ClpP modulates the activity of the Bacillus subtilis stress response transcription factor, ^B

Department of Microbiology & Immunology-MC7758, University of Texas Health Science Center, San Antonio, TX USA 78229-3900; Institute for Microbiology and Interfacultary Institute for Genetics and Functional Genomics, Ernst-Moritz-Arndt-University, Greifswald, Germany

^* To whom correspondence should be addressed. Email: haldenwang{at}uthscsa.edu.

	Abstract

The general stress regulon of Bacillus subtilis is controlled by the activity state of ^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 ^B for their expression. In the current work we examine the relationship of ClpP to ^B's activity. The data reveal that the loss of ClpP in otherwise wildtype B. subtilis results in a small increase in ^B activity during growth, and a marked enhancement of ^B activity following its induction by either physical or nutritional stress. It appears to be the persistence of ^B's activity rather than its induction that is principally affected by the loss of ClpP. ^B dependent reporter gene activity rose in parallel in ClpP^+/- B. subtilis, but failed to display its normal transience in the ClpP- strain. The putative ClpP targets are likely to be stress-generated and novel. Enhanced ^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 ^B regulators in ClpP^+/- B. subtilis. The data suggest a model in which ClpP facilitates the turnover of stress generated factors, which persist in ClpP's absence to stimulate ongoing ^B activity.