Stripping Bacillus: ComK auto‐stimulation is responsible for the bistable response in competence development

In Bacillus subtilis competence for genetic transformation develops only in a subpopulation of cells in an isogenic culture. The molecular mechanisms underlying this phenotypic heterogeneity are unknown. In this study, we stepwise simplify the signal transduction cascade leading to competence, yielding a strain devoid of all regulatory inputs for this process that have been identified so far. We demonstrate that auto‐stimulation of ComK, the master regulator for competence development, is essential and in itself can be sufficient to generate a bistable expression pattern. We argue that transcriptional regulation determines the threshold of ComK to initiate the auto‐stimulatory response, and that the basal level of ComK (in a wild‐type strain governed by MecA‐mediated proteolytic control) determines the fraction of cells that reach this threshold, and thus develop competence.

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