Regulation of natural competence by the orphan two-component system sensor kinase ChiS involves a non-canonical transmembrane regulator in Vibrio cholerae.
ABSTRACT In Vibrio cholerae, 41 chitin-inducible genes, including the genes involved in natural competence for DNA uptake, are governed by the orphan two-component system (TCS) sensor kinase ChiS. However, the mechanism by which ChiS controls the expression of these genes is currently unknown. Here, we report the involvement of a novel transcriptional factor termed 'TfoS' in this process. TfoS is a transmembrane protein that contains a large periplasmic domain and a cytoplasmic AraC-type DNA-binding domain, but lacks TCS signature domains. Inactivation of tfoS abolished natural competence as well as transcription of the tfoR gene encoding a chitin-induced small RNA essential for competence gene expression. A TfoS fragment containing the DNA-binding domain specifically bound to and activated transcription from the tfoR promoter. Intracellular TfoS levels were unaffected by disruption of chiS and co-expression of TfoS and ChiS in Escherichia coli recovered transcription of the chromosomally integrated tfoR::lacZ gene, suggesting that TfoS is post-translationally modulated by ChiS during transcriptional activation; however, this regulation persisted when the canonical phosphorelay residues of ChiS were mutated. The results presented here suggest that ChiS operates a chitin-induced non-canonical signal transduction cascade through TfoS, leading to transcriptional activation of tfoR.
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ABSTRACT: Bacteria use intricately interconnected mechanisms acting at the transcriptional and post-transcriptional level to adjust gene expression to their needs. An intriguing example found in the chitosugar utilization systems of Escherichia coli and Salmonella is uncovered in a study by Plumbridge and colleagues in the current issue of Molecular Microbiology. Three transcription factors (TFs), a small regulatory RNA (sRNA) and a sRNA trap cooperate to set thresholds and dynamics in regulation of chitosugar utilization. Specifically, under inducing conditions a decoy site on the polycistronic chitobiose (chbBCARFG) mRNA sequesters sRNA ChiX, which represses synthesis of the separately encoded chitoporin ChiP. Basepairing of ChiX with its decoy has no role for the chb genes themselves when the mRNA is in excess. In the absence of substrate, however, this base-pairing tightly represses chbC encoding a subunit of the chitosugar transporter. Thus, one and the same sRNA/mRNA interaction serves different regulatory functions under different environmental conditions. The employment of RNA decoys to control the activities of post-transcriptional regulators themselves is an increasingly recognized mechanism in gene regulation. Another observation in the current study highlights the possibility that decoy sites might even exist on the DNA controlling the availability of TFs for their target promoters.Molecular Microbiology 04/2014; · 5.03 Impact Factor
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ABSTRACT: В настоящем обзоре представлены литературные данные, отражающие определяющую роль поверхностных водоемов с компонентами экосистем, существенно влияющих на основные эндемические и эпидемические проявления холеры, в экологии вибриона эльтор. Несмотря на то, что поверхностные водоемы признаны Комитетом экспертов ВОЗ (1968) самостоятельной заражающей средой, по существующей в России классификации инфекционных болезней холера относится к антропонозам с фекально-оральным механизмом передачи и единственным источником инфекции. В работе рассматриваются разные взгляды на холеру: от природной очаговости холеры и её сапронозной природы, до её принадлежности к сапрозооантропонозам. Описаны типы взаимоотношений холерного вибриона с представителями водной ок-ружающей среды, определена роль в его жизненном цикле высших водных растений, фитопланктона, рыб, ракообразных и водоплавающих птиц. Обосновывается целесообразность введения в классификацию инфекционных болезней дополнительных классов (подклассов) и отнесения холеры в раздел сапрозооантропонозов. Abstract Literary data reflecting the crucial role of surface water reservoirs with ecosystem components essentially influencing on the main endemic and epidemic cholera manifestations in Vibrio cholerae ecology are reviewed. In spite of the fact that the WHO Committee of Experts (1968) has recognized surface water reservoirs as an independent infecting environment, according to the Russian classification of infectious diseases the cholera is referred to anthroponoses with fecal-oral transmission and an unique source of an infection. Various views to cholera are considered in the paper: from natural cholera focality and its sapronosis nature to its belonging to saprozooanthroponosis. Types of mutual relations of V. cholerae with water environment representatives are described. The role of the higher water plants, phytoplankton, fishes, crustaceans and waterfowl in V. cholerae life cycle is showed. Reasonability of introduction of additional classes (subclasses) in classification of infectious diseases and cholera attribution to saprozooanthroponoses section is validated.Epidemiology & Vaccinal Prevention. 09/2014; 4(77):17-23.
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ABSTRACT: Natural bacterial transformation involves the internalization and chromosomal integration of DNA and has now been documented in ∼80 species. Recent advances have established that phylogenetically distant species share conserved uptake and processing proteins but differ in the inducing cues and regulatory mechanisms that are involved. In this Review, we highlight divergent and common principles that govern the transformation process in different bacteria. We discuss how this cumulative knowledge enables the prediction of new transformable species and supports the idea that the main role of internalized DNA is in the generation of genetic diversity or in chromosome repair rather than in nutrition.Nature Reviews Microbiology 02/2014; · 22.49 Impact Factor