Abstract
BackgroundThe human pathogen Vibrio cholerae normally enters the developmental program of natural competence for transformation after colonizing chitinous surfaces. Natural competence is regulated by at least three pathways in this organism: chitin sensing/degradation, quorum sensing and carbon catabolite repression (CCR). The cyclic adenosine monophosphate (cAMP) receptor protein CRP, which is the global regulator of CCR, binds to regulatory DNA elements called CRP sites when in complex with cAMP. Previous studies in Haemophilus influenzae suggested that the CRP protein binds competence-specific CRP-S sites under competence-inducing conditions, most likely in concert with the master regulator of transformation Sxy/TfoX.ResultsIn this study, we investigated the regulation of the competence genes qstR and comEA as an example of the complex process that controls competence gene activation in V. cholerae. We identified previously unrecognized putative CRP-S sites upstream of both genes. Deletion of these motifs significantly impaired natural transformability. Moreover, site-directed mutagenesis of these sites resulted in altered gene expression. This altered gene expression also correlated directly with protein levels, bacterial capacity for DNA uptake, and natural transformability.ConclusionsBased on the data provided in this study we suggest that the identified sites are important for the expression of the competence genes qstR and comEA and therefore for natural transformability of V. cholerae even though the motifs might not reflect bona fide CRP-S sites.
Highlights
The human pathogen Vibrio cholerae normally enters the developmental program of natural competence for transformation after colonizing chitinous surfaces
We demonstrated that overexpression of qstR was sufficient to increase the abundance of the comEA transcripts, not to the same level observed under competence-inducing conditions
Regulation of comEA by QstR and TfoX/CRP-cyclic adenosine monophosphate (cAMP) From previous studies it was known that the expression of comEA is dependent on a) the master regulator of transformation, TfoX; b) the CRP-cAMP complex; and c) the transcription factor QstR [4,22,23] (Figure 1)
Summary
The human pathogen Vibrio cholerae normally enters the developmental program of natural competence for transformation after colonizing chitinous surfaces. Natural competence is regulated by at least three pathways in this organism: chitin sensing/degradation, quorum sensing and carbon catabolite repression (CCR). In addition to its role as a nutrient source, chitin induces natural competence for transformation in V. cholerae [4] and other Vibrio species (reviewed by [5]). In addition to TfoX expression, pathways that regulate quorum sensing (QS) and carbon catabolite repression (CCR) are necessary to induce the competence regulon of V. cholerae [11,23] (Figure 1). HapR regulates natural transformation by direct repression of dns and concomitantly with TfoX-mediated induction, directly drives the expression of qstR, which encodes the newly identified transcription factor QstR [22] (Figure 1). The contribution of QstR to natural transformation was recently confirmed by Dalia et al using a genome-wide transposon sequencing (Tn-seq) screen [36]
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