Escape from the competence state in Streptococcus mutans is governed by the bacterial population density

The objective of the present work was to help decipher the molecular mechanisms regulating the escape from the competence state in Streptococcus mutans, the principal etiological agent responsible for tooth decay in humans. Our results showed that the cessation of competence in S. mutans was abrupt, and did not involve the accumulation of a competence inhibitor nor the depletion of a competence activator in the extracellular environment. The competence state was repressed at high cell population density via concomitant repression of sigX gene encoding the master regulator of the competence regulon. Co‐culture experiments performed with oral and non‐oral bacteria showed that S. mutans assesses its own population density and also the microbial density of its surroundings to regulate its competence escape. Interestingly, neither the intra‐species and extra‐species quorum‐sensing systems nor the other 13 two‐component regulatory systems identified in S. mutans were involved in the cell‐density‐dependent escape of the competence state. Altogether, our results suggest a complex mechanism regulating the competence shut‐off involving cell‐density‐dependent repression of sigX through an as yet undefined system, and possibly SigX protein stability.
Source: Oral Microbiology and Immunology - Category: Microbiology Authors: Tags: Original Article Source Type: research