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      Transcript changes in Vibrio cholerae in response to salt stress

      research-article
      , , , ,
      Gut Pathogens
      BioMed Central
      Vibrio cholerae, Salt stress, Transcription, PCR array

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          Abstract

          Vibrio cholerae, which is a serious human intestinal pathogen, often resides and thrives in estuaries but requires major self-regulation to overcome intestinal hyperosmotic stress or high salt stress in water and food. In the present study, we selected multiple O1 and O139 group V. cholerae strains that were isolated from different regions and during different years to study their salt tolerance. Based on the mechanisms that other bacteria use to respond to high salt stress, we selected salt stress-response related genes to study the mechanisms which V. cholerae responds to high salt stress.

          V. cholerae strains showed salt-resistance characteristics that varied in salt concentrations from 4% to 6%. However, group O1 and group O139 showed no significant difference in the degree of salt tolerance. The primary responses of bacteria to salt stress, including Na + exclusion, K + uptake and glutamate biosynthesis, were observed in V. cholerae strains. In addition, some sigma factors were up-regulated in V. cholerae strains, suggesting that V. cholerae may recruit common sigma factors to achieve an active salt stress response. However, some changes in gene transcript levels in response to salt stress in V. cholerae were strain-specific. In particular, hierarchical clustering of differentially expressed genes indicated that transcript levels of these genes were correlated with the degree of salt tolerance. Therefore, elevated transcript levels of some genes, including sigma factors and genes involved in peptidoglycan biosynthesis, may be due to the salt tolerance of strains. In addition, high salt-tolerant strains may recruit common as well as additional sigma factors to activate the salt stress response.

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          The online version of this article (doi:10.1186/s13099-014-0047-8) contains supplementary material, which is available to authorized users.

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          Most cited references26

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          Bacterial osmoadaptation: the role of osmolytes in bacterial stress and virulence.

          Two general strategies exist for the growth and survival of prokaryotes in environments of elevated osmolarity. The 'salt in cytoplasm' approach, which requires extensive structural modifications, is restricted mainly to members of the Halobacteriaceae. All other species have convergently evolved to cope with environments of elevated osmolarity by the accumulation of a restricted range of low molecular mass molecules, termed compatible solutes owing to their compatibility with cellular processes at high internal concentrations. Herein we review the molecular mechanisms governing the accumulation of these compounds, both in Gram-positive and Gram-negative bacteria, focusing specifically on the regulation of their transport/synthesis systems and the ability of these systems to sense and respond to changes in the osmolarity of the extracellular environment. Finally, we examine the current knowledge on the role of these osmostress responsive systems in contributing to the virulence potential of a number of pathogenic bacteria.
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            The extracytoplasmic function (ECF) sigma factors.

            Bacterial sigma (sigma) factors are an essential component of RNA polymerase and determine promoter selectivity. The substitution of one sigma factor for another can redirect some or all of the RNA polymerase in a cell to activate the transcription of genes that would otherwise be silent. As a class, alternative sigma factors play key roles in coordinating gene transcription during various stress responses and during morphological development. The extracytoplasmic function (ECF) sigma factors are small regulatory proteins that are quite divergent in sequence relative to most other sigma factors. Many bacteria, particularly those with more complex genomes, contain multiple ECF sigma factors and these regulators often outnumber all other types of sigma factor combined. Examples include Bacillus subtilis (7 ECF sigma factors), Mycobacterium tuberculosis (10), Caulobacter crescentus (13), Pseudomonas aeruginosa (approximately 19), and Streptomyces coelicolor (approximately 50). The roles and mechanisms of regulation for these various ECF sigma factors are largely unknown, but significant progress has been made in selected systems. As a general trend, most ECF sigma factors are cotranscribed with one or more negative regulators. Often, these include a transmembrane protein functioning as an anti-sigma factor that binds, and inhibits, the cognate sigma factor. Upon receiving a stimulus from the environment, the sigma factor is released and can bind to RNA polymerase to stimulate transcription. In many ways, these anti-sigma:sigma pairs are analogous to the more familiar two-component regulatory systems consisting of a transmembrane histidine protein kinase and a DNA-binding response regulator. Both are mechanisms of coordinating a cytoplasmic transcriptional response to signals perceived by protein domains external to the cell membrane. Here, I review current knowledge of some of the better characterized ECF sigma factors, discuss the variety of experimental approaches that have proven productive in defining the roles of ECF sigma factors, and present some unifying themes that are beginning to emerge as more systems are studied.
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              The heat shock response of Escherichia coli.

              A large variety of stress conditions including physicochemical factors induce the synthesis of more than 20 heat shock proteins (HSPs). In E. coli, the heat shock response to temperature upshift from 30 to 42 degrees C consists of the rapid induction of these HSPs, followed by an adaptation period where the rate of HSP synthesis decreases to reach a new steady-state level. Major HSPs are molecular chaperones, including DnaK, DnaJ and GrpE, and GroEL and GroES, and proteases. They constitute the two major chaperone systems of E. coli (15-20% of total protein at 46 degrees C). They are important for cell survival, since they play a role in preventing aggregation and refolding proteins. The E. coli heat shock response is positively controlled at the transcriptional level by the product of the rpoH gene, the heat shock promoter-specific sigma32 subunit of RNA polymerase. Because of its rapid turn-over, the cellular concentration of sigma32 is very low under steady-state conditions (10-30 copies/cell at 30 degrees C) and is limiting for heat shock gene transcription. The heat shock response is induced as a consequence of a rapid increase in sigma32 levels and stimulation of sigma32 activity. The shut off of the response occurs as a consequence of declining sigma32 levels and inhibition of sigma32 activity. Stress-dependent changes in heat shock gene expression are mediated by the antagonistic action of sigma32 and negative modulators which act upon sigma32. These modulators are the DnaK chaperone system which inactivate sigma32 by direct association and mediate its degradation by proteases. Degradation of sigma32 is mediated mainly by FtsH (HflB), an ATP-dependent metallo-protease associated with the inner membrane. There is increasing evidence that the sequestration of the DnaK chaperone system through binding to misfolded proteins is a direct determinant of the modulation of the heat shock genes expression. A central open question is the identity of the binding sites within sigma32 for DnaK, DnaJ, FtsH and the RNA polymerase, and the functional interplay between these sites. We have studied the role of two distinct regions of sigma32 in its activity and stability control: region C and the C-terminal part. Both regions are involved in RNA polymerase binding.
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                Author and article information

                Contributors
                fuxiuping313@sina.com
                liangweili@icdc.cn
                dupengcheng@icdc.cn
                yanmeiying@icdc.cn
                kanbiao@icdc.cn
                Journal
                Gut Pathog
                Gut Pathog
                Gut Pathogens
                BioMed Central (London )
                1757-4749
                30 December 2014
                30 December 2014
                2014
                : 6
                : 1
                : 47
                Affiliations
                [ ]State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, 155, Changbai Road, Changping, Beijing 102206 China
                [ ]Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Hangzhou, 310006 China
                Article
                47
                10.1186/s13099-014-0047-8
                4293811
                65d1548b-1ea8-4cfd-b088-01335e90098a
                © Fu et al.; licensee Biomed Central. 2014

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 24 October 2014
                : 13 December 2014
                Categories
                Research
                Custom metadata
                © The Author(s) 2014

                Gastroenterology & Hepatology
                vibrio cholerae,salt stress,transcription,pcr array
                Gastroenterology & Hepatology
                vibrio cholerae, salt stress, transcription, pcr array

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