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Keshavam CC, Naz S, Gupta A, Sanyal P, Kochar M, Gangwal A, Sangwan N, Kumar N, Tyagi E, Goel S, Singh NK, Sowpati DT, Khare G, Ganguli M, Raze D, Locht C, Basu-Modak S, Gupta M, Nandicoori VK, Singh Y. The heparin-binding hemagglutinin protein of Mycobacterium tuberculosis is a nucleoid-associated protein. J Biol Chem 2023; 299:105364. [PMID: 37865319 PMCID: PMC10665949 DOI: 10.1016/j.jbc.2023.105364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 10/05/2023] [Accepted: 10/10/2023] [Indexed: 10/23/2023] Open
Abstract
Nucleoid-associated proteins (NAPs) regulate multiple cellular processes such as gene expression, virulence, and dormancy throughout bacterial species. NAPs help in the survival and adaptation of Mycobacterium tuberculosis (Mtb) within the host. Fourteen NAPs have been identified in Escherichia coli; however, only seven NAPs are documented in Mtb. Given its complex lifestyle, it is reasonable to assume that Mtb would encode for more NAPs. Using bioinformatics tools and biochemical experiments, we have identified the heparin-binding hemagglutinin (HbhA) protein of Mtb as a novel sequence-independent DNA-binding protein which has previously been characterized as an adhesion molecule required for extrapulmonary dissemination. Deleting the carboxy-terminal domain of HbhA resulted in a complete loss of its DNA-binding activity. Atomic force microscopy showed HbhA-mediated architectural modulations in the DNA, which may play a regulatory role in transcription and genome organization. Our results showed that HbhA colocalizes with the nucleoid region of Mtb. Transcriptomics analyses of a hbhA KO strain revealed that it regulates the expression of ∼36% of total and ∼29% of essential genes. Deletion of hbhA resulted in the upregulation of ∼73% of all differentially expressed genes, belonging to multiple pathways suggesting it to be a global repressor. The results show that HbhA is a nonessential NAP regulating gene expression globally and acting as a plausible transcriptional repressor.
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Affiliation(s)
| | - Saba Naz
- Department of Zoology, University of Delhi, Delhi, India; CSIR-Centre for Cellular and Molecular Biology, Hyderabad, India
| | - Aanchal Gupta
- CSIR-Institute of Genomics and Integrative Biology, New Delhi, India
| | - Priyadarshini Sanyal
- CSIR-Centre for Cellular and Molecular Biology, Hyderabad, India; Academy of Scientific and Innovative Research (AcSIR), CSIR- Centre for Cellular and Molecular Biology (CSIR-CCMB) Campus, Hyderabad, India
| | - Manisha Kochar
- Department of Zoology, University of Delhi, Delhi, India; CSIR-Institute of Genomics and Integrative Biology, New Delhi, India
| | | | - Nitika Sangwan
- Department of Zoology, University of Delhi, Delhi, India
| | - Nishant Kumar
- Department of Zoology, University of Delhi, Delhi, India
| | - Ekta Tyagi
- Department of Zoology, University of Delhi, Delhi, India
| | - Simran Goel
- Department of Zoology, University of Delhi, Delhi, India
| | | | | | - Garima Khare
- Department of Biochemistry, University of Delhi South Campus, New Delhi, India
| | - Munia Ganguli
- CSIR-Institute of Genomics and Integrative Biology, New Delhi, India
| | - Dominique Raze
- Univ. Lille, CNRS, Inserm, CHU Lille, Institut Pasteur de Lille, U1019 - UMR9017 - CIIL - Centre for Infection and Immunity of Lille, Lille, France
| | - Camille Locht
- Univ. Lille, CNRS, Inserm, CHU Lille, Institut Pasteur de Lille, U1019 - UMR9017 - CIIL - Centre for Infection and Immunity of Lille, Lille, France
| | | | - Meetu Gupta
- CSIR-Institute of Genomics and Integrative Biology, New Delhi, India.
| | - Vinay Kumar Nandicoori
- CSIR-Centre for Cellular and Molecular Biology, Hyderabad, India; Academy of Scientific and Innovative Research (AcSIR), CSIR- Centre for Cellular and Molecular Biology (CSIR-CCMB) Campus, Hyderabad, India; National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, India.
| | - Yogendra Singh
- Department of Zoology, University of Delhi, Delhi, India; Delhi School of Public Health, Institution of Eminence, University of Delhi, Delhi, India.
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Picker MA, Karney MMA, Gerson TM, Karabachev A, Duhart J, McKenna J, Wing H. Localized modulation of DNA supercoiling, triggered by the Shigella anti-silencer VirB, is sufficient to relieve H-NS-mediated silencing. Nucleic Acids Res 2023; 51:3679-3695. [PMID: 36794722 PMCID: PMC10164555 DOI: 10.1093/nar/gkad088] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Revised: 01/27/2023] [Accepted: 01/31/2023] [Indexed: 02/17/2023] Open
Abstract
In Bacteria, nucleoid structuring proteins govern nucleoid dynamics and regulate transcription. In Shigella spp., at ≤30°C, the histone-like nucleoid structuring protein (H-NS) transcriptionally silences many genes on the large virulence plasmid. Upon a switch to 37°C, VirB, a DNA binding protein and key transcriptional regulator of Shigella virulence, is produced. VirB functions to counter H-NS-mediated silencing in a process called transcriptional anti-silencing. Here, we show that VirB mediates a loss of negative DNA supercoils from our plasmid-borne, VirB-regulated PicsP-lacZ reporter in vivo. The changes are not caused by a VirB-dependent increase in transcription, nor do they require the presence of H-NS. Instead, the VirB-dependent change in DNA supercoiling requires the interaction of VirB with its DNA binding site, a critical first step in VirB-dependent gene regulation. Using two complementary approaches, we show that VirB:DNA interactions in vitro introduce positive supercoils in plasmid DNA. Subsequently, by exploiting transcription-coupled DNA supercoiling, we reveal that a localized loss of negative supercoils is sufficient to alleviate H-NS-mediated transcriptional silencing independently of VirB. Together, our findings provide novel insight into VirB, a central regulator of Shigella virulence and, more broadly, a molecular mechanism that offsets H-NS-dependent silencing of transcription in bacteria.
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Affiliation(s)
- Michael A Picker
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA
| | - Monika M A Karney
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA
| | - Taylor M Gerson
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA
| | | | - Juan C Duhart
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA
| | - Joy A McKenna
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA
| | - Helen J Wing
- School of Life Sciences, University of Nevada Las Vegas, Las Vegas, NV 89154-4004, USA
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3
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Picker MA, Karney MMA, Gerson TM, Karabachev AD, Duhart JC, McKenna JA, Wing HJ. Localized modulation of DNA supercoiling, triggered by the Shigella anti-silencer VirB, is sufficient to relieve H-NS-mediated silencing. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.09.523335. [PMID: 36711906 PMCID: PMC9882051 DOI: 10.1101/2023.01.09.523335] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In Bacteria, nucleoid structuring proteins govern nucleoid dynamics and regulate transcription. In Shigella spp ., at ≤ 30 °C, the histone-like nucleoid structuring protein (H-NS) transcriptionally silences many genes on the large virulence plasmid. Upon a switch to 37 °C, VirB, a DNA binding protein and key transcriptional regulator of Shigella virulence, is produced. VirB functions to counter H-NS-mediated silencing in a process called transcriptional anti-silencing. Here, we show that VirB mediates a loss of negative DNA supercoils from our plasmid-borne, VirB-regulated PicsP-lacZ reporter, in vivo . The changes are not caused by a VirB-dependent increase in transcription, nor do they require the presence of H-NS. Instead, the VirB-dependent change in DNA supercoiling requires the interaction of VirB with its DNA binding site, a critical first step in VirB-dependent gene regulation. Using two complementary approaches, we show that VirB:DNA interactions in vitro introduce positive supercoils in plasmid DNA. Subsequently, by exploiting transcription-coupled DNA supercoiling, we reveal that a localized loss of negative supercoils is sufficient to alleviate H-NS-mediated transcriptional silencing, independently of VirB. Together, our findings provide novel insight into VirB, a central regulator of Shigella virulence and more broadly, a molecular mechanism that offsets H-NS-dependent silencing of transcription in bacteria.
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Ageorges V, Monteiro R, Leroy S, Burgess CM, Pizza M, Chaucheyras-Durand F, Desvaux M. Molecular determinants of surface colonisation in diarrhoeagenic Escherichia coli (DEC): from bacterial adhesion to biofilm formation. FEMS Microbiol Rev 2021; 44:314-350. [PMID: 32239203 DOI: 10.1093/femsre/fuaa008] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 03/31/2020] [Indexed: 12/11/2022] Open
Abstract
Escherichia coli is primarily known as a commensal colonising the gastrointestinal tract of infants very early in life but some strains being responsible for diarrhoea, which can be especially severe in young children. Intestinal pathogenic E. coli include six pathotypes of diarrhoeagenic E. coli (DEC), namely, the (i) enterotoxigenic E. coli, (ii) enteroaggregative E. coli, (iii) enteropathogenic E. coli, (iv) enterohemorragic E. coli, (v) enteroinvasive E. coli and (vi) diffusely adherent E. coli. Prior to human infection, DEC can be found in natural environments, animal reservoirs, food processing environments and contaminated food matrices. From an ecophysiological point of view, DEC thus deal with very different biotopes and biocoenoses all along the food chain. In this context, this review focuses on the wide range of surface molecular determinants acting as surface colonisation factors (SCFs) in DEC. In the first instance, SCFs can be broadly discriminated into (i) extracellular polysaccharides, (ii) extracellular DNA and (iii) surface proteins. Surface proteins constitute the most diverse group of SCFs broadly discriminated into (i) monomeric SCFs, such as autotransporter (AT) adhesins, inverted ATs, heat-resistant agglutinins or some moonlighting proteins, (ii) oligomeric SCFs, namely, the trimeric ATs and (iii) supramolecular SCFs, including flagella and numerous pili, e.g. the injectisome, type 4 pili, curli chaperone-usher pili or conjugative pili. This review also details the gene regulatory network of these numerous SCFs at the various stages as it occurs from pre-transcriptional to post-translocational levels, which remains to be fully elucidated in many cases.
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Affiliation(s)
- Valentin Ageorges
- Université Clermont Auvergne, INRAE, MEDiS, F-63000 Clermont-Ferrand, France
| | - Ricardo Monteiro
- Université Clermont Auvergne, INRAE, MEDiS, F-63000 Clermont-Ferrand, France.,GSK, Via Fiorentina 1, 53100 Siena, Italy
| | - Sabine Leroy
- Université Clermont Auvergne, INRAE, MEDiS, F-63000 Clermont-Ferrand, France
| | - Catherine M Burgess
- Food Safety Department, Teagasc Food Research Centre, Ashtown, Dublin 15, Ireland
| | | | - Frédérique Chaucheyras-Durand
- Université Clermont Auvergne, INRAE, MEDiS, F-63000 Clermont-Ferrand, France.,Lallemand Animal Nutrition SAS, F-31702 Blagnac Cedex, France
| | - Mickaël Desvaux
- Université Clermont Auvergne, INRAE, MEDiS, F-63000 Clermont-Ferrand, France
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Piazza RM, Caetano BA, Henrique CP, Luz D, Munhoz DD, Polatto JM, Rocha LB, Silva MA, Mitsunari T. Immunological tests for diarrhoea caused by diarrhoeagenic Escherichia coli targeting their main virulence factors. J Microbiol Methods 2020. [DOI: 10.1016/bs.mim.2019.11.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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6
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NapA (Rv0430), a Novel Nucleoid-Associated Protein that Regulates a Virulence Operon in Mycobacterium tuberculosis in a Supercoiling-Dependent Manner. J Mol Biol 2019; 431:1576-1591. [DOI: 10.1016/j.jmb.2019.02.029] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2018] [Revised: 02/23/2019] [Accepted: 02/25/2019] [Indexed: 12/17/2022]
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7
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Ahmed W, Menon S, Karthik PV, Nagaraja V. Reduction in DNA topoisomerase I level affects growth, phenotype and nucleoid architecture of Mycobacterium smegmatis. MICROBIOLOGY-SGM 2014; 161:341-353. [PMID: 25516959 DOI: 10.1099/mic.0.000014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The steady-state negative supercoiling of eubacterial genomes is maintained by the action of DNA topoisomerases. Topoisomerase distribution varies in different species of mycobacteria. While Mycobacterium tuberculosis (Mtb) contains a single type I (TopoI) and a single type II (Gyrase) enzyme, Mycobacterium smegmatis (Msm) and other members harbour additional relaxases. TopoI is essential for Mtb survival. However, the necessity of TopoI or other relaxases in Msm has not been investigated. To recognize the importance of TopoI for growth, physiology and gene expression of Msm, we have developed a conditional knock-down strain of TopoI in Msm. The TopoI-depleted strain exhibited extremely slow growth and drastic changes in phenotypic characteristics. The cessation of growth indicates the essential requirement of the enzyme for the organism in spite of having additional DNA relaxation enzymes in the cell. Notably, the imbalance in TopoI level led to the altered expression of topology modulatory proteins, resulting in a diffused nucleoid architecture. Proteomic and transcript analysis of the mutant indicated reduced expression of the genes involved in central metabolic pathways and core DNA transaction processes. RNA polymerase (RNAP) distribution on the transcription units was affected in the TopoI-depleted cells, suggesting global alteration in transcription. The study thus highlights the essential requirement of TopoI in the maintenance of cellular phenotype, growth characteristics and gene expression in mycobacteria. A decrease in TopoI level led to altered RNAP occupancy and impaired transcription elongation, causing severe downstream effects.
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Affiliation(s)
- Wareed Ahmed
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Shruti Menon
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Pullela V Karthik
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
| | - Valakunja Nagaraja
- Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India.,Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
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8
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Rocha LB, Santos ARR, Munhoz DD, Cardoso LTA, Luz DE, Andrade FB, Horton DSPQ, Elias WP, Piazza RMF. Development of a rapid agglutination latex test for diagnosis of enteropathogenic and enterohemorrhagic Escherichia coli infection in developing world: defining the biomarker, antibody and method. PLoS Negl Trop Dis 2014; 8:e3150. [PMID: 25254981 PMCID: PMC4177769 DOI: 10.1371/journal.pntd.0003150] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Accepted: 07/29/2014] [Indexed: 12/16/2022] Open
Abstract
Background Enteropathogenic and enterohemorrhagic Escherichia coli (EPEC/EHEC) are human intestinal pathogens responsible for diarrhea in both developing and industrialized countries. In research laboratories, EPEC and EHEC are defined on the basis of their pathogenic features; nevertheless, their identification in routine laboratories is expensive and laborious. Therefore, the aim of the present work was to develop a rapid and simple assay for EPEC/EHEC detection. Accordingly, the EPEC/EHEC-secreted proteins EspA and EspB were chosen as target antigens. Methodology First, we investigated the ideal conditions for EspA/EspB production/secretion by ELISA in a collection of EPEC/EHEC strains after cultivating bacterial isolates in Dulbecco’s modified Eagle’s medium (DMEM) or DMEM containing 1% tryptone or HEp-2 cells-preconditioned DMEM, employing either anti-EspA/anti-EspB polyclonal or monoclonal antibodies developed and characterized herein. Subsequently, a rapid agglutination latex test (RALT) was developed and tested with the same collection of bacterial isolates. Principal findings EspB was defined as a biomarker and its corresponding monoclonal antibody as the tool for EPEC/EHEC diagnosis; the production of EspB was better in DMEM medium. RALT assay has the sensitivity and specificity required for high-impact diagnosis of neglected diseases in the developing world. Conclusion RALT assay described herein can be considered an alternative assay for diarrhea diagnosis in low-income countries since it achieved 97% sensitivity, 98% specificity and 97% efficiency. A rapid and low-cost diagnosis for EPEC/EHEC infections is extremely required considering their global prevalence, the severity of the diseases associated with them, and the fact that the use of antibiotics to treat EHEC infections can be harmful. For EHEC, the detection of Stx toxins has already been developed, but for EPEC, an internationally recognized standard diagnostic test is lacking. Thus, the approach for their rapid detection in this study was the use of the secreted proteins EspA and/or EspB, since they are the major secreted proteins in both pathogens. EspB was defined as a biomarker and its corresponding monoclonal antibody as the tool for EPEC/EHEC diagnosis using a latex agglutination assay, which can be employed in less equipped laboratories in developing countries.
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Affiliation(s)
- Letícia B. Rocha
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
| | - Anna R. R. Santos
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
| | - Danielle D. Munhoz
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
| | - Lucas T. A. Cardoso
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
| | - Daniela E. Luz
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
| | - Fernanda B. Andrade
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
| | | | - Waldir P. Elias
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
| | - Roxane M. F. Piazza
- Laboratório de Bacteriologia, Instituto Butantan, São Paulo, São Paulo, Brazil
- * E-mail:
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Steinmann R, Dersch P. Thermosensing to adjust bacterial virulence in a fluctuating environment. Future Microbiol 2013; 8:85-105. [PMID: 23252495 DOI: 10.2217/fmb.12.129] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The lifecycle of most microbial pathogens can be divided into two states: existence outside and inside their hosts. The sudden temperature upshift experienced upon entry from environmental or vector reservoirs into a warm-blooded host is one of the most crucial signals informing the pathogens to adjust virulence gene expression and their host-stress survival program. This article reviews the plethora of sophisticated strategies that bacteria have evolved to sense temperature, and outlines the molecular signal transduction mechanisms used to modulate synthesis of crucial virulence determinants. The molecular details of thermal control through conformational changes of DNA, RNA and proteins are summarized, complex and diverse thermosensing principles are introduced and their potential as drug targets or synthetic tools are discussed.
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Affiliation(s)
- Rebekka Steinmann
- Department of Molecular Infection Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany
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10
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Shapiro RS, Cowen LE. Thermal control of microbial development and virulence: molecular mechanisms of microbial temperature sensing. mBio 2012; 3:e00238-12. [PMID: 23033469 PMCID: PMC3518907 DOI: 10.1128/mbio.00238-12] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Temperature is a critical and ubiquitous environmental signal that governs the development and virulence of diverse microbial species, including viruses, archaea, bacteria, fungi, and parasites. Microbial survival is contingent upon initiating appropriate responses to the cellular stress induced by severe environmental temperature change. In the case of microbial pathogens, development and virulence are often coupled to sensing host physiological temperatures. As such, microbes have developed diverse molecular strategies to sense fluctuations in temperature, and nearly all cellular molecules, including proteins, lipids, RNA, and DNA, can act as thermosensors that detect changes in environmental temperature and initiate relevant cellular responses. The myriad of molecular mechanisms by which microbes sense and respond to temperature reveals an elegant repertoire of strategies to orchestrate cellular signaling, developmental programs, and virulence with spatial and temporal environmental cues.
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Affiliation(s)
- Rebecca S Shapiro
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
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11
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Wong-Beringer A, Wiener-Kronish J, Lynch S, Flanagan J. Comparison of type III secretion system virulence among fluoroquinolone-susceptible and -resistant clinical isolates of Pseudomonas aeruginosa. Clin Microbiol Infect 2008; 14:330-6. [DOI: 10.1111/j.1469-0691.2007.01939.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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12
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Franzon JH, Santos DS. A role for histone-like protein H1 (H-NS) in the regulation of hemolysin expression by Serratia marcescens. Braz J Med Biol Res 2004; 37:1763-9. [PMID: 15558182 DOI: 10.1590/s0100-879x2004001200001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The histone-like protein H1 (H-NS) is an abundant structural component of the bacterial nucleoid and influences many cellular processes including recombination, transcription and transposition. Mutations in the hns gene encoding H-NS are highly pleiotropic, affecting the expression of many unrelated genes. We have studied the role of H-NS on the regulation of hemolysin gene expression in Serratia marcescens. The Escherichia coli hns mutant carrying S. marcescens hemolysin genes on a plasmid constructed by ligation of the 3.2-kb HindIII-SacI fragment of pR02 into pBluescriptIIKS, showed a high level of expression of this hemolytic factor. To determine the osmoregulation of wild-type and hns defective mutants the cells were grown to mid-logarithmic phase in LB medium with 0.06 or 0.3 M NaCl containing ampicillin and kanamycin, whereas to analyze the effect of pH on hemolysin expression, the cells were grown to late-logarithmic phase in LB medium buffered with 0.1 M Tris-HCl, pH 4.5 to 8.0. To assay growth phase-related hemolysin production, bacterial cells were grown in LB medium supplemented with ampicillin and kanamycin. The expression of S. marcescens hemolysin genes in wild-type E. coli and in an hns-defective derivative at different pH and during different growth phases indicated that, in the absence of H-NS, the expression of hemolysin did not vary with pH changes or growth phases. Furthermore, the data suggest that H-NS may play an important role in the regulation of hemolysin expression in S. marcescens and its effect may be due to changes in DNA topology influencing transcription and thus the amount of hemolysin expression. Implications for the mechanism by which H-NS influences gene expression are discussed.
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Affiliation(s)
- J H Franzon
- Programa de Pós-Graduação em Genética e Biologia Molecular, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
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13
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Wing HJ, Yan AW, Goldman SR, Goldberg MB. Regulation of IcsP, the outer membrane protease of the Shigella actin tail assembly protein IcsA, by virulence plasmid regulators VirF and VirB. J Bacteriol 2004; 186:699-705. [PMID: 14729695 PMCID: PMC321486 DOI: 10.1128/jb.186.3.699-705.2004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The Shigella outer membrane protease IcsP removes the actin assembly protein IcsA from the bacterial surface, and consequently modulates Shigella actin-based motility and cell-to-cell spread. Here, we demonstrate that IcsP expression is undetectable in mutants lacking either of two transcriptional activators, VirF and VirB. In wild-type Shigella spp., virB expression is entirely dependent on VirF; therefore, to circumvent this regulatory cascade, we independently expressed VirF or VirB in Shigella strains lacking both activators and measured both IcsP levels and transcription from the icsP promoter. Our results show that VirB significantly enhanced icsP transcription, even in the absence of VirF. In contrast, when VirF was induced in the absence of VirB, VirF had variable effects. The regulation of icsP is distinctly different from the regulation of the gene encoding its major substrate, icsA, which is activated by VirF and not VirB. We propose that the different pathways regulating icsA and icsP may be critical to the modulation of IcsA-mediated actin-based motility by IcsP.
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Affiliation(s)
- Helen J Wing
- Infectious Disease Division, Massachusetts General Hospital, Cambridge, Massachusetts 02139, USA
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14
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Hraiky C, Raymond MA, Drolet M. RNase H overproduction corrects a defect at the level of transcription elongation during rRNA synthesis in the absence of DNA topoisomerase I in Escherichia coli. J Biol Chem 2000; 275:11257-63. [PMID: 10753935 DOI: 10.1074/jbc.275.15.11257] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It has been suggested that the major function of DNA topoisomerase I in Escherichia coli is to suppress the formation of R-loops, which could inhibit growth. Although the currently available data suggest that the inhibitory effect of R-loops is exerted at the level of gene expression, this has never been demonstrated. In the present report, we show that rRNA synthesis is significantly impaired at the level of transcription elongation in a bacterial strain lacking DNA topoisomerase I. We found that this inhibition is due to transcriptional blocks. RNase H overproduction is also shown to considerably reduce the extent of such transcriptional blocks during rRNA synthesis. Moreover, one of these transcriptional blockage sites is located within a region where extensive R-loop formation was previously shown to occur on a plasmid DNA in the absence of DNA topoisomerase I. Together, these results allow us to propose that an important function of DNA topoisomerase I is to inhibit the formation of R-loops, which may otherwise translate into roadblocks for RNA polymerases. Our results also highlight the potential regulatory role of DNA supercoiling at the level of transcription elongation.
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Affiliation(s)
- C Hraiky
- Département de Microbiologie et Immunologie, Université de Montréal, Québec H3C 3J7, Canada
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15
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Cornelis GR, Boland A, Boyd AP, Geuijen C, Iriarte M, Neyt C, Sory MP, Stainier I. The virulence plasmid of Yersinia, an antihost genome. Microbiol Mol Biol Rev 1998; 62:1315-52. [PMID: 9841674 PMCID: PMC98948 DOI: 10.1128/mmbr.62.4.1315-1352.1998] [Citation(s) in RCA: 599] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The 70-kb virulence plasmid enables Yersinia spp. (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) to survive and multiply in the lymphoid tissues of their host. It encodes the Yop virulon, an integrated system allowing extracellular bacteria to disarm the cells involved in the immune response, to disrupt their communications, or even to induce their apoptosis by the injection of bacterial effector proteins. This system consists of the Yop proteins and their dedicated type III secretion apparatus, called Ysc. The Ysc apparatus is composed of some 25 proteins including a secretin. Most of the Yops fall into two groups. Some of them are the intracellular effectors (YopE, YopH, YpkA/YopO, YopP/YopJ, YopM, and YopT), while the others (YopB, YopD, and LcrV) form the translocation apparatus that is deployed at the bacterial surface to deliver the effectors into the eukaryotic cells, across their plasma membrane. Yop secretion is triggered by contact with eukaryotic cells and controlled by proteins of the virulon including YopN, TyeA, and LcrG, which are thought to form a plug complex closing the bacterial secretion channel. The proper operation of the system also requires small individual chaperones, called the Syc proteins, in the bacterial cytosol. Transcription of the genes is controlled both by temperature and by the activity of the secretion apparatus. The virulence plasmid of Y. enterocolitica and Y. pseudotuberculosis also encodes the adhesin YadA. The virulence plasmid contains some evolutionary remnants including, in Y. enterocolitica, an operon encoding resistance to arsenic compounds.
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Affiliation(s)
- G R Cornelis
- Microbial Pathogenesis Unit, Christian de Duve Institute of Cellular Pathology and Faculté de Médecine, Université Catholique de Louvain, B-1200 Brussels, Belgium.
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16
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Falconi M, Colonna B, Prosseda G, Micheli G, Gualerzi CO. Thermoregulation of Shigella and Escherichia coli EIEC pathogenicity. A temperature-dependent structural transition of DNA modulates accessibility of virF promoter to transcriptional repressor H-NS. EMBO J 1998; 17:7033-43. [PMID: 9843508 PMCID: PMC1171051 DOI: 10.1093/emboj/17.23.7033] [Citation(s) in RCA: 223] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The expression of plasmid-borne virF of Shigella encoding a transcriptional regulator of the AraC family, is required to initiate a cascade of events resulting in activation of several operons encoding invasion functions. H-NS, one of the main nucleoid-associated proteins, controls the temperature-dependent expression of the virulence genes by repressing the in vivo transcription of virF only below a critical temperature (approximately 32 degrees C). This temperature-dependent transcriptional regulation has been reproduced in vitro and the targets of H-NS on the virF promoter were identified as two sites centred around -250 and -1 separated by an intrinsic DNA curvature. H-NS bound cooperatively to these two sites below 32 degrees C, but not at 37 degrees C. DNA supercoiling within the virF promoter region did not influence H-NS binding but was necessary for the H-NS-mediated transcriptional repression. Electrophoretic analysis between 4 and 60 degrees C showed that the virF promoter fragment, comprising the two H-NS sites, undergoes a specific and temperature-dependent conformational transition at approximately 32 degrees C. Our results suggest that this modification of the DNA target may modulate a cooperative interaction between H-NS molecules bound at two distant sites in the virF promoter region and thus represents the physical basis for the H-NS-dependent thermoregulation of virulence gene expression.
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Affiliation(s)
- M Falconi
- Laboratorio di Genetica, Dipartimento di Biologia MCA, Università di Camerino, 62032 Camerino (MC), Italy
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17
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Bhaduri T, Bagui TK, Sikder D, Nagaraja V. DNA topoisomerase I from Mycobacterium smegmatis. An enzyme with distinct features. J Biol Chem 1998; 273:13925-32. [PMID: 9593741 DOI: 10.1074/jbc.273.22.13925] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A type I topoisomerase has been purified to homogeneity from Mycobacterium smegmatis. It is the largest single subunit enzyme of this class having molecular mass of 110 kDa. The enzyme is Mg2+ dependent and can relax negatively supercoiled DNA, catenate, and knot single-stranded DNA, thus having typical properties of type I topoisomerases. Furthermore, the enzyme makes single-stranded nicks and the 5'-phosphoryl end of the nicked DNA gets covalently linked with a tyrosine residue of the enzyme. However, M. smegmatis enzyme shows some distinctive features from the prototype Escherichia coli topoisomerase I. The enzyme is relatively stable at higher temperatures and not inhibited by spermidine. It apparently does not contain any bound Zn2+ and on modification of cysteine residues retains the activity, suggesting the absence of the zinc-finger motif in DNA binding. Partially purified Mycobacterium tuberculosis topoisomerase I exhibits very similar properties with respect to size, stability, and reaction characteristics. Sequence comparison of topoisomerase I from E. coli and M. tuberculosis shows the absence of zinc-finger motifs in mycobacterial enzyme. Using a two-substrate assay system, we demonstrate that the enzyme acts processively at low ionic strength and switches over to distributive mode at high Mg2+ concentration. Significantly, the enzyme activity is stimulated by single strand DNA-binding protein. There is a potential to exploit the characteristics of the enzyme to develop it as a molecular target against mycobacterial infections.
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Affiliation(s)
- T Bhaduri
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
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18
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Suerbaum S, Brauer-Steppkes T, Labigne A, Cameron B, Drlica K. Topoisomerase I of Helicobacter pylori: juxtaposition with a flagellin gene (flaB) and functional requirement of a fourth zinc finger motif. Gene 1998; 210:151-61. [PMID: 9524255 DOI: 10.1016/s0378-1119(98)00065-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Cloning and nucleotide sequence analysis showed that in Helicobacter pylori the gene encoding topoisomerase I (topA) lies about 170 nucleotides upstream from flaB, a gene encoding one of the two flagellin proteins that is required for virulence. The topA and flaB genes are divergently transcribed. The orientation and spatial relationship between flaB and topA are remarkably conserved among strains of a bacterium in which genomic rearrangements are common. The deduced amino acid sequence of topoisomerase I revealed four zinc finger motifs, one more than has been reported previously for the Escherichia coli homologue. The additional motif, which is near the C-terminus of the protein, appears to be essential for function since mutations in that region are lethal. These data show that TopA proteins can be divided into several classes on the basis of zinc finger motifs and raise the interesting possibility that the H. pylori enzyme has local topological effects focussed on a flagellin gene.
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Affiliation(s)
- S Suerbaum
- Ruhr-Universität Bochum, Medizinische Mikrobiologie und Immunologie, Bochum, Germany.
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19
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Prosseda G, Fradiani PA, Di Lorenzo M, Falconi M, Micheli G, Casalino M, Nicoletti M, Colonna B. A role for H-NS in the regulation of the virF gene of Shigella and enteroinvasive Escherichia coli. Res Microbiol 1998; 149:15-25. [PMID: 9766205 DOI: 10.1016/s0923-2508(97)83619-4] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We have investigated the role of H-NS, one of the major components of the bacterial nucleoid, in the expression of the virF gene present on the large virulence plasmid of Shigella and enteroinvasive Escherichia coli in response to different environmental conditions. VirF is an AraC-like protein which activates at least two promoters, virB and virG, both repressed by H-NS. Band shift experiments reveal that the affinity of H-NS for the virF and virB promoters is comparable, while the affinity for the virG promoter is higher. Polyacrylamide gel electrophoresis of three DNA fragments containing the virF, the virB and the VirG promoters demonstrates, in agreement with computer predictions, that they have an intrinsically curved structure, confirming the preference of H-NS for bent DNA. In vivo transcriptional analysis of virF mRNA shows that H-NS negatively controls the expression of virF at 30 degrees C. The expression of a virF-lacZ translational fusion in E.coli wild type and in an hns-defective derivative grown at 30 degrees or 37 degrees C and at pH 6.0 or 7.0 indicates that, in the absence of H-NS, virF expression becomes insensitive to temperature and to limited pH changes. Our results strongly suggest that H-NS controls virF expression by binding to the virF promoter and by repressing its expression at low temperature and at low pH.
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Affiliation(s)
- G Prosseda
- Dip.Biologia Cellulare e dello Sviluppo, Università La Sapienza, Rome, Italy
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20
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Hay NA, Tipper DJ, Gygi D, Hughes C. A nonswarming mutant of Proteus mirabilis lacks the Lrp global transcriptional regulator. J Bacteriol 1997; 179:4741-6. [PMID: 9244260 PMCID: PMC179319 DOI: 10.1128/jb.179.15.4741-4746.1997] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Proteus swarming is the rapid cyclical population migration across surfaces by elongated cells that hyperexpress flagellar and virulence genes. The mini-Tn5 transposon mutant mns2 was isolated as a tight nonswarming mutant that did not elongate or upregulate flagellar and hemolysin genes. Individual cell motility was retained but was reduced. The transposon had inserted in the gene encoding the global transcriptional regulator Lrp (leucine-responsive regulatory protein), expression of which was upregulated in differentiating swarm cells. Swarming was restored to the lrp mutant by artificial overexpression of the flhDC flagellar regulatory master operon. Lrp may be a key component in generating or relaying signals that are required for flagellation and swarming, possibly acting through the flhDC operon.
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Affiliation(s)
- N A Hay
- Department of Pathology, University of Cambridge, United Kingdom
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21
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Vanmaele RP, Armstrong GD. Effect of carbon source on localized adherence of enteropathogenic Escherichia coli. Infect Immun 1997; 65:1408-13. [PMID: 9119481 PMCID: PMC175147 DOI: 10.1128/iai.65.4.1408-1413.1997] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Enteropathogenic Escherichia coli (EPEC) strains attach to epithelial cells as discrete clusters of bacteria which are localized at a few sites on the cell surface. Previously, it was shown that this localized-adherence (LA) phenotype is induced by specific growth conditions. We found that wild-type EPEC attached to HEp-2 cells in an LA pattern when the bacteria were grown in Dulbecco's modified Eagle medium (DMEM) containing glucose as the carbon source. In contrast, bacteria incubated in DMEM containing galactose did not adhere to epithelial cells. The latter results were similar to those observed when JPN15, an LA-negative strain, was grown under conditions which promoted bacterial binding. The differences in attachment of wild-type EPEC were independent of the stage of log-phase growth of the cultures and of the number of CFU incubated with the HEp-2 monolayers. Expression of the adherence phenotype by organisms grown in glucose was associated with increased expression of intimin and bundle-forming pilin. In contrast, bacteria grown in medium containing galactose expressed these proteins at levels similar to those observed when JPN15 was grown in medium containing glucose.
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Affiliation(s)
- R P Vanmaele
- Medical Microbiology and Immunology, University of Alberta, Edmonton, Canada
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22
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Rosenshine I, Ruschkowski S, Finlay BB. Expression of attaching/effacing activity by enteropathogenic Escherichia coli depends on growth phase, temperature, and protein synthesis upon contact with epithelial cells. Infect Immun 1996; 64:966-73. [PMID: 8641808 PMCID: PMC173864 DOI: 10.1128/iai.64.3.966-973.1996] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Enteropathogenic Escherichia coli (EPEC) induces tyrosine phosphorylation of a 90-kDa protein (Hp90) in infected epithelial cells. This in turn facilitates intimate binding of EPEC via the outer membrane protein intimin, effacement of host cell microvilli, cytoskeletal rearrangement, and bacterial uptake. This phenotype has been commonly referred to as attaching/effacing (A/E). The ability of EPEC to induce A/E lesions was dependent on bacterial growth phase and temperature. Early-logarithmic-phase EPEC grown at 37 degrees C elicits strong A/E activity within minutes after infection of HeLa epithelial cells. EPEC de novo protein syntheses during the first minutes of interaction with the host cell was required to elicit A/E lesions. However, once formed, bacterial viability was not needed to maintain A/E lesions. The type of growth media and partial O2 pressure level do not seem to affect the ability of EPEC to cause A/E lesions. These results indicates that the A/E activity of EPEC is tightly regulated by environmental and host factors.
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Affiliation(s)
- I Rosenshine
- Department of Biotechnology and Molecular Genetics, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
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23
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Contreras I, Muñoz L, Toro CS, Mora GC. Heterologous expression of Escherichia coli porin genes in Salmonella typhi Ty2: regulation by medium osmolarity, temperature and oxygen availability. FEMS Microbiol Lett 1995; 133:105-11. [PMID: 8566694 DOI: 10.1111/j.1574-6968.1995.tb07869.x] [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: 01/31/2023] Open
Abstract
Electrophoretic analysis of outer membrane proteins showed that Salmonella typhi OmpC expression is not reciprocally regulated relative to OmpF as described for Escherichia coli and S. typhimurium. When bacteria were grown in minimal media, both OmpC and OmpF were repressed as the osmolarity increased. However, in Luria broth, expression of OmpC was slightly induced by osmolarity up to 0.3 osmM. Plasmids bearing E. coli ompC-lacZ or ompF-lacZ gene fusions were studied for their expression in S. typhi and E. coli. Under anaerobic growth conditions, expression of ompC-lacZ in S. typhi was maximal at 0.16 osmM, while in E. coli expression was maximal at 0.7 osmM. ompF-lacZ expression was similarly repressed by medium osmolarity and anaerobiosis in both species. In contrast, a drastic difference in the regulation of OmpF by temperature was observed; at 37 degrees C ompF-lacZ expression was repressed in E. coli, while in S. typhi it was induced.
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Affiliation(s)
- I Contreras
- Departamento de Biología Celular y Molecular, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile
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24
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Rosanas A, Barbé J, Gibert I. Cloning and sequencing of the gyrA gene from the plant pathogen Erwinia carotovora. Gene 1995; 161:11-4. [PMID: 7642123 DOI: 10.1016/0378-1119(95)00267-a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The gyrA gene of Erwinia carotovora subsp. carotovora has been cloned and sequenced. The deduced protein possessed 86% identity with the Escherichia coli GyrA protein. E. carotovora gyrA was also shown to complement an E. coli gyrA43ts mutation.
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Affiliation(s)
- A Rosanas
- Department of Genetics and Microbiology, Autonomous University of Barcelona, Bellaterra, Spain
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25
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Dorman CJ. 1995 Flemming Lecture. DNA topology and the global control of bacterial gene expression: implications for the regulation of virulence gene expression. MICROBIOLOGY (READING, ENGLAND) 1995; 141 ( Pt 6):1271-1280. [PMID: 7670631 DOI: 10.1099/13500872-141-6-1271] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Charles J Dorman
- Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College,Dublin 2,Republic of Ireland
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27
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Environmental Control of Virulence Functions and Signal Transduction in Yersinia Enterocolitica. SIGNAL TRANSDUCTION AND BACTERIAL VIRULENCE 1995. [DOI: 10.1007/978-3-662-22406-9_7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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28
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O'Byrne CP, Dorman CJ. Transcription of the Salmonella typhimurium spv virulence locus is regulated negatively by the nucleoid-associated protein H-NS. FEMS Microbiol Lett 1994; 121:99-105. [PMID: 8082832 DOI: 10.1111/j.1574-6968.1994.tb07082.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The possibility that the pleiotropic transcriptional regulator H-NS might play a role in regulating expression of the spv virulence locus of Salmonella typhimurium was investigated. A transposon insertion mutation in hns, the gene encoding H-NS, resulted in enhanced transcription of the spvR regulatory gene and the spvB structural gene in stationary phase cultures. Enhanced transcription was not detected prior to stationary phase, indicating that H-NS makes a negative contribution that is growth phase-specific to the control of spv transcription. When H-NS was over-expressed from a multicopy plasmid, the normal stationary phase induction of spv transcription seen in wild-type cells was abolished. spv transcription was also found to be modulated by growth medium osmolarity, a feature common to many H-NS-regulated genes. In addition, transcription of the spv genes was reduced in mutants with abnormal levels of DNA supercoiling.
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Affiliation(s)
- C P O'Byrne
- Department of Biochemistry, University of Dundee, UK
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29
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Affiliation(s)
- G R Cornelis
- Microbial Pathogenesis Unit, International Institute of Cellular and Molecular Pathology (ICP), Université Catholique de Louvain, Brussels, Belgium
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30
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Abstract
YmoA and Hha are highly similar bacterial proteins downregulating gene expression in Yersinia enterocolitica and Escherichia coli, respectively. The phenotype of ymoA mutants evokes that of mutants affected in some histone-like proteins. This paper describes complementation of a ymoA mutation in Y. enterocolitica by the hha gene from E. coli. We show that YmoA and Hha are not only very similar proteins but that they are functionally interchangeable. Genetic experiments indicate that Hha can also stimulate transposition events in vivo. By Southern blot analysis we detected hha-homologous genes at least in Citrobacter diversus, Shigella flexneri, Shigella dysenteriae, Klebsiella pneumoniae and Salmonella typhimurium. We suggest that both YmoA and Hha belong to a new family of proteins downregulating gene expression in different enterobacteria.
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Affiliation(s)
- A V Mikulskis
- Microbial Pathogenesis Unit, Université Catholique de Louvain, UCL 54.90, Brussels, Belgium
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