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Shore SFH, Leinberger FH, Fozo EM, Berghoff BA. Type I toxin-antitoxin systems in bacteria: from regulation to biological functions. EcoSal Plus 2024:eesp00252022. [PMID: 38767346 DOI: 10.1128/ecosalplus.esp-0025-2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Accepted: 04/11/2024] [Indexed: 05/22/2024]
Abstract
Toxin-antitoxin systems are ubiquitous in the prokaryotic world and widely distributed among chromosomes and mobile genetic elements. Several different toxin-antitoxin system types exist, but what they all have in common is that toxin activity is prevented by the cognate antitoxin. In type I toxin-antitoxin systems, toxin production is controlled by an RNA antitoxin and by structural features inherent to the toxin messenger RNA. Most type I toxins are small membrane proteins that display a variety of cellular effects. While originally discovered as modules that stabilize plasmids, chromosomal type I toxin-antitoxin systems may also stabilize prophages, or serve important functions upon certain stress conditions and contribute to population-wide survival strategies. Here, we will describe the intricate RNA-based regulation of type I toxin-antitoxin systems and discuss their potential biological functions.
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Affiliation(s)
- Selene F H Shore
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA
| | - Florian H Leinberger
- Institute for Microbiology and Molecular Biology, Justus-Liebig University, Giessen, Germany
| | - Elizabeth M Fozo
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA
| | - Bork A Berghoff
- Institute for Microbiology and Molecular Biology, Justus-Liebig University, Giessen, Germany
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2
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Lara Ortiz MT, Martinell García V, Del Rio G. Saturation Mutagenesis of the Transmembrane Region of HokC in Escherichia coli Reveals Its High Tolerance to Mutations. Int J Mol Sci 2021; 22:ijms221910359. [PMID: 34638709 PMCID: PMC8509063 DOI: 10.3390/ijms221910359] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 09/20/2021] [Accepted: 09/22/2021] [Indexed: 11/16/2022] Open
Abstract
Cells adapt to different stress conditions, such as the antibiotics presence. This adaptation sometimes is achieved by changing relevant protein positions, of which the mutability is limited by structural constrains. Understanding the basis of these constrains represent an important challenge for both basic science and potential biotechnological applications. To study these constraints, we performed a systematic saturation mutagenesis of the transmembrane region of HokC, a toxin used by Escherichia coli to control its own population, and observed that 92% of single-point mutations are tolerated and that all the non-tolerated mutations have compensatory mutations that reverse their effect. We provide experimental evidence that HokC accumulates multiple compensatory mutations that are found as correlated mutations in the HokC family multiple sequence alignment. In agreement with these observations, transmembrane proteins show higher probability to present correlated mutations and are less densely packed locally than globular proteins; previous mutagenesis results on transmembrane proteins further support our observations on the high tolerability to mutations of transmembrane regions of proteins. Thus, our experimental results reveal the HokC transmembrane region high tolerance to loss-of-function mutations that is associated with low sequence conservation and high rate of correlated mutations in the HokC family sequences alignment, which are features shared with other transmembrane proteins.
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3
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Mageiros L, Méric G, Bayliss SC, Pensar J, Pascoe B, Mourkas E, Calland JK, Yahara K, Murray S, Wilkinson TS, Williams LK, Hitchings MD, Porter J, Kemmett K, Feil EJ, Jolley KA, Williams NJ, Corander J, Sheppard SK. Genome evolution and the emergence of pathogenicity in avian Escherichia coli. Nat Commun 2021; 12:765. [PMID: 33536414 PMCID: PMC7858641 DOI: 10.1038/s41467-021-20988-w] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 01/04/2021] [Indexed: 01/30/2023] Open
Abstract
Chickens are the most common birds on Earth and colibacillosis is among the most common diseases affecting them. This major threat to animal welfare and safe sustainable food production is difficult to combat because the etiological agent, avian pathogenic Escherichia coli (APEC), emerges from ubiquitous commensal gut bacteria, with no single virulence gene present in all disease-causing isolates. Here, we address the underlying evolutionary mechanisms of extraintestinal spread and systemic infection in poultry. Combining population scale comparative genomics and pangenome-wide association studies, we compare E. coli from commensal carriage and systemic infections. We identify phylogroup-specific and species-wide genetic elements that are enriched in APEC, including pathogenicity-associated variation in 143 genes that have diverse functions, including genes involved in metabolism, lipopolysaccharide synthesis, heat shock response, antimicrobial resistance and toxicity. We find that horizontal gene transfer spreads pathogenicity elements, allowing divergent clones to cause infection. Finally, a Random Forest model prediction of disease status (carriage vs. disease) identifies pathogenic strains in the emergent ST-117 poultry-associated lineage with 73% accuracy, demonstrating the potential for early identification of emergent APEC in healthy flocks.
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Affiliation(s)
- Leonardos Mageiros
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
| | - Guillaume Méric
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
| | - Sion C Bayliss
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
- MRC Cloud Infrastructure for Microbial Bioinformatics (CLIMB) Consortium, London, UK
| | - Johan Pensar
- Department of Biostatistics, University of Oslo, Oslo, Norway
- Department of Mathematics and Statistics, Helsinki Institute for Information Technology, University of Helsinki, Helsinki, Finland
| | - Ben Pascoe
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
- Department of Biostatistics, University of Oslo, Oslo, Norway
| | - Evangelos Mourkas
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
| | - Jessica K Calland
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
| | - Koji Yahara
- Antimicrobial Resistance Research Centre, National Institute of Infectious Diseases, Tokyo, Japan
| | - Susan Murray
- Uppsala University, Department for medical biochemistry and microbiology, Uppsala University, Uppsala, Sweden
| | - Thomas S Wilkinson
- Swansea University Medical School, Institute of Life Science, Swansea, SA2 8PP, UK
| | - Lisa K Williams
- Swansea University Medical School, Institute of Life Science, Swansea, SA2 8PP, UK
| | - Matthew D Hitchings
- Swansea University Medical School, Institute of Life Science, Swansea, SA2 8PP, UK
| | - Jonathan Porter
- National Laboratory Service, Environment Agency, Starcross, UK
| | - Kirsty Kemmett
- Department of Epidemiology and Population Health, Institute of Infection & Global Health, University of Liverpool, Leahurst Campus, Wirral, UK
| | - Edward J Feil
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK
| | - Keith A Jolley
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
| | - Nicola J Williams
- Department of Epidemiology and Population Health, Institute of Infection & Global Health, University of Liverpool, Leahurst Campus, Wirral, UK
| | - Jukka Corander
- Department of Biostatistics, University of Oslo, Oslo, Norway
- Department of Mathematics and Statistics, Helsinki Institute for Information Technology, University of Helsinki, Helsinki, Finland
- Parasites and Microbes, Wellcome Sanger Institute, Cambridge, UK
| | - Samuel K Sheppard
- The Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, UK.
- MRC Cloud Infrastructure for Microbial Bioinformatics (CLIMB) Consortium, London, UK.
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
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Functional characterization of the type I toxin Lpt from Lactobacillus rhamnosus by fluorescence and atomic force microscopy. Sci Rep 2019; 9:15208. [PMID: 31645607 PMCID: PMC6811638 DOI: 10.1038/s41598-019-51523-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 09/30/2019] [Indexed: 01/22/2023] Open
Abstract
Lpt is a 29 amino acid long type I toxin identified in the plasmid DNA of wild Lactobacillus rhamnosus strains isolated from food. We previously reported that transcription of the encoding gene was upregulated under nutritional starvation conditions mimicking cheese ripening environment. The heterologous expression of the Lpt peptide in E. coli resulted in cell growth inhibition, nucleoid condensation and compromised integrity of the cell membrane. Fusion of the Lpt peptide with the fluorescent protein mCherry allowed to visualize the accumulation of the peptide into the membrane, while mutagenesis experiments showed that either the insertion of a negatively charged amino acid into the hydrophobic α-helix or deletion of the hydrophilic C-terminal region, leads to a non-toxic peptide. AFM imaging of Lpt expressing E. coli cells has revealed the presence of surface defects that are compatible with the loss of portions of the outer membrane bilayer. This observation provides support for the so-called “carpet” model, by which the Lpt peptide is supposed to destabilize the phospholipid packing through a detergent-like mechanism leading to the removal of small patches of bilayer through micellization.
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Chromosomally Encoded hok-sok Toxin-Antitoxin System in the Fire Blight Pathogen Erwinia amylovora: Identification and Functional Characterization. Appl Environ Microbiol 2019; 85:AEM.00724-19. [PMID: 31101613 DOI: 10.1128/aem.00724-19] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Accepted: 05/08/2019] [Indexed: 12/28/2022] Open
Abstract
Toxin-antitoxin (TA) systems are genetic elements composed of a protein toxin and a counteracting antitoxin that is either a noncoding RNA or protein. In type I TA systems, the antitoxin is a noncoding small RNA (sRNA) that base pairs with the cognate toxin mRNA interfering with its translation. Although type I TA systems have been extensively studied in Escherichia coli and a few human or animal bacterial pathogens, they have not been characterized in plant-pathogenic bacteria. In this study, we characterized a chromosomal locus in the plant pathogen Erwinia amylovora Ea1189 that is homologous to the hok-sok type I TA system previously identified in the Enterobacteriaceae-restricted plasmid R1. Phylogenetic analysis indicated that the chromosomal location of the hok-sok locus is, thus far, unique to E. amylovora We demonstrated that ectopic overexpression of hok is highly toxic to E. amylovora and that the sRNA sok reversed the toxicity of hok through mok, a reading frame presumably translationally coupled with hok We also identified the region that is essential for maintenance of the main toxicity of Hok. Through a hok-sok deletion mutant (Ea1189Δhok-sok), we determined the contribution of the hok-sok locus to cellular growth, micromorphology, and catalase activity. Combined, our findings indicate that the hok-sok TA system, besides being potentially self-toxic, provides fitness advantages to E. amylovora IMPORTANCE Bacterial toxin-antitoxin systems have received great attention because of their potential as targets for antimicrobial development and as tools for biotechnology. Erwinia amylovora, the causal agent of fire blight disease on pome fruit trees, is a major plant-pathogenic bacterium. In this study, we identified and functionally characterized a unique chromosomally encoded hok-sok toxin-antitoxin system in E. amylovora that resembles the plasmid-encoded copies of this system in other Enterobacteriaceae This study of a type I toxin-antitoxin system in a plant-pathogenic bacterium provides the basis to further understand the involvement of toxin-antitoxin systems during infection by a plant-pathogenic bacterium. The new linkage between the hok-sok toxin-antitoxin system and the catalase-mediated oxidative stress response leads to additional considerations of targeting this system for antimicrobial development.
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Next-generation biocontainment systems for engineered organisms. Nat Chem Biol 2018; 14:530-537. [PMID: 29769737 DOI: 10.1038/s41589-018-0056-x] [Citation(s) in RCA: 120] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 03/09/2018] [Indexed: 12/14/2022]
Abstract
The increasing use of engineered organisms for industrial, clinical, and environmental applications poses a growing risk of spreading hazardous biological entities into the environment. To address this biosafety issue, significant effort has been invested in creating ways to confine these organisms and transgenic materials. Emerging technologies in synthetic biology involving genetic circuit engineering, genome editing, and gene expression regulation have led to the development of novel biocontainment systems. In this perspective, we highlight recent advances in biocontainment and suggest a number of approaches for future development, which may be applied to overcome remaining challenges in safeguard implementation.
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Low escape-rate genome safeguards with minimal molecular perturbation of Saccharomyces cerevisiae. Proc Natl Acad Sci U S A 2017; 114:E1470-E1479. [PMID: 28174266 DOI: 10.1073/pnas.1621250114] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
As the use of synthetic biology both in industry and in academia grows, there is an increasing need to ensure biocontainment. There is growing interest in engineering bacterial- and yeast-based safeguard (SG) strains. First-generation SGs were based on metabolic auxotrophy; however, the risk of cross-feeding and the cost of growth-controlling nutrients led researchers to look for other avenues. Recent strategies include bacteria engineered to be dependent on nonnatural amino acids and yeast SG strains that have both transcriptional- and recombinational-based biocontainment. We describe improving yeast Saccharomyces cerevisiae-based transcriptional SG strains, which have near-WT fitness, the lowest possible escape rate, and nanomolar ligands controlling growth. We screened a library of essential genes, as well as the best-performing promoter and terminators, yielding the best SG strains in yeast. The best constructs were fine-tuned, resulting in two tightly controlled inducible systems. In addition, for potential use in the prevention of industrial espionage, we screened an array of possible "decoy molecules" that can be used to mask any proprietary supplement to the SG strain, with minimal effect on strain fitness.
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Brielle R, Pinel-Marie ML, Felden B. Linking bacterial type I toxins with their actions. Curr Opin Microbiol 2016; 30:114-121. [PMID: 26874964 DOI: 10.1016/j.mib.2016.01.009] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2015] [Revised: 01/18/2016] [Accepted: 01/19/2016] [Indexed: 01/12/2023]
Abstract
Bacterial type I toxin-antitoxin systems consist of stable toxin-encoding mRNAs whose expression is counteracted by unstable RNA antitoxins. Accumulating evidence suggests that these players belong to broad regulatory networks influencing overall bacterial physiology. The majority of known transmembrane type I toxic peptides have conserved structural characteristics. However, recent studies demonstrated that their mechanisms of toxicity are diverse and complex. To better assess the current state of the art, type I toxins can be grouped into two classes according to their location and mechanisms of action: membrane-associated toxins acting by pore formation and/or by nucleoid condensation; and cytosolic toxins inducing nucleic acid cleavage. This classification will evolve as a result of future investigations.
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Affiliation(s)
- Régine Brielle
- Inserm U835-Upres EA2311, Pharmaceutical Biochemistry Lab, University of Rennes 1, 2 av. du Prof. Léon Bernard, 35000 Rennes, France
| | - Marie-Laure Pinel-Marie
- Inserm U835-Upres EA2311, Pharmaceutical Biochemistry Lab, University of Rennes 1, 2 av. du Prof. Léon Bernard, 35000 Rennes, France.
| | - Brice Felden
- Inserm U835-Upres EA2311, Pharmaceutical Biochemistry Lab, University of Rennes 1, 2 av. du Prof. Léon Bernard, 35000 Rennes, France.
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9
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Ortiz MTL, Rosario PBL, Luna-Nevarez P, Gamez AS, Martínez-del Campo A, Del Rio G. Quality control test for sequence-phenotype assignments. PLoS One 2015; 10:e0118288. [PMID: 25700273 PMCID: PMC4336291 DOI: 10.1371/journal.pone.0118288] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Accepted: 12/22/2014] [Indexed: 11/18/2022] Open
Abstract
Relating a gene mutation to a phenotype is a common task in different disciplines such as protein biochemistry. In this endeavour, it is common to find false relationships arising from mutations introduced by cells that may be depurated using a phenotypic assay; yet, such phenotypic assays may introduce additional false relationships arising from experimental errors. Here we introduce the use of high-throughput DNA sequencers and statistical analysis aimed to identify incorrect DNA sequence-phenotype assignments and observed that 10–20% of these false assignments are expected in large screenings aimed to identify critical residues for protein function. We further show that this level of incorrect DNA sequence-phenotype assignments may significantly alter our understanding about the structure-function relationship of proteins. We have made available an implementation of our method at http://bis.ifc.unam.mx/en/software/chispas.
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Affiliation(s)
- Maria Teresa Lara Ortiz
- Department of Biochemistry and Structural Biology. Instituto de Fisiología Celular at the Universidad Nacional Autónoma de México, México DF, 04510, México
| | - Pablo Benjamín Leon Rosario
- Department of Biochemistry and Structural Biology. Instituto de Fisiología Celular at the Universidad Nacional Autónoma de México, México DF, 04510, México
| | - Pablo Luna-Nevarez
- Department of agronomical sciences and veterinary. Sonora Institute of Technology, Obregon city 85000, Mexico
| | - Alba Savin Gamez
- Department of Biochemistry and Structural Biology. Instituto de Fisiología Celular at the Universidad Nacional Autónoma de México, México DF, 04510, México
| | - Ana Martínez-del Campo
- Department of Genetics. Instituto de Fisiología Celular at the Universidad Nacional Autónoma de México, México DF, 04510, México
| | - Gabriel Del Rio
- Department of Biochemistry and Structural Biology. Instituto de Fisiología Celular at the Universidad Nacional Autónoma de México, México DF, 04510, México
- * E-mail:
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Intrinsic biocontainment: multiplex genome safeguards combine transcriptional and recombinational control of essential yeast genes. Proc Natl Acad Sci U S A 2015; 112:1803-8. [PMID: 25624482 DOI: 10.1073/pnas.1424704112] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Biocontainment may be required in a wide variety of situations such as work with pathogens, field release applications of engineered organisms, and protection of intellectual properties. Here, we describe the control of growth of the brewer's yeast, Saccharomyces cerevisiae, using both transcriptional and recombinational "safeguard" control of essential gene function. Practical biocontainment strategies dependent on the presence of small molecules require them to be active at very low concentrations, rendering them inexpensive and difficult to detect. Histone genes were controlled by an inducible promoter and controlled by 30 nM estradiol. The stability of the engineered genes was separately regulated by the expression of a site-specific recombinase. The combined frequency of generating viable derivatives when both systems were active was below detection (<10(-10)), consistent with their orthogonal nature and the individual escape frequencies of <10(-6). Evaluation of escaper mutants suggests strategies for reducing their emergence. Transcript profiling and growth test suggest high fitness of safeguarded strains, an important characteristic for wide acceptance.
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11
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Shin D, Nam K. Potential use of a self-dying reporter bacterium to determine the bioavailability of aged phenanthrene in soil: comparison with physicochemical measures. JOURNAL OF HAZARDOUS MATERIALS 2014; 265:1-7. [PMID: 24333709 DOI: 10.1016/j.jhazmat.2013.11.044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Revised: 11/05/2013] [Accepted: 11/20/2013] [Indexed: 06/03/2023]
Abstract
The potential bioavailability of phenanthrene aged in soil was determined by using a self-dying reporter bacterium, and the results were compared to two physicochemical measures, Tenax TA(®) bead-assisted desorption, and hydroxypropyl-β-cyclodextrin (HPCD) extraction. The reporter bacterium, capable of degrading phenanthrene as a sole carbon and energy source, was genetically reconstructed to die when it degrades phenanthrene. Therefore, population change of the reporter cells can be viewed as the quantification of bioavailable phenanthrene. When Ottawa sand was used as an aging matrix, the amounts of bioavailable phenanthrene (i.e. little gradual decrease) were similar, regardless of aging time, and consistent between the reporter bacterium and the two physicochemical measures. However, decrease in bioavailable phenanthrene with aging was readily evident in sandy loam with organic matter of 11.5%, with all three measures. More importantly, when the reporter bacterium was used, a rapid and significant decrease in the bioavailable fraction from 1.00 to 0.0431 was observed. The extent of decrease in bioavailable fraction was less than 40% in the two physicochemical measures, but was nearly 100% in the reporter bacterium, during the first 3 months of aging. Our results suggest that the phenanthrene fraction available to bacterial degradation, and probably the fraction that really manifests toxicity, may be much smaller than the fractions predicted with the physicochemical measures.
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Affiliation(s)
- Doyun Shin
- Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Gwahangno 124, Daejeon 305-350, Republic of Korea
| | - Kyoungphile Nam
- Department of Civil and Environmental Engineering, Seoul National University, Gwanakno 1, Seoul 151-744, Republic of Korea.
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12
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Johnson E, Srivastava R. Volatility in mRNA secondary structure as a design principle for antisense. Nucleic Acids Res 2013; 41:e43. [PMID: 23161691 PMCID: PMC3562002 DOI: 10.1093/nar/gks902] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2012] [Revised: 09/05/2012] [Accepted: 09/07/2012] [Indexed: 11/28/2022] Open
Abstract
Designing effective antisense sequences is a formidable problem. A method for predicting efficacious antisense holds the potential to provide fundamental insight into this biophysical process. More practically, such an understanding increases the chance of successful antisense design as well as saving considerable time, money and labor. The secondary structure of an mRNA molecule is believed to be in a constant state of flux, sampling several different suboptimal states. We hypothesized that particularly volatile regions might provide better accessibility for antisense targeting. A computational framework, GenAVERT was developed to evaluate this hypothesis. GenAVERT used UNAFold and RNAforester to generate and compare the predicted suboptimal structures of mRNA sequences. Subsequent analysis revealed regions that were particularly volatile in terms of intramolecular hydrogen bonding, and thus potentially superior antisense targets due to their high accessibility. Several mRNA sequences with known natural antisense target sites as well as artificial antisense target sites were evaluated. Upon comparison, antisense sequences predicted based upon the volatility hypothesis closely matched those of the naturally occurring antisense, as well as those artificial target sites that provided efficient down-regulation. These results suggest that this strategy may provide a powerful new approach to antisense design.
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Affiliation(s)
- Erik Johnson
- Department of Chemical, Materials and Biomolecular Engineering, University of
Connecticut, Storrs, CT 06269 and Program in Head and Neck Cancer and Oral
Oncology, Neag Comprehensive Cancer Center, University of Connecticut Health Center,
Farmington, CT 06030, USA
| | - Ranjan Srivastava
- Department of Chemical, Materials and Biomolecular Engineering, University of
Connecticut, Storrs, CT 06269 and Program in Head and Neck Cancer and Oral
Oncology, Neag Comprehensive Cancer Center, University of Connecticut Health Center,
Farmington, CT 06030, USA
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Moe-Behrens GHG, Davis R, Haynes KA. Preparing synthetic biology for the world. Front Microbiol 2013; 4:5. [PMID: 23355834 PMCID: PMC3554958 DOI: 10.3389/fmicb.2013.00005] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2012] [Accepted: 01/04/2013] [Indexed: 11/21/2022] Open
Abstract
Synthetic Biology promises low-cost, exponentially scalable products and global health solutions in the form of self-replicating organisms, or “living devices.” As these promises are realized, proof-of-concept systems will gradually migrate from tightly regulated laboratory or industrial environments into private spaces as, for instance, probiotic health products, food, and even do-it-yourself bioengineered systems. What additional steps, if any, should be taken before releasing engineered self-replicating organisms into a broader user space? In this review, we explain how studies of genetically modified organisms lay groundwork for the future landscape of biosafety. Early in the design process, biological engineers are anticipating potential hazards and developing innovative tools to mitigate risk. Here, we survey lessons learned, ongoing efforts to engineer intrinsic biocontainment, and how different stakeholders in synthetic biology can act to accomplish best practices for biosafety.
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Brinkman CL, Bumgarner R, Kittichotirat W, Dunman PM, Kuechenmeister LJ, Weaver KE. Characterization of the effects of an rpoC mutation that confers resistance to the Fst peptide toxin-antitoxin system toxin. J Bacteriol 2013; 195:156-66. [PMID: 23104812 PMCID: PMC3536179 DOI: 10.1128/jb.01597-12] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Accepted: 10/22/2012] [Indexed: 01/24/2023] Open
Abstract
Overexpression of the Fst toxin in Enterococcus faecalis strain OG1X leads to defects in chromosome segregation, cell division and, eventually, membrane integrity. The M7 mutant derivative of OG1X is resistant to most of these effects but shows a slight growth defect in the absence of Fst. Full-genome sequencing revealed two differences between M7 and its OG1X parent. First, OG1X contains a frameshift mutation that inactivates the etaR response regulator gene, while M7 is a wild-type revertant for etaR. Second, the M7 mutant contains a missense mutation in the rpoC gene, which encodes the β' subunit of RNA polymerase. Mutagenesis experiments revealed that the rpoC mutation was primarily responsible for the resistance phenotype. Microarray analysis revealed that a number of transporters were induced in OG1X when Fst was overexpressed. These transporters were not induced in M7 in response to Fst, and further experiments indicated that this had a direct protective effect on the mutant cells. Therefore, exposure of cells to Fst appears to have a cascading effect, first causing membrane stress and then potentiation of these effects by overexpression of certain transporters.
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Affiliation(s)
- Cassandra L. Brinkman
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, South Dakota, USA
| | - Roger Bumgarner
- Department of Microbiology, University of Washington, Seattle, Washington, USA
| | | | - Paul M. Dunman
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Lisa J. Kuechenmeister
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA
| | - Keith E. Weaver
- Division of Basic Biomedical Sciences, Sanford School of Medicine, University of South Dakota, Vermillion, South Dakota, USA
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Determination of phenanthrene bioavailability by using a self-dying reporter bacterium: Test with model solids and soil. J Biotechnol 2012; 157:454-9. [DOI: 10.1016/j.jbiotec.2011.07.041] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 06/27/2011] [Accepted: 07/25/2011] [Indexed: 11/21/2022]
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16
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Hayes F, Van Melderen L. Toxins-antitoxins: diversity, evolution and function. Crit Rev Biochem Mol Biol 2011; 46:386-408. [PMID: 21819231 DOI: 10.3109/10409238.2011.600437] [Citation(s) in RCA: 194] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Genes for toxin-antitoxin (TA) complexes are widespread in prokaryote genomes, and species frequently possess tens of plasmid and chromosomal TA loci. The complexes are categorized into three types based on genetic organization and mode of action. The toxins universally are proteins directed against specific intracellular targets, whereas the antitoxins are either proteins or small RNAs that neutralize the toxin or inhibit toxin synthesis. Within the three types of complex, there has been extensive evolutionary shuffling of toxin and antitoxin genes leading to considerable diversity in TA combinations. The intracellular targets of the protein toxins similarly are varied. Numerous toxins, many of which are sequence-specific endoribonucleases, dampen protein synthesis levels in response to a range of stress and nutritional stimuli. Key resources are conserved as a result ensuring the survival of individual cells and therefore the bacterial population. The toxin effects generally are transient and reversible permitting a set of dynamic, tunable responses that reflect environmental conditions. Moreover, by harboring multiple toxins that intercede in protein synthesis in response to different physiological cues, bacteria potentially sense an assortment of metabolic perturbations that are channeled through different TA complexes. Other toxins interfere with the action of topoisomersases, cell wall assembly, or cytoskeletal structures. TAs also play important roles in bacterial persistence, biofilm formation and multidrug tolerance, and have considerable potential both as new components of the genetic toolbox and as targets for novel antibacterial drugs.
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Affiliation(s)
- Finbarr Hayes
- Faculty of Life Sciences and Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester, UK.
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17
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Shin D, Moon HS, Lin CC, Barkay T, Nam K. Use of reporter-gene based bacteria to quantify phenanthrene biodegradation and toxicity in soil. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2011; 159:509-514. [PMID: 21093134 DOI: 10.1016/j.envpol.2010.10.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2010] [Revised: 10/07/2010] [Accepted: 10/10/2010] [Indexed: 05/30/2023]
Abstract
A phenanthrene-degrading bacterium, Sphingomonas paucimobilis EPA505 was used to construct two fluorescence-based reporter strains. Strain D harboring gfp gene was constructed to generate green fluorescence when the strain started to biodegrade phenanthrene. Strain S possessing gef gene was designed to die once phenanthrene biodegradation was initiated and thus to lose green fluorescence when visualized by a live/dead cell staining. Confocal laser scanning microscopic observation followed by image analysis demonstrates that the fluorescence intensity generated by strain D increased and the intensity by strain S decreased linearly at the phenanthrene concentration of up to 200 mg/L. Such quantitative increase and decrease of fluorescence intensity in strain D (i.e., from 1 to 11.90 ± 0.72) and strain S (from 1 to 0.40 ± 0.07) were also evident in the presence of Ottawa sand spiked with the phenanthrene up to 1000 mg/kg. The potential use of the reporter strains in quantitatively determining biodegradable or toxic phenanthrene was discussed.
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Affiliation(s)
- Doyun Shin
- Department of Civil and Environmental Engineering, Seoul National University, Gwanakno 599, Seoul 151-742, Republic of Korea
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18
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Westwater C, Kasman LM, Schofield DA, Werner PA, Dolan JW, Schmidt MG, Norris JS. Use of genetically engineered phage to deliver antimicrobial agents to bacteria: an alternative therapy for treatment of bacterial infections. Antimicrob Agents Chemother 2003; 47:1301-7. [PMID: 12654662 PMCID: PMC152521 DOI: 10.1128/aac.47.4.1301-1307.2003] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2002] [Revised: 11/04/2002] [Accepted: 12/27/2002] [Indexed: 11/20/2022] Open
Abstract
The emergence and increasing prevalence of multidrug-resistant bacterial pathogens emphasizes the need for new and innovative antimicrobial strategies. Lytic phages, which kill their host following amplification and release of progeny phage into the environment, may offer an alternative strategy for combating bacterial infections. In this study, however, we describe the use of a nonlytic phage to specifically target and deliver DNA encoding bactericidal proteins to bacteria. To test the concept of using phage as a lethal-agent delivery vehicle, we used the M13 phagemid system and the addiction toxins Gef and ChpBK. Phage delivery of lethal-agent phagemids reduced target bacterial numbers by several orders of magnitude in vitro and in a bacteremic mouse model of infection. Given the powerful genetic engineering tools available and the present knowledge in phage biology, this technology may have potential use in antimicrobial therapies and DNA vaccine development.
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Affiliation(s)
- Caroline Westwater
- Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, South Carolina 29403, USA.
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19
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Schofield DA, Westwater C, Dolan JW, Norris JS, Schmidt MG. Doc-mediated cell killing in Shigella flexneri using a C1/LacI controlled expression system. FEMS Microbiol Lett 2002; 215:237-42. [PMID: 12399040 DOI: 10.1111/j.1574-6968.2002.tb11396.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
In this report we describe the development of a highly stringent and dually regulated promoter system for Shigella flexneri. Dual regulation was provided by utilizing a promoter susceptible to control by the bacteriophage P1 temperature-sensitive C1 repressor that in turn was under the transcriptional control of LacI. The level of induction/repression ratios observed was up to 3700-fold in S. flexneri. The general utility of this promoter system was evaluated by demonstrating that the bacteriophage P1 post-segregational killer protein Doc mediates a bactericidal effect in S. flexneri. This represents the first report of Doc (death on curing)-mediated killing in this Gram-negative species.
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Affiliation(s)
- David A Schofield
- Department of Microbiology and Immunology, BSB 201, Medical University of South Carolina, 173 Ashley Avenue, Charleston 29403, USA.
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20
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Majerník A, Gottschalk G, Daniel R. Screening of environmental DNA libraries for the presence of genes conferring Na(+)(Li(+))/H(+) antiporter activity on Escherichia coli: characterization of the recovered genes and the corresponding gene products. J Bacteriol 2001; 183:6645-53. [PMID: 11673435 PMCID: PMC95496 DOI: 10.1128/jb.183.22.6645-6653.2001] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Environmental DNA libraries prepared from three different soils were screened for genes conferring Na(+)(Li(+))/H(+) antiporter activity on the antiporter-deficient Escherichia coli strain KNabc. The presence of those genes was verified on selective LK agar containing 7.5 mM LiCl. Two positive E. coli clones were obtained during the initial screening of 1,480,000 recombinant E. coli strains. Both clones harbored a plasmid (pAM1 and pAM3) that conferred a stable Li(+)-resistant phenotype. The insert of pAM2 (1,886 bp) derived from pAM1 contained a gene (1,185 bp) which encodes a novel Na(+)/H(+) antiporter belonging to the NhaA family. The insert of pAM3 harbored the DNA region of E. coli K-12 containing nhaA, nhaR, and gef. This region is flanked by highly conserved insertion elements. The sequence identity with E. coli decreased significantly outside of the insertion sequence elements, indicating that the unknown organism from which the insert of pAM3 was cloned is different from E. coli. The products of the antiporter genes located on pAM2 and pAM3 revealed functional homology to NhaA of E. coli and enabled the antiporter-deficient E. coli mutant to grow on solid media in the presence of up to 450 mM NaCl or 250 mM LiCl at pH 8.0. The Na(+)/H(+) antiporter activity in everted membrane vesicles that were derived from the E. coli strains KNabc/pAM2 and KNabc/pAM3 showed a substantial increase between pHs 7 and 8.5. The maximal activity was observed at pHs 8.3 and 8.6, respectively. The K(m) values of both antiporters for Na(+) were approximately 10-fold higher than the values for Li(+).
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Affiliation(s)
- A Majerník
- Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, 90028 Ivanka pri Dunaji, Slovak Republic
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21
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Cooper TF, Heinemann JA. Postsegregational killing does not increase plasmid stability but acts to mediate the exclusion of competing plasmids. Proc Natl Acad Sci U S A 2000; 97:12643-8. [PMID: 11058151 PMCID: PMC18817 DOI: 10.1073/pnas.220077897] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Postsegregational killing (PSK) systems consist of a tightly linked toxin-antitoxin pair. Antitoxin must be continually produced to prevent the longer lived toxin from killing the cell. PSK systems on plasmids are widely believed to benefit the plasmid by ensuring its stable vertical inheritance. However, experimental tests of this "stability" hypothesis were not consistent with its predictions. We suggest an alternative hypothesis to explain the evolution of PSK: that PSK systems have been selected through benefiting host plasmids in environments where plasmids must compete during horizontal reproduction. In this "competition" hypothesis, success of PSK systems is a consequence of plasmid-plasmid competition, rather than from an adaptive plasmid-host relationship. In support of this hypothesis, a plasmid-encoded parDE PSK system mediated the exclusion of an isogenic DeltaparDE plasmid. An understanding of how PSK systems influence plasmid success may provide insight into the evolution of other determinants (e.g., antibiotic resistance and virulence) also rendering a cell potentially dependent on an otherwise dispensable plasmid.
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Affiliation(s)
- T F Cooper
- Department of Plant and Microbial Sciences, Private Bag 4800, University of Canterbury, Christchurch, New Zealand
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22
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Abstract
The hok/sok locus of plasmid R1 mediates plasmid stabilization by the killing of plasmid-free cells. Many bacterial plasmids carry similar loci. For example, the F plasmid carries two hok homologues, flm and srnB, that mediate plasmid stabilization by this specialized type of programmed cell death. Here, we show that the chromosome of E. coli K-12 codes for five hok homologous loci, all of which specify Hok-like toxins. Three of the loci appear to be inactivated by the insertion elements IS150 or IS186 located close to but not in the toxin-encoding reading frames (i.e. hokA, hokC and hokE), one system is probably inactivated by point mutation (hokB), whereas the fifth system is inactivated by a major genetic rearrangement (hokD). In the ECOR collection of wild-type E. coli strains, we identified hokA and hokC loci without IS elements. A molecular and a genetic analysis show that the hokA and hokC loci specify unstable antisense RNAs and stable toxin-encoding mRNAs that are processed at their 3' ends. An alignment of the mRNA sequences reveals all the regulatory elements known to be required for correct folding and refolding of the plasmid-encoded mRNAs. The conserved elements include fbi that ensure a long-range interaction in the full-length mRNAs, and tac and antisense RNA target stem-loops that are required for translation and rapid antisense RNA binding of the processed mRNAs. Consistently, we find that the chromosome-encoded mRNAs are processed at their 3' ends, resulting in the presumed translationally active mRNAs. Despite the presence of all of the regulatory elements, the chromosome-encoded loci do not mediate plasmid stabilization by killing of plasmid-free cells. The chromosome-encoded mRNAs are poorly translated in vitro, thus yielding an explanation for the lacking phenotype. These observations suggest that the chromosomal hok-like genes may be induced by an as yet unknown signal.
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Affiliation(s)
- K Pedersen
- Department of Molecular Biology, Odense University, Campusvej 55, DK-5230 Odense M, Denmark
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23
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Plunkett G, Rose DJ, Durfee TJ, Blattner FR. Sequence of Shiga toxin 2 phage 933W from Escherichia coli O157:H7: Shiga toxin as a phage late-gene product. J Bacteriol 1999; 181:1767-78. [PMID: 10074068 PMCID: PMC93574 DOI: 10.1128/jb.181.6.1767-1778.1999] [Citation(s) in RCA: 305] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/1998] [Accepted: 01/06/1999] [Indexed: 11/20/2022] Open
Abstract
Lysogenic bacteriophages are major vehicles for the transfer of genetic information between bacteria, including pathogenicity and/or virulence determinants. In the enteric pathogen Escherichia coli O157:H7, which causes hemorrhagic colitis and hemolytic-uremic syndrome, Shiga toxins 1 and 2 (Stx1 and Stx2) are phage encoded. The sequence and analysis of the Stx2 phage 933W is presented here. We find evidence that the toxin genes are part of a late-phage transcript, suggesting that toxin production may be coupled with, if not dependent upon, phage release during lytic growth. Another phage gene, stk, encodes a product resembling eukaryotic serine/threonine protein kinases. Based on its position in the sequence, Stk may be produced by the prophage in the lysogenic state, and, like the YpkA protein of Yersinia species, it may interfere with the signal transduction pathway of the mammalian host. Three novel tRNA genes present in the phage genome may serve to increase the availability of rare tRNA species associated with efficient expression of pathogenicity determinants: both the Shiga toxin and serine/threonine kinase genes contain rare isoleucine and arginine codons. 933W also has homology to lom, encoding a member of a family of outer membrane proteins associated with virulence by conferring the ability to survive in macrophages, and bor, implicated in serum resistance.
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MESH Headings
- Attachment Sites, Microbiological/genetics
- Bacterial Toxins/genetics
- Base Sequence
- Coliphages/genetics
- Coliphages/ultrastructure
- DNA, Viral/genetics
- Escherichia coli O157/genetics
- Escherichia coli O157/pathogenicity
- Escherichia coli O157/virology
- Genes, Bacterial
- Genes, Viral
- Humans
- Microscopy, Electron
- Molecular Sequence Data
- Nucleic Acid Conformation
- Open Reading Frames
- Operator Regions, Genetic
- Promoter Regions, Genetic
- RNA, Transfer/chemistry
- RNA, Transfer/genetics
- RNA, Viral/chemistry
- RNA, Viral/genetics
- Shiga Toxins
- Terminator Regions, Genetic
- Virulence/genetics
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Affiliation(s)
- G Plunkett
- Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA
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24
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Abstract
This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.
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Affiliation(s)
- M K Berlyn
- Department of Biology and School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06520-8104, USA.
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25
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Bishop RE, Leskiw BK, Hodges RS, Kay CM, Weiner JH. The entericidin locus of Escherichia coli and its implications for programmed bacterial cell death. J Mol Biol 1998; 280:583-96. [PMID: 9677290 DOI: 10.1006/jmbi.1998.1894] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Antidote/toxin gene pairs known as "addiction modules" can maintain plasmids in bacterial populations by means of post-segregational killing. However, several chromosome-encoded addiction modules may provide an entirely distinct function in the programmed cell death of moribund subpopulations under starvation conditions. We now report a novel chromosomal bacteriolytic module of Escherichia coli called the entericidin locus, which is activated in stationary phase under high osmolarity conditions by sigmaS and simultaneously repressed by the osmoregulatory EnvZ/OmpR signal transduction pathway. The entericidin locus encodes tandem paralogous genes (ecnAB) and directs the synthesis of two small cell-envelope lipoproteins. An attenuator precedes ecnA and an ompR-sensitive sigmaS promoter governs expression of ecnB. The entericidin A lipoprotein is an antidote to the bacteriolytic lipoprotein entericidin B. The entericidins are predicted to adopt amphipathic alpha-helical structures and to reciprocally modulate membrane stability. The entericidin locus is not present on any known plasmids, but is conserved in the homologous region of the Citrobacter freundii chromosome. Although the cloned C. freundii entericidin locus is expressed in E. coli independently of ompR, it carries an additional ompR-like gene called ecnR. The organization of the entericidin locus as a chromosomal antidote/toxin gene pair, which is regulated by both positive and negative osmotic signals during starvation, is consistent with an emerging paradigm of programmed bacterial cell death.
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Affiliation(s)
- R E Bishop
- Department of Biochemistry and the MRC Group in the Molecular Biology of Membranes, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada
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26
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Mian IS, Moser MJ, Holley WR, Chatterjee A. Statistical modelling and phylogenetic analysis of a deaminase domain. J Comput Biol 1998; 5:57-72. [PMID: 9541871 DOI: 10.1089/cmb.1998.5.57] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Deamination reactions are catalyzed by a variety of enzymes including those involved in nucleoside/nucleotide metabolism and cytosine to uracil (C-->U) and adenosine to inosine (A-->I) mRNA editing. The active site of the deaminase (DM) domain in these enzymes contains a conserved histidine (or rarely cysteine), two cysteines and a glutamate proposed to act as a proton shuttle during deamination. Here, a statistical model, a hidden Markov model (HMM), of the DM domain has been created which identifies currently known DM domains and suggests new DM domains in viral, bacterial and eucaryotic proteins. However, no DM domains were identified in the currently predicted proteins from the archaeon Methanococcus jannaschii and possible causes for, and a potential means to ameliorate this situation are discussed. In some of the newly identified DM domains, the glutamate is changed to a residue that could not function as a proton shuttle and in one instance (Mus musculus spermatid protein TENR) the cysteines are also changed to lysine and serine. These may be non-competent DM domains able to bind but not act upon their substrate. Phylogenetic analysis using an HMM-generated alignment of DM domains reveals three branches with clear substructure in each branch. The results suggest DM domains that are candidates for yeast, platyhelminth, plant and mammalian C-->U and A-->I mRNA editing enzymes. Some bacterial and eucaryotic DM domains form distinct branches in the phylogenetic tree suggesting the existence of common, novel substrates.
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Affiliation(s)
- I S Mian
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA
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27
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Gerdes K, Gultyaev AP, Franch T, Pedersen K, Mikkelsen ND. Antisense RNA-regulated programmed cell death. Annu Rev Genet 1998; 31:1-31. [PMID: 9442888 DOI: 10.1146/annurev.genet.31.1.1] [Citation(s) in RCA: 171] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Eubacterial plasmids and chromosomes encode multiple killer genes belonging to the hok gene family. The plasmid-encoded killer genes mediate plasmid stabilization by killing plasmid-free cells. This review describes the genetics, molecular biology, and evolution of the hok gene family. The complicated antisense RNA-regulated control-loop that regulates posttranscriptional and postsegregational activation of killer mRNA translation in plasmid-free cells is described in detail. Nucleotide covariations in the mRNAs reveal metastable stem-loop structures that are formed at the mRNA 5' ends in the nascent transcripts. The metastable structures prevent translation and antisense RNA binding during transcription. Coupled nucleotide covariations provide evidence for a phylogenetically conserved mRNA folding pathway that involves sequential dynamic RNA rearrangements. Our analyses have elucidated an intricate mechanism by which translation of an antisense RNA-regulated mRNA can be conditionally activated. The complex phylogenetic relationships of the plasmid- and chromosome-encoded systems are also presented and discussed.
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Affiliation(s)
- K Gerdes
- Department of Molecular Biology, Odense University, Denmark.
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28
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Touati E. Participation of host gene functions in plasmid postsegregational killing: how and why. Res Microbiol 1997; 148:645-7. [PMID: 9765849 DOI: 10.1016/s0923-2508(99)80063-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- E Touati
- Unité de Programmation Moléculaire et de Toxicologie Génétique, CNRS URA 1444, Institut Pasteur, Paris
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29
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Holčík M, Iyer VM. Conditionally lethal genes associated with bacterial plasmids. MICROBIOLOGY (READING, ENGLAND) 1997; 143 ( Pt 11):3403-3416. [PMID: 9387219 DOI: 10.1099/00221287-143-11-3403] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Martin Holčík
- Department of Biology and Institute of Biochemistry, Carleton University, Ottawa Ontario Canada K1S5B6
| | - V M Iyer
- Department of Biology and Institute of Biochemistry, Carleton University, Ottawa Ontario Canada K1S5B6
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30
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Gultyaev AP, Franch T, Gerdes K. Programmed cell death by hok/sok of plasmid R1: coupled nucleotide covariations reveal a phylogenetically conserved folding pathway in the hok family of mRNAs. J Mol Biol 1997; 273:26-37. [PMID: 9367743 DOI: 10.1006/jmbi.1997.1295] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The hok/sok system of plasmid R1 mediates plasmid maintenance by killing of plasmid-free cells. Translation of the stable toxin-encoding hok mRNA is repressed by the unstable Sok antisense RNA. Using genetic algorithm simulations and phylogenetic comparisons, we analyse five plasmid-encoded and two chromosome-encoded hok-homologous mRNAs. A similar folding pathway was found for all mRNAs. Metastable hairpins at the very 5'-ends of the mRNAs were predicted to prevent the formation of structures required for translation and antisense RNA binding. Thus the folding of the mRNA 5'-ends appears to explain the apparent inactivity of the nascent transcripts. In the full-length mRNAs, long-range 5' to 3' interactions were predicted in all cases. The 5' to 3' interactions lock the mRNAs in inactive configurations. Translation of the mRNAs is activated by 3' exonucleolytic processing. Simulation of the 3' processing predicted that it triggers rearrangements of the mRNA 5'-ends with the formation of translational activator and antisense RNA target hairpins. Alignment of the mRNA sequences revealed a large number of nucleotide covariations that support the existence of the proposed secondary structures. Furthermore, coupled covariations support the folding pathway and provide evidence that the mRNA 5'-ends pair with three different partners during the proposed series of dynamic RNA rearrangements.
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Affiliation(s)
- A P Gultyaev
- Leiden Institute of Chemistry, Leiden University, The Netherlands
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31
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Gerdes K, Jacobsen JS, Franch T. Plasmid stabilization by post-segregational killing. GENETIC ENGINEERING 1997; 19:49-61. [PMID: 9193102 DOI: 10.1007/978-1-4615-5925-2_3] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- K Gerdes
- Department of Molecular Biology, Odense University, Denmark
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32
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Abstract
The hok (host killing) and sok (suppressor of killing) genes (hok/sok) efficiently maintain the low-copy-number plasmid R1. To investigate whether the hok/sok locus evolved as a phage-exclusion mechanism, Escherichia coli cells that contain hok/sok on a pBR322-based plasmid were challenged with T1, T4, T5, T7, and lambda phage. Upon infection with T4, the optical density of cells containing hok/sok on a high-copy-number plasmid continued to increase whereas the optical density for those lacking hok/sok rapidly declined. The presence of hok/sok reduced the efficiency of plating of T4 by 42% and decreased the plaque size by approximately 85%. Single-step growth experiments demonstrated that hok/sok decreased the T4 burst size by 40%, increased the time to form mature phage (eclipse time) from 22 to 30 min, and increased the time to cell lysis (latent period) from 30 to 60 min. These results further suggest that single cells exhibit altruistic behavior.
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Affiliation(s)
- D C Pecota
- Department of Chemical and Biochemical Engineering, University of California, Irvine, 92717-2575, USA
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33
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Tedin K, Witte A, Reisinger G, Lubitz W, Bläsi U. Evaluation of the E. coli ribosomal rrnB P1 promoter and phage-derived lysis genes for the use in a biological containment system: a concept study. J Biotechnol 1995; 39:137-48. [PMID: 7755968 DOI: 10.1016/0168-1656(95)00003-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A concept study devised for the development of a biological containment system has been conducted. We show that the lysis genes of different phage origin function in a variety of bacteria. They may therefore be suited for conditional suicide cassettes. Moreover, we tested whether the Escherichia coli rrnB P1 promoter could function as an environmentally responsive element sensing poor growth conditions expected after an accidental release of E. coli production strains from a bioreactor. Mimicking poor nutrient conditions by production of the alarmone guanosine tetraphosphate (ppGpp) with a plasmid encoded ppGpp synthetase I, the rrnB P1 promoter activity was completely turned off. These experiments suggested that the rrnB P1 promoter may be used as an efficient biosensor for altered growth conditions. A concept for a conditional suicide system employing the rrnB P1 promoter and phage-derived lysis genes as key components is discussed.
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Affiliation(s)
- K Tedin
- Institute of Microbiology and Genetics, Vienna Biocenter University of Vienna, Austria
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34
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Lehnherr H, Yarmolinsky MB. Addiction protein Phd of plasmid prophage P1 is a substrate of the ClpXP serine protease of Escherichia coli. Proc Natl Acad Sci U S A 1995; 92:3274-7. [PMID: 7724551 PMCID: PMC42148 DOI: 10.1073/pnas.92.8.3274] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Plasmid-encoded addiction genes augment the apparent stability of various low copy number bacterial plasmids by selectively killing plasmid-free (cured) segregants or their progeny. The addiction module of plasmid prophage P1 consists of a pair of genes called phd and doc. Phd serves to prevent host death when the prophage is retained and, should retention mechanisms fail, Doc causes death on curing. Doc acts as a cell toxin to which Phd is an antidote. In this study we show that host mutants with defects in either subunit of the ClpXP protease survive the loss of a plasmid that contains a P1 addiction module. The small antidote protein Phd is fully stable in these two mutant hosts, whereas it is labile in a wild-type host. We conclude that the role of ClpXP in the addiction mechanism of P1 is to degrade the Phd protein. This conclusion situates P1 among plasmids that elicit severe withdrawal symptoms and are able to do so because they encode both a cell toxin and an actively degraded macromolecule that blocks the synthesis or function of the toxin.
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Affiliation(s)
- H Lehnherr
- Laboratory of Biochemistry, National Cancer Institute, Bethesda, MD 20892-4255, USA
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35
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Klemm P, Jensen LB, Molin S. A stochastic killing system for biological containment of Escherichia coli. Appl Environ Microbiol 1995; 61:481-6. [PMID: 7574584 PMCID: PMC167306 DOI: 10.1128/aem.61.2.481-486.1995] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Bacteria with a stochastic conditional lethal containment system have been constructed. The invertible switch promoter located upstream of the fimA gene from Escherichia coli was inserted as expression cassette in front of the lethal gef gene deleted of its own natural promoter. The resulting fusion was placed on a plasmid and transformed to E. coli. The phenotype connected with the presence of such a plasmid was to reduce the population growth rate with increasing significance as the cell growth rate was reduced. In very fast growing cells, there was no measurable effect on growth rate. When a culture of E. coli harboring the plasmid comprising the containment system is left as stationary cells in suspension without nutrients, viability drops exponentially over a period of several days, in contrast to the control cells, which maintain viability nearly unaffected during the same period of time. Similar results were obtained with a strain in which the killing cassette was inserted in the chromosome. In competition with noncontained cells during growth, the contained cells are always outcompeted. Stochastic killing obtained by the fim-gef fusion is at present relevant only as a containment approach for E. coli, but the model may be mimicked in other organisms by using species-specific stochastic expression systems.
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Affiliation(s)
- P Klemm
- Department of Microbiology, Technical University of Denmark, Lyngby
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36
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Padan E, Schuldiner S. Molecular physiology of Na+/H+ antiporters, key transporters in circulation of Na+ and H+ in cells. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1185:129-51. [PMID: 8167133 DOI: 10.1016/0005-2728(94)90204-6] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- E Padan
- Department of Microbial and Molecular Ecology, Hebrew University of Jerusalem, Israel
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37
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Jensen LB, Ramos JL, Kaneva Z, Molin S. A substrate-dependent biological containment system for Pseudomonas putida based on the Escherichia coli gef gene. Appl Environ Microbiol 1993; 59:3713-7. [PMID: 8285679 PMCID: PMC182522 DOI: 10.1128/aem.59.11.3713-3717.1993] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
A model substrate-dependent suicide system to biologically contain Pseudomonas putida KT2440 is reported. The system consists of two elements. One element carries a fusion between a synthetic lac promoter (PA1-04/03) and the gef gene, which encodes a killing function. This element is contained within a transposaseless mini-Tn5 transposon so that it can be integrated at random locations on the Pseudomonas chromosome. The second element, harbored by plasmid pCC102, is designed to control the first and bears a fusion between the promoter of the P. putida TOL plasmid-encoded meta-cleavage pathway operon (Pm) and the lacI gene, encoding the Lac repressor, plus xylS2, coding for a positive regulator of Pm. In liquid culture under optimal growth conditions and in sterile and nonsterile soil microcosms, P. putida KT2440 (pWWO) bearing the containment system behaves as designed. In the presence of a XylS effector, such as m-methylbenzoate, the LacI protein is synthesized, preventing the expression of the killing function. In the absence of effectors, expression of the PA1-04/03::gef cassette is no longer prevented and a high rate of cell killing is observed. Fluctuation test analyses revealed that mutants resistant to cell killing arise at a frequency of around 10(-5) to 10(-6) per cell per generation. Mutations are linked to the killing element rather than to the regulatory one. In bacteria bearing two copies of the killing cassette, the rate of appearance of mutants resistant to killing decreased to as low as 10(-8) per cell per generation.
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Affiliation(s)
- L B Jensen
- Department of Microbiology, Technical University of Denmark, Lyngby
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38
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Bej AK, Molin S, Perlin M, Atlas RM. Maintenance and killing efficiency of conditional lethal constructs in Pseudomonas putida. ACTA ACUST UNITED AC 1992; 10:79-85. [PMID: 1368479 DOI: 10.1007/bf01583839] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Conditional lethal (suicidal) genetic constructs were designed and employed in strains of Pseudomonads as models for containment of genetically-engineered microbes that may be deliberately released into the environment. A strain of Pseudomonas putida was formed with a suicide vector designated pBAP24h that was constructed by cloning the host killing gene (hok) into the RSF1010 plasmid pVDtac24 and placing it under the control of the tac promoter. After hok induction in P. putida only 40% of surviving cells continued to bear the hok sequences within 4 h of induction; in contrast, 100% of the cells in uninduced controls bore hok. A few survivors that demonstrated resistance to hok-induced killing developed in P. putida, which may have been due to a mutation or physiological adaptation that rendered the membrane 'resistant' to hok. Conditional lethal strains of P. putida also were formed by inserting gef (a chromosomal homolog of hok) under the control of the tac promoter into the chromosome using a transposon. Constructs with chromosomal gef, as well as an RK2-derived plasmid construct containing gef, were only marginally more stable than the hok constructs; they were effective in killing P. putida when induced and within 2 h post-induction killing from either gef construct resulted in a 10(3)-10(5)-fold reduction in viable cell count compared to uninduced controls.
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Affiliation(s)
- A K Bej
- Department of Biology, University of Louisville, Kentucky 40292
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39
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SELBITSCHKA W, POHLER A, SIMON R. The construction of recA–deficient Rhizobium meliloti and R. leguminosarum strains marked with gusA or luc cassettes for use in risk–assessment studies. Mol Ecol 1992. [DOI: 10.1111/j.1365-294x.1992.tb00150.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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40
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Poulsen LK, Larsen NW, Molin S, Andersson P. Analysis of an Escherichia coli mutant strain resistant to the cell-killing function encoded by the gef gene family. Mol Microbiol 1992; 6:895-905. [PMID: 1602968 DOI: 10.1111/j.1365-2958.1992.tb01540.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The chromosomal genes gef and relF from Escherichia coli and the plasmid-encoded genes hok, flmA, srnB, and pndA constitute the gef gene family, which encodes a cell-killing function. In order to investigate the mechanism of cell killing we have isolated an E. coli mutant strain that is resistant to the overexpression of the toxic proteins encoded by the gef gene family. This phenotype requires at least two mutations, one of which has been mapped to 55.2 minutes. This mutation was sequenced and shown to represent a single base substitution in an open reading frame (ORF178) encoding a putative membrane protein having a molecular mass of 20.1 kDa. ORF178 and an upstream frame, ORF190, probably constitute an operon.
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Affiliation(s)
- L K Poulsen
- Biotechnological Institute, Technical University of Denmark, Lyngby
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41
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Amici A, Bazzicalupo M, Gallori E, Rollo F. Monitoring a genetically engineered bacterium in a freshwater environment by rapid enzymatic amplification of a synthetic DNA ?number-plate? Appl Microbiol Biotechnol 1991; 36:222-7. [PMID: 1369367 DOI: 10.1007/bf00164424] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In order to set up a sensitive and reliable detection method to monitor environmentally released genetically engineered microorganisms (GEMs) a 72-bp, double-stranded DNA fragment has been built by annealing and ligating four synthetic oligonucleotides. Binding sites for two 20-mer oligonucleotides are situated inside the DNA fragment, flanking the centre. Into the central part of the construction a 30-nucleotide identification sequence has been fitted. Thanks to the presence of the two oligonucleotide binding sites, the synthetic construction ("number-plate") can be submitted to enzymatic amplification using the polymerase chain reaction (PCR), thus enabling the identification system to take advantage of the outstanding sensitivity of this technique. When released into a freshwater microcosm, cells of Pseudomonas putida carrying a "number-plated" chromosome could be easily and rapidly detected merely by submitting boiled cell sediments to PCR amplification.
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Affiliation(s)
- A Amici
- Dipartimento di Biologia Molecolare Cellulare e Animale, Università di Camerino, Italy
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42
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Expression of a sodium proton antiporter (NhaA) in Escherichia coli is induced by Na+ and Li+ ions. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54700-1] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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43
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Nielsen AK, Thorsted P, Thisted T, Wagner EG, Gerdes K. The rifampicin-inducible genes srnB from F and pnd from R483 are regulated by antisense RNAs and mediate plasmid maintenance by killing of plasmid-free segregants. Mol Microbiol 1991; 5:1961-73. [PMID: 1722558 DOI: 10.1111/j.1365-2958.1991.tb00818.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The gene systems srnB of plasmid F and pnd of plasmid R483 were discovered because of their induction by rifampicin. Induction caused membrane damage, RNase I influx, degradation of stable RNA and, consequently, cell killing. We show here that the srnB and pnd systems mediate efficient stabilization of a mini-R1 test-plasmid. We also show that the killer genes srnB' and pndA are regulated by antisense RNAs, and that the srnC- and pndB-encoded antisense RNAs, denoted SrnC- and PndB-RNAs, are unstable molecules of approximately 60 nucleotides. The srnB and pndA mRNAs were found to be very stable. The differential decay rates of the inhibitory antisense RNAs and the killer-gene-encoding mRNAs explain the induction of these gene systems by rifampicin. Furthermore, the observed plasmid-stabilization phenotype associated with the srnB and pnd systems is a consequence of this differential RNA decay: the newborn plasmid-free cells inherit the stable mRNAs, which, after decay of the unstable antisense RNAs, are translated into killer proteins, thus leading to selective killing of the plasmid-free segregants. Thus our observations lead us to conclude that the F srnB and R483 pnd systems are phenotypically indistinguishable from the R1 hok/sok system, despite a 50% dissimilarity at the level of DNA sequence.
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Affiliation(s)
- A K Nielsen
- Department of Molecular Biology, Odense University, Denmark
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44
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Poulsen LK, Refn A, Molin S, Andersson P. Topographic analysis of the toxic Gef protein from Escherichia coli. Mol Microbiol 1991; 5:1627-37. [PMID: 1943700 DOI: 10.1111/j.1365-2958.1991.tb01910.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The chromosomal gef gene of Escherichia coli is a member of the gef gene family which encodes strongly toxic proteins of about 50 amino acids. We demonstrate here that the Gef protein is detectable by anti-peptide antibodies. Furthermore, we show that Gef is anchored in the cytoplasmic membrane by the N-terminal part of the protein, and that the C-terminal part is localized in the periplasm in a dimeric form with at least one disulphide bond. By mutagenesis of gef it is shown that the periplasmic portion of Gef encodes the toxic domain and that the dimerization of Gef is not essential for the toxic effect.
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Affiliation(s)
- L K Poulsen
- Genetic Engineering Group, Technical University of Denmark, Lyngby
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45
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Poulsen LK, Refn A, Molin S, Andersson P. The gef gene from Escherichia coli is regulated at the level of translation. Mol Microbiol 1991; 5:1639-48. [PMID: 1943701 DOI: 10.1111/j.1365-2958.1991.tb01911.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We describe post-transcriptional regulation of the chromosomal gene, gef, from Escherichia coli. The gef gene is a member of a gene family consisting of the chromosomal gef and relF genes from Escherichia coli and the hok, flmA, srnB, and pndA genes, which are situated on conjugative plasmids. All the genes encode small, toxic proteins of approximately 50 amino acids which are functionally and structurally homologous. Furthermore, the gene family shares post-transcriptional regulation of expression, albeit by different mechanisms. We demonstrate here that translation of gef is coupled to an upstream open reading frame which, in turn, is regulated by a transacting factor, probably an antisense RNA.
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Affiliation(s)
- L K Poulsen
- Genetic Engineering Group, Technical University of Denmark, Lyngby
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46
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Contreras A, Molin S, Ramos JL. Conditional-Suicide Containment System for Bacteria Which Mineralize Aromatics. Appl Environ Microbiol 1991; 57:1504-8. [PMID: 16348490 PMCID: PMC182976 DOI: 10.1128/aem.57.5.1504-1508.1991] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A model conditional-suicide system to control genetically engineered microorganisms able to degrade substituted benzoates is reported. The system is based on two elements. One element consists of a fusion between the promoter of the
Pseudomonas putida
TOL plasmid-encoded
meta
-cleavage pathway operon (P
m
) and the
lacI
gene encoding Lac repressor plus
xylS
, coding for the positive regulator of P
m
. The other element carries a fusion between the P
tac
promoter and the
gef
gene, which encodes a killing function. In the presence of XylS effectors, LacI protein is synthesized, preventing the expression of the killing function. In the absence of effectors, expression of the P
tac
::
gef
cassette is no longer prevented and a high rate of cell killing is observed. The substitution of XylS for XylSthr45, a mutant regulator with altered effector specificity and increased affinity for benzoates, allows the control of populations able to degrade a wider range of benzoates at micromolar substrate concentrations. Given the wide effector specificity of the key regulators, the wild-type and mutant XylS proteins, the system should allow the control of populations able to metabolize benzoate; methyl-, dimethyl-, chloro-, dichloro-, ethyl-, and methoxybenzoates; salicylate; and methyl- and chlorosalicylates. A small population of genetically engineered microorganisms became Gef resistant; however, the mechanism of such survival remains unknown.
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Affiliation(s)
- A Contreras
- Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Apto. 419, 18080 Granada, Spain, and Department of Microbiology, Technical University of Denmark, DK-2800 Lyngby, Denmark
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47
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Poulsen P, Jensen KF. Three genes preceding pyrE on the Escherichia coli chromosome are essential for survival and normal cell morphology in stationary culture and at high temperature. Res Microbiol 1991; 142:283-8. [PMID: 1925027 DOI: 10.1016/0923-2508(91)90042-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Previous studies of the upstream region of the pyrE gene in Escherichia coli revealed three genes of unknown function. Inactivation of these genes (designated orfE, orfX and orfY) by crossing the KmR-cassette-disrupted orf into the chromosome indicated that they were not required during exponential growth (Poulsen et al., Mol., Microbiol., 1989 b). Here we report that the three genes are of importance in the stationary phase. Thus, cultures of the mutants grown to a stationary state in rich media contained bacterial filaments of abnormal morphology. In addition, flow cytometric analyses showed that outgrown cultures of the orf mutants have anomalous size distribution and DNA content, and that rifampicin treatment of exponentially growing mutants results in cell populations with chromosome numbers in the range from about 1 to 10, compared with wild type strains that end up with 4 and 8 full chromosomes. Finally, it appeared that the three orf's are indispensable at high temperatures since the insertion mutants were unable to form colonies above 45 degrees C and since cultures of exponentially growing mutants lysed upon a temperature shift from 37 degrees C to 45 degrees C.
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Affiliation(s)
- P Poulsen
- University of Copenhagen, Institute of Biological Chemistry
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48
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Knudsen SM, Karlström OH. Development of efficient suicide mechanisms for biological containment of bacteria. Appl Environ Microbiol 1991; 57:85-92. [PMID: 2036024 PMCID: PMC182668 DOI: 10.1128/aem.57.1.85-92.1991] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
To optimize plasmid containment, we have systematically investigated the factors that limit the killing efficiency of a suicide system based on the relF gene from Escherichia coli controlled by inducible lac promoters and placed on plasmids. In induction experiments with this suicide system, killing efficiency was unaffected by temperature and growth medium; there was no requirement for great promoter strength or high plasmid copy number. We could demonstrate that the factors limiting killing were the mutation rate of the suicide function and the reduced growth rate caused by a basal level of expression of the suicide gene during normal growth, which can give a selective growth advantage to cells with mutated suicide functions. The capacity of the plasmid-carried killing system to contain the plasmid was tested in transformation, transduction, and conjugational mobilization. The rate of plasmid transfer detected in these experiments seemed too high to provide adequate biological containment. As expected from the induction experiments, plasmids that escaped containment in these transfer experiments turned out to be mutated in the suicide function. With lac-induced suicide as a test, the efficiency of the system was improved by tightening the repression of the suicide gene, thereby preventing selection of cells mutated in the killing function. Reduction of the mutational inactivation rate of the suicide system by duplication of the suicide function augmented the efficiency of the suicide dramatically. These results permit the construction of extremely efficient biological containment systems.
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Affiliation(s)
- S M Knudsen
- Institute of Microbiology, University of Copenhagen, Denmark
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49
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Gerdes K, Thisted T, Martinussen J. Mechanism of post-segregational killing by the hok/sok system of plasmid R1: sok antisense RNA regulates formation of a hok mRNA species correlated with killing of plasmid-free cells. Mol Microbiol 1990; 4:1807-18. [PMID: 1707122 DOI: 10.1111/j.1365-2958.1990.tb02029.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The hok/sok system of plasmid R1, which mediates plasmid stabilization via killing of plasmid-free segregants, encodes two genes: hok and sok. The hok gene product is a potent cell-killing protein. The expression of hok is regulated post-transcriptionally by the sok gene-encoded repressor, an antisense RNA complementary to the hok mRNA leader region. We show here that the hok mRNA is very stable, while the sok RNA decays rapidly. We also observe a new hok mRNA species which is 70 nucleotides shorter in the 3'-end than the full-length hok transcript. The appearance of the truncated hok mRNA was found to be regulated by the sok antisense RNA. Furthermore, the presence of the truncated hok mRNA was found to be correlated with efficient expression of the Hok protein. On the basis of these findings, we propose an extended model in order to explain the killing of plasmid-free segregants by the hok/sok system.
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Affiliation(s)
- K Gerdes
- Department of Molecular Biology, Odense University, Denmark
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