Conserved type VI secretion regulation in diverse Vibrio species by the regulatory proteins TfoX and TfoY

Bacteria of the genus Vibrio are common members of aquatic environments where they compete with other prokaryotes and defend themselves against grazing predators. A macromolecular protein complex called the type VI secretion system (T6SS) is used for both purposes. Previous research showed that the sole T6SS of the human pathogen V. cholerae is induced by extracellular (chitin) or intracellular (low c-di-GMP levels) cues and that these cues lead to distinctive signalling pathways for which the proteins TfoX and TfoY serve as master regulators. In this study, we tested whether the TfoX- and TfoY-mediated regulation of T6SS was conserved in non-cholera species, and if so, how these regulators affected the production of individual T6SSs in double-armed vibrios. We show that, alongside representative competence genes, TfoX regulates at least one T6SS in all tested Vibrio species. TfoY, on the other hand, fostered motility in all vibrios but had a more versatile T6SS response in that it did not foster T6SS-mediated killing in V. fischeri while it induced both systems in V. alginolyticus. Collectively, our data provide evidence that the TfoX- and TfoY-mediated signalling pathways are mostly conserved in diverse Vibrio species and important for signal-specific T6SS induction.

Ecological implications of gene regulation by TfoX and TfoY among diverse Vibrio species

Melanie Blokesch, Esther Jeanne Collas, Noémie Matthey, Lisa Christina Metzger, Candice Stoudmann

Bacteria of the genus Vibrio are common members of aquatic environments where they compete with other prokaryotes and defend themselves against grazing predators. A macromolecular protein complex called the type VI secretion system (T6SS) is used for both purposes. Previous research showed that the sole T6SS of the human pathogen V. cholerae is induced by extracellular (chitin) or intracellular (low c‐di‐GMP levels) cues and that these cues lead to distinctive signalling pathways for which the proteins TfoX and TfoY serve as master regulators. In this study, we tested whether the TfoX‐ and TfoY‐mediated regulation of T6SS, concomitantly with natural competence or motility, was conserved in non‐cholera Vibrio species, and if so, how these regulators affected the production of individual T6SSs in double‐armed vibrios. We show that, alongside representative competence genes, TfoX regulates at least one T6SS in all tested Vibrio species. TfoY, on the other hand, fostered motility in all vibrios but had a more versatile T6SS response in that it did not foster T6SS‐mediated killing in all tested vibrios. Collectively, our data provide evidence that the TfoX‐ and TfoY‐mediated signalling pathways are mostly conserved in diverse Vibrio species and important for signal‐specific T6SS induction.

2019

Chitin colonization, chitin degradation and chitin-induced natural competence of Vibrio cholerae are subject to catabolite repression

Melanie Blokesch

Although Vibrio cholerae is a human pathogen its primary habitat are aquatic environments. In this environment, V. cholerae takes advantage of the abundance of zooplankton, whose chitinous exoskeletons provide a nutritious surface. Chitin also induces the developmental programme of natural competence in several species of the genus Vibrio. Because the chitin surface can serve as the sole carbon source for V. cholerae, the link between carbon catabolite repression and chitin-induced natural competence for transformation was investigated in this study. Provision of competing phosphoenolpyruvate: carbohydrate phosphotransferase system (PTS)-dependent carbon sources in addition to chitin significantly lowered natural transformability. These sugars are known to interfere with the accumulation of 3,5- cyclic AMP (cAMP); therefore, the contributions of the cAMP-producing enzyme, adenylate cyclase and the cAMP receptor protein (CRP) to chitin surface colonization, chitin degradation and natural transformation were also analysed. The results provided here indicate that cAMP and CRP are important in at least three interlinked areas of the chitin-induced natural competence programme. First, cAMP and CRP are required for the efficient colonization of the chitin surface; second both contribute to chitin degradation and utilization, and third, cAMP plus CRP play a role in increasing competence gene expression. These findings highlight the complex regulatory circuit of chitininduced natural competence in V. cholerae.

Wiley-Blackwell2012

Quorum Sensing Contributes to Natural Transformation of Vibrio cholerae in a Species-Specific Manner

Melanie Blokesch, Patrick Martin Seitz, Gaia Francesca Marianne Suckow

Although it is a human pathogen, Vibrio cholerae is a regular member of aquatic habitats, such as coastal regions and estuaries. Within these environments, V. cholerae often takes advantage of the abundance of zooplankton and their chitinous molts as a nutritious surface on which the bacteria can form biofilms. Chitin also induces the developmental program of natural competence for transformation in several species of the genus Vibrio. In this study, we show that V. cholerae does not distinguish between species-specific and non-species-specific DNA at the level of DNA uptake. This is in contrast to what has been shown for other Gram-negative bacteria, such as Neisseria gonorrhoeae and Haemophilus influenzae. However, species specificity with respect to natural transformation still occurs in V. cholerae. This is based on a positive correlation between quorum sensing and natural transformation. Using mutant-strain analysis, cross-feeding experiments, and synthetic cholera autoinducer-1 (CAI-1), we provide strong evidence that the species-specific signaling molecule CAI-1 plays a major role in natural competence for transformation. We suggest that CAI-1 can be considered a competence pheromone.

American Society for Microbiology2011