and waterborne pathogen Campylobacter jejuni must face the extreme acidity of the host stomach as well as cope with pH fluctuations in the intestine. In the present study, C. jejuni NCTC 11168 was grown under mildly acidic conditions mimicking those encountered in the intestine. The resulting transcriptional profiles revealed how this bacterium fine-tunes gene expression in response to acid stress. This adaptation involves the differential expression of respiratory pathways, the induction of genes for phosphate transport, and the repression of energy generation and intermediary metabolism genes. We also generated and screened a transposon-based mutant library to identify genes required for wild-type levels of growth under mildly acidic conditions. This screen highlighted the important role played by cell surface components (flagella, the outer membrane, capsular polysaccharides, and lipooligosaccharides) in the acid stress response of C. jejuni. Our data also revealed that a limited correlation exists between genes required for growth under acidic conditions and genes differentially expressed in response to acid. To gain a comprehensive picture of the acid stress response of C. jejuni, we merged transcriptional profiles obtained from acid-adapted cells and cells subjected to acid shock. Genes encoding the transcriptional regulator PerR and putative oxidoreductase subunits Cj0414 and Cj0415 were among the few up-regulated under both acid stress conditions. As a Cj0415 mutant was acid sensitive, it is likely that these genes are crucial to the acid stress response of C. jejuni and consequently are important for host colonization.
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Affiliation(s)
- Anne N Reid
- Ottawa Institute of Systems Biology, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada
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Abstract
The response of exponentially growing Desulfovibrio vulgaris Hildenborough to pH 10 stress was studied using oligonucleotide microarrays and a study set of mutants with genes suggested by microarray data to be involved in the alkaline stress response deleted. The data showed that the response of D. vulgaris to increased pH is generally similar to that of Escherichia coli but is apparently controlled by unique regulatory circuits since the alternative sigma factors (sigma S and sigma E) contributing to this stress response in E. coli appear to be absent in D. vulgaris. Genes previously reported to be up-regulated in E. coli were up-regulated in D. vulgaris; these genes included three ATPase genes and a tryptophan synthase gene. Transcription of chaperone and protease genes (encoding ATP-dependent Clp and La proteases and DnaK) was also elevated in D. vulgaris. As in E. coli, genes involved in flagellum synthesis were down-regulated. The transcriptional data also identified regulators, distinct from sigma S and sigma E, that are likely part of a D. vulgaris Hildenborough-specific stress response system. Characterization of a study set of mutants with genes implicated in alkaline stress response deleted confirmed that there was protective involvement of the sodium/proton antiporter NhaC-2, tryptophanase A, and two putative regulators/histidine kinases (DVU0331 and DVU2580).
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47
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Liang N, Wu H, Ye J, Xu P, Zhang Y, Zhang H. Molecular cloning of an insertion sequence-like element from Vibrio anguillarum and its functional identification in E. coli. Biotechnol Lett 2007; 29:1951-7. [PMID: 17823776 DOI: 10.1007/s10529-007-9485-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Revised: 07/03/2007] [Accepted: 07/05/2007] [Indexed: 11/30/2022]
Abstract
The tdh (thermostable direct hemolysin) gene occurs in some strains of Vibrio species. All tdh genes are flanked by insertion sequence-like elements (ISV). All previous attempts have failed to detect transposition of these ISVs. In this work, we have built a transposition detection system in E. coli and succeeded in detecting the transposition of an insertion sequence-like element at a frequency of Km(r) mutants of 7.2 x 10(-6). A specific flanking sequence (5'-Py-Pu-3') was found on either side of the target duplication.
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Affiliation(s)
- Na Liang
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, China
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48
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Abstract
The rapid expanse of microbial genome databases provides incentive and opportunity to study organismal behavior at the whole-genome level. While many newly sequenced genes are assigned names based on homology to previously characterized genes, many putative open reading frames remain to be annotated. The use of microarrays enables functional characterization of the entire genome with respect to genes important for different growth conditions including nutrient deprivation, stress responses, and virulence. The methods described here combine advancements in the identification of genomic sequences flanking insertional mutants with microarray methodology. The combination of these methods facilitates tracking large numbers of mutants for phenotypic studies. This improves both the efficiency of genome-saturating library screens and contributes to the functional annotation of unknown genes.
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Affiliation(s)
- David N Baldwin
- Human Biology Division, Fred Hutchinson Cancer Research Center, Seattle, WA, USA
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Thompson KM, Rhodius VA, Gottesman S. SigmaE regulates and is regulated by a small RNA in Escherichia coli. J Bacteriol 2007; 189:4243-56. [PMID: 17416652 PMCID: PMC1913397 DOI: 10.1128/jb.00020-07] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
RybB is a small, Hfq-binding noncoding RNA originally identified in a screen of conserved intergenic regions in Escherichia coli. Fusions of the rybB promoter to lacZ were used to screen plasmid genomic libraries and genomic transposon mutants for regulators of rybB expression. A number of plasmids, including some carrying rybB, negatively regulated the fusion. An insertion in the rep helicase and one upstream of dnaK decreased expression of the fusion. Multicopy suppressors of these insertions led to identification of two plasmids that stimulated the fusion. One contained the gene for the response regulator OmpR; the second contained mipA, encoding a murein hydrolase. The involvement of MipA and OmpR in cell surface synthesis suggested that the rybB promoter might be dependent on sigma(E). The sequence upstream of the +1 of rybB contains a consensus sigma(E) promoter. The activity of rybB-lacZ was increased in cells lacking the RseA anti-sigma factor and when sigma(E) was overproduced from a heterologous promoter. The activity of rybB-lacZ and the detection of RybB were totally abolished in an rpoE-null strain. In vitro, sigma(E) efficiently transcribes from this promoter. Both a rybB mutation and an hfq mutation significantly increased expression of both rybB-lacZ and rpoE-lacZ fusions, consistent with negative regulation of the sigma(E) response by RybB and other small RNAs. Based on the plasmid screens, NsrR, a repressor sensitive to nitric oxide, was also found to negatively regulate sigma(E)-dependent promoters in an RseA-independent fashion.
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Affiliation(s)
- Karl M Thompson
- Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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Maas MFPM, Hoekstra RF, Debets AJM. A mitochondrial mutator plasmid that causes senescence under dietary restricted conditions. BMC Genet 2007; 8:9. [PMID: 17407571 PMCID: PMC1864894 DOI: 10.1186/1471-2156-8-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Accepted: 04/02/2007] [Indexed: 11/25/2022] Open
Abstract
Background Calorie or dietary restriction extends life span in a wide range of organisms including the filamentous fungus Podospora anserina. Under dietary restricted conditions, P. anserina isolates are several-fold longer lived. This is however not the case in isolates that carry one of the pAL2-1 homologous mitochondrial plasmids. Results We show that the pAL2-1 homologues act as 'insertional mutators' of the mitochondrial genome, which may explain their negative effect on life span extension. Sequencing revealed at least fourteen unique plasmid integration sites, of which twelve were located within the mitochondrial genome and two within copies of the plasmid itself. The plasmids were able to integrate in their entirety, via a non-homologous mode of recombination. Some of the integrated plasmid copies were truncated, which probably resulted from secondary, post-integrative, recombination processes. Integration sites were predominantly located within and surrounding the region containing the mitochondrial rDNA loci. Conclusion We propose a model for the mechanism of integration, based on innate modes of mtDNA recombination, and discuss its possible link with the plasmid's negative effect on dietary restriction mediated life span extension.
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Affiliation(s)
- Marc FPM Maas
- Centre de Génétique Moléculaire, Centre Nationale de la Recherche Scientifique, 1 Avenue de la Terrasse, Gif-sur-Yvette, France
- Laboratorium voor Erfelijkheidsleer, Wageningen Universiteit, Arboretumlaan 4, Wageningen, The Netherlands
| | - Rolf F Hoekstra
- Laboratorium voor Erfelijkheidsleer, Wageningen Universiteit, Arboretumlaan 4, Wageningen, The Netherlands
| | - Alfons JM Debets
- Laboratorium voor Erfelijkheidsleer, Wageningen Universiteit, Arboretumlaan 4, Wageningen, The Netherlands
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