CIpP modulates the activity of the Bacillus subtilis stress response transcription factor, σB

The general stress regulon of Bacillus subtilis is controlled by the activity state of sigma(B), a transcription factor that is switched on following exposure to either physical or nutritional stress. ClpP is the proteolytic component of an ATP-dependent protease that is essential for the proper regulation of multiple adaptive responses in B. subtilis. Among the proteins whose abundance increases in ClpP-B. subtilis are several known to depend on or B for their expression. In the current work we examine the relationship of CIpP to the activity of sigma(B). The data reveal that the loss of CIpP in otherwise wild-type B. subtilis results in a small increase in sigma(B) activity during growth and a marked enhancement of sigma(B) activity following its induction by either physical or nutritional stress. It appears to be the persistence of sigma(B,)s activity rather than its induction that is principally affected by the loss of CIpP. sigma(B)-dependent reporter gene activity rose in parallel in CIpP(+) and ClpP(-) B. subtilis strains but failed to display its normal transience in the ClpP- strain. The putative CIpP targets are likely to be stress generated and novel. Enhanced sigma(B) activity in ClpP(-) B. subtilis was triggered by physical stress but not by the induced synthesis of the physical stress pathway's positive regulator (RsbT). In addition, Western blot analyses failed to detect differences in the levels of the principal known sigma(B) regulators in CipP(+) and CIpP(-) B. subtilis strains. The data suggest a model in which CIpP facilitates the turnover of stress-generated factors, which persist in ClpP's absence to stimulate ongoing sigma(B) activity.