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Castro-Severyn J, Pardo-Esté C, Mendez KN, Morales N, Marquez SL, Molina F, Remonsellez F, Castro-Nallar E, Saavedra CP. Genomic Variation and Arsenic Tolerance Emerged as Niche Specific Adaptations by Different Exiguobacterium Strains Isolated From the Extreme Salar de Huasco Environment in Chilean - Altiplano. Front Microbiol 2020; 11:1632. [PMID: 32760381 PMCID: PMC7374977 DOI: 10.3389/fmicb.2020.01632] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 06/23/2020] [Indexed: 12/17/2022] Open
Abstract
Polyextremophilic bacteria can thrive in environments with multiple stressors such as the Salar de Huasco (SH). Microbial communities in SH are exposed to low atmospheric pressure, high UV radiation, wide temperature ranges, salinity gradient and the presence of toxic compounds such as arsenic (As). In this work we focus on arsenic stress as one of the main adverse factors in SH and bacteria that belong to the Exiguobacterium genus due to their plasticity and ubiquity. Therefore, our aim was to shed light on the effect of niche conditions pressure (particularly arsenic), on the adaptation and divergence (at genotypic and phenotypic levels) of Exiguobacterium strains from five different SH sites. Also, to capture greater diversity in this genus, we use as outgroup five As(III) sensitive strains isolated from Easter Island (Chile) and The Great Salt Lake (United States). For this, samples were obtained from five different SH sites under an arsenic gradient (9 to 321 mg/kg: sediment) and isolated and sequenced the genomes of 14 Exiguobacterium strains, which had different arsenic tolerance levels. Then, we used comparative genomic analysis to assess the genomic divergence of these strains and their association with phenotypic differences such as arsenic tolerance levels and the ability to resist poly-stress. Phylogenetic analysis showed that SH strains share a common ancestor. Consequently, populations were separated and structured in different SH microenvironments, giving rise to multiple coexisting lineages. Hence, this genotypic variability is also evidenced by the COG (Clusters of Orthologous Groups) composition and the size of their accessory genomes. Interestingly, these observations correlate with physiological traits such as growth patterns, gene expression, and enzyme activity related to arsenic response and/or tolerance. Therefore, Exiguobacterium strains from SH are adapted to physiologically overcome the contrasting environmental conditions, like the arsenic present in their habitat.
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Affiliation(s)
- Juan Castro-Severyn
- Laboratorio de Microbiología Aplicada y Extremófilos, Facultad de Ingeniería y Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile.,Laboratorio de Microbiología Molecular, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
| | - Coral Pardo-Esté
- Laboratorio de Microbiología Molecular, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
| | - Katterinne N Mendez
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
| | - Naiyulin Morales
- Laboratorio de Microbiología Molecular, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
| | - Sebastián L Marquez
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
| | - Franck Molina
- Sys2Diag CNRS/Alcediag, CNRS UMR 3145, Montpellier, France
| | - Francisco Remonsellez
- Laboratorio de Microbiología Aplicada y Extremófilos, Facultad de Ingeniería y Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile.,Centro de Investigación Tecnológica del Agua en el Desierto-CEITSAZA, Universidad Católica del Norte, Antofagasta, Chile
| | - Eduardo Castro-Nallar
- Center for Bioinformatics and Integrative Biology, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
| | - Claudia P Saavedra
- Laboratorio de Microbiología Molecular, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
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Yang Y, Wang J, Zhang R, Yan Y. Antisense RNA Elements for Downregulating Expression. Methods Mol Biol 2019; 1927:23-35. [PMID: 30788783 DOI: 10.1007/978-1-4939-9142-6_3] [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] [Indexed: 06/09/2023]
Abstract
Antisense RNA (asRNA) technology is an important tool for downregulating gene expression. When applying this strategy, the asRNA interference efficiency is determined by several elements including scaffold design, loop size, and relative abundance. Here, we take the Escherichia coli gene fabD encoding malonyl-CoA-[acyl-carrier-protein] transacylase as an example to describe the asRNA design with reliable and controllable interference efficiency. Real-time PCR and fluorescence assay methods are introduced to detect the interference efficiency at RNA level and protein level, respectively.
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Affiliation(s)
- Yaping Yang
- College of Engineering, University of Georgia, Athens, GA, USA
| | - Jian Wang
- College of Engineering, University of Georgia, Athens, GA, USA
| | - Ruihua Zhang
- College of Engineering, University of Georgia, Athens, GA, USA
| | - Yajun Yan
- School of Chemical, Materials and Biomedical Engineering, College of Engineering, University of Georgia, Athens, GA, USA.
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Bageshwar UK, VerPlank L, Baker D, Dong W, Hamsanathan S, Whitaker N, Sacchettini JC, Musser SM. High Throughput Screen for Escherichia coli Twin Arginine Translocation (Tat) Inhibitors. PLoS One 2016; 11:e0149659. [PMID: 26901445 PMCID: PMC4764201 DOI: 10.1371/journal.pone.0149659] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 02/03/2016] [Indexed: 01/29/2023] Open
Abstract
The twin arginine translocation (Tat) pathway transports fully-folded and assembled proteins in bacteria, archaea and plant thylakoids. The Tat pathway contributes to the virulence of numerous bacterial pathogens that cause disease in humans, cattle and poultry. Thus, the Tat pathway has the potential to be a novel therapeutic target. Deciphering the Tat protein transport mechanism has been challenging since the active translocon only assembles transiently in the presence of substrate and a proton motive force. To identify inhibitors of Tat transport that could be used as biochemical tools and possibly as drug development leads, we developed a high throughput screen (HTS) to assay the effects of compounds in chemical libraries against protein export by the Escherichia coli Tat pathway. The primary screen is a live cell assay based on a fluorescent Tat substrate that becomes degraded in the cytoplasm when Tat transport is inhibited. Consequently, low fluorescence in the presence of a putative Tat inhibitor was scored as a hit. Two diverse chemical libraries were screened, yielding average Z'-factors of 0.74 and 0.44, and hit rates of ~0.5% and 0.04%, respectively. Hits were evaluated by a series of secondary screens. Electric field gradient (Δψ) measurements were particularly important since the bacterial Tat transport requires a Δψ. Seven low IC50 hits were eliminated by Δψ assays, suggesting ionophore activity. As Δψ collapse is generally toxic to animal cells and efficient membrane permeability is generally favored during the selection of library compounds, these results suggest that secondary screening of hits against electrochemical effects should be done early during hit validation. Though none of the short-listed compounds inhibited Tat transport directly, the screening and follow-up assays developed provide a roadmap to pursue Tat transport inhibitors.
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Affiliation(s)
- Umesh K. Bageshwar
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX, United States of America
| | - Lynn VerPlank
- Broad Institute, Cambridge, MA, United States of America
| | - Dwight Baker
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, United States of America
| | - Wen Dong
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, United States of America
| | - Shruthi Hamsanathan
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX, United States of America
| | - Neal Whitaker
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX, United States of America
| | - James C. Sacchettini
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, United States of America
| | - Siegfried M. Musser
- Department of Molecular and Cellular Medicine, College of Medicine, Texas A&M Health Science Center, College Station, TX, United States of America
- * E-mail:
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Low-temperature biosynthesis of fluorescent semiconductor nanoparticles (CdS) by oxidative stress resistant Antarctic bacteria. J Biotechnol 2014; 187:108-15. [DOI: 10.1016/j.jbiotec.2014.07.017] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2014] [Revised: 07/08/2014] [Accepted: 07/12/2014] [Indexed: 12/20/2022]
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Fuciños P, Atanes E, López-López O, Solaroli M, Cerdán ME, González-Siso MI, Pastrana L, Rúa ML. Cloning, expression, purification and characterization of an oligomeric His-tagged thermophilic esterase from Thermus thermophilus HB27. Process Biochem 2014. [DOI: 10.1016/j.procbio.2014.03.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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Putative Inv is essential for basolateral invasion of Caco-2 cells and acts synergistically with OmpA to affect in vitro and in vivo virulence of Cronobacter sakazakii ATCC 29544. Infect Immun 2014; 82:1755-65. [PMID: 24549330 DOI: 10.1128/iai.01397-13] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Cronobacter sakazakii is an opportunistic pathogen that causes neonatal meningitis and necrotizing enterocolitis. Its interaction with intestinal epithelium is important in the pathogenesis of enteric infections. In this study, we investigated the involvement of the inv gene in the virulence of C. sakazakii ATCC 29544 in vitro and in vivo. Sequence analysis of C. sakazakii ATCC 29544 inv revealed that it is different from other C. sakazakii isolates. In various cell culture models, an Δinv deletion mutant showed significantly lowered invasion efficiency, which was restored upon genetic complementation. Studying invasion potentials using tight-junction-disrupted Caco-2 cells suggested that the inv gene product mediates basolateral invasion of C. sakazakii ATCC 29544. In addition, comparison of invasion potentials of double mutant (ΔompA Δinv) and single mutants (ΔompA and Δinv) provided evidence for an additive effect of the two putative outer membrane proteins. Finally, the importance of inv and the additive effect of putative Inv and OmpA were also proven in an in vivo rat pup model. This report is the first to demonstrate two proteins working synergistically in vitro, as well as in vivo in C. sakazakii pathogenesis.
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Ji Y, Lei T. Antisense RNA regulation and application in the development of novel antibiotics to combat multidrug resistant bacteria. Sci Prog 2013; 96:43-60. [PMID: 23738437 PMCID: PMC10365521 DOI: 10.3184/003685013x13617194309028] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Despite the availability of antibiotics and vaccines, infectious diseases remain one of most dangerous threats to humans and animals. The overuse and misuse of antibacterial agents have led to the emergence of multidrug resistant bacterial pathogens. Bacterial cells are often resilient enough to survive in even the most extreme environments. To do so, the organisms have evolved different mechanisms, including a variety of two-component signal transduction systems, which allow the bacteria to sense the surrounding environment and regulate gene expression in order to adapt and respond to environmental stimuli. In addition, some bacteria evolve resistance to antibacterial agents while many bacterial cells are able to acquire resistance genes from other bacterial species to enable them to survive in the presence of toxic antimicrobial agents. The crisis of antimicrobial resistance is an unremitting menace to human health and a burden on public health. The rapid increase in antimicrobial resistant organisms and limited options for development of new classes of antibiotics heighten the urgent need to develop novel potent antibacterial therapeutics in order to combat multidrug resistant infections. In this review, we introduce the regulatory mechanisms of antisense RNA and significant applications of regulated antisense RNA interference technology in early drug discovery. This includes the identification and evaluation of drug targets in vitro and in vivo, the determination of mode of action for antibiotics and new antibacterial agents, as well as the development of peptide-nucleic acid conjugates as novel antibacterials.
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Akhova AV, Tkachenko AG. Lysine decarboxylase activity as a factor of fluoroquinolone resistance in Escherichia coli. Microbiology (Reading) 2009. [DOI: 10.1134/s0026261709050075] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Woodford N, Wareham DW. Tackling antibiotic resistance: a dose of common antisense? J Antimicrob Chemother 2008; 63:225-9. [DOI: 10.1093/jac/dkn467] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
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Rasmussen LCV, Sperling-Petersen HU, Mortensen KK. Hitting bacteria at the heart of the central dogma: sequence-specific inhibition. Microb Cell Fact 2007; 6:24. [PMID: 17692125 PMCID: PMC1995221 DOI: 10.1186/1475-2859-6-24] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Accepted: 08/10/2007] [Indexed: 12/16/2022] Open
Abstract
An important objective in developing new drugs is the achievement of high specificity to maximize curing effect and minimize side-effects, and high specificity is an integral part of the antisense approach. The antisense techniques have been extensively developed from the application of simple long, regular antisense RNA (asRNA) molecules to highly modified versions conferring resistance to nucleases, stability of hybrid formation and other beneficial characteristics, though still preserving the specificity of the original nucleic acids. These new and improved second- and third-generation antisense molecules have shown promising results. The first antisense drug has been approved and more are in clinical trials. However, these antisense drugs are mainly designed for the treatment of different human cancers and other human diseases. Applying antisense gene silencing and exploiting RNA interference (RNAi) are highly developed approaches in many eukaryotic systems. But in bacteria RNAi is absent, and gene silencing by antisense compounds is not nearly as well developed, despite its great potential and the intriguing possibility of applying antisense molecules in the fight against multiresistant bacteria. Recent breakthrough and current status on the development of antisense gene silencing in bacteria including especially phosphorothioate oligonucleotides (PS-ODNs), peptide nucleic acids (PNAs) and phosphorodiamidate morpholino oligomers (PMOs) will be presented in this review.
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Affiliation(s)
| | - Hans Uffe Sperling-Petersen
- Laboratory of BioDesign, Department of Molecular Biology, Aarhus University, Gustav Wieds Vej 10 C, DK-8000 Aarhus C, Denmark
| | - Kim Kusk Mortensen
- Laboratory of BioDesign, Department of Molecular Biology, Aarhus University, Gustav Wieds Vej 10 C, DK-8000 Aarhus C, Denmark
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Pérez JM, Calderón IL, Arenas FA, Fuentes DE, Pradenas GA, Fuentes EL, Sandoval JM, Castro ME, Elías AO, Vásquez CC. Bacterial toxicity of potassium tellurite: unveiling an ancient enigma. PLoS One 2007; 2:e211. [PMID: 17299591 PMCID: PMC1784070 DOI: 10.1371/journal.pone.0000211] [Citation(s) in RCA: 153] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Accepted: 01/22/2007] [Indexed: 11/19/2022] Open
Abstract
Biochemical, genetic, enzymatic and molecular approaches were used to demonstrate, for the first time, that tellurite (TeO32−) toxicity in E. coli involves superoxide formation. This radical is derived, at least in part, from enzymatic TeO32− reduction. This conclusion is supported by the following observations made in K2TeO3-treated E. coli BW25113: i) induction of the ibpA gene encoding for the small heat shock protein IbpA, which has been associated with resistance to superoxide, ii) increase of cytoplasmic reactive oxygen species (ROS) as determined with ROS-specific probe 2′7′-dichlorodihydrofluorescein diacetate (H2DCFDA), iii) increase of carbonyl content in cellular proteins, iv) increase in the generation of thiobarbituric acid-reactive substances (TBARs), v) inactivation of oxidative stress-sensitive [Fe-S] enzymes such as aconitase, vi) increase of superoxide dismutase (SOD) activity, vii) increase of sodA, sodB and soxS mRNA transcription, and viii) generation of superoxide radical during in vitro enzymatic reduction of potassium tellurite.
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Affiliation(s)
- José M. Pérez
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Iván L. Calderón
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Felipe A. Arenas
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Derie E. Fuentes
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Gonzalo A. Pradenas
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Eugenia L. Fuentes
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Juan M. Sandoval
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Miguel E. Castro
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Alex O. Elías
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Claudio C. Vásquez
- Laboratorio de Microbiología Molecular, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
- * To whom correspondence should be addressed. E-mail:
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Liang X, Ji Y. Alpha-toxin interferes with integrin-mediated adhesion and internalization of Staphylococcus aureus by epithelial cells. Cell Microbiol 2006; 8:1656-68. [PMID: 16984420 DOI: 10.1111/j.1462-5822.2006.00740.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Staphylococcus aureus is an important human and animal pathogen. During infection, this bacterium is able to attach to and enter host cells by using its cell surface-associated factors to bind to the host's extracellular matrix (ECM) proteins. In this study, we determined that a protein exported by S. aureus, alpha-toxin, can interfere with the integrin-mediated adhesion and internalization of S. aureus by human lung epithelial cells (A549). The downregulation of alpha-toxin production significantly increased bacterial adhesion and invasion into the epithelial cells. In contrast, bacterial adhesion and invasion was inhibited by both overproduction of alpha-toxin and the addition of alpha-toxin to the culture medium. Moreover, our results showed that the quantitative effects on invasion closely parallel those of adherence. This suggests that the effect on invasion is probably secondary to, and a consequence of, the reduced adherence caused by alpha-toxin exposure. Specifically, we demonstrated that alpha-toxin interacts with the hosts' ECM protein's receptor, beta1-integrin, which indicates that beta1-integrin may be a potential receptor of alpha-toxin on epithelial cells. Taken together, our results indicate that exported alpha-toxin inhibits the adhesion and internalization of S. aureus by interfering with integrin-mediated pathogen-host cell interactions.
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Affiliation(s)
- Xudong Liang
- Department of Veterinary and Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108, USA
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Tkachenko AG, Pozhidaeva ON, Shumkov MS. Role of polyamines in formation of multiple antibiotic resistance of Escherichia coli under stress conditions. BIOCHEMISTRY (MOSCOW) 2006; 71:1042-9. [PMID: 17009960 DOI: 10.1134/s0006297906090148] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Under stress conditions, polyamines decreased the permeability of the outer membrane of Escherichia coli. This effect is caused by at least three mechanisms providing for an increase in the resistance to antibiotics transported through porin channels (fluoroquinolones, beta-lactams): a positive modulation of the gene micF transcription (its product antisense RNA inhibits the synthesis of porin proteins on the translational level); a positive effect on the cell content of the multiple stress resistance factor sigma(S) (it is accompanied by a decrease in the porin transport because of suppression of ompF transcription and induction of cadaverine synthesis); a direct inhibition of the transport activity of porin channels. The production of cadaverine in E. coli cells significantly increased in response to various antibiotics, and this was likely to be a manifestation of oxidative stress.
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Affiliation(s)
- A G Tkachenko
- Institute of Ecology and Genetics of Microorganisms, Ural Division, Russian Academy of Sciences, Perm 614081, Russia.
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Tkachenko AG, Shumkov MS, Akhova AV. Putrescine as a modulator of the level of RNA polymerase σS subunit in Escherichia coli cells under acid stress. BIOCHEMISTRY (MOSCOW) 2006; 71:185-93. [PMID: 16489924 DOI: 10.1134/s0006297906020118] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Metabolites accumulated in the culture medium of Escherichia coli cells induce expression of the rpoS gene encoding the alternative sigmaS subunit of RNA polymerase, which controls adaptation of E. coli to acid stress during growth in glucose-mineral medium. The effect of acetate and succinate as end products of E. coli metabolism has been investigated on the levels of transcription, translation, and sigmaS protein stability. These end products mainly influenced the stability of the RNA polymerase sigmaS subunit. Under conditions of acid stress caused by acetate addition, the content of polyamines in the cells and medium decreased, whereas artificial rpoS gene switch-off by antisense RNA was accompanied by increase in polyamine level. Addition of polyamine to E. coli cells treated with acetate and especially with succinate caused a significant concentration-dependent stimulatory effect on rpoS expression. Thus, induction of the rpoS regulon depends on the combined action of the investigated metabolites determining adequate control of gene expression under conditions of acid stress. A scheme for metabolic pathways describing the role of putrescine in the maintenance of intracellular pH and polyamine pool homeostasis during E. coli adaptation to acid stress is proposed.
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Affiliation(s)
- A G Tkachenko
- Institute of Ecology and Genetics of Microorganisms, Ural Branch of the Russian Academy of Sciences, 614081 Perm, Russia.
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