Catabolite-induced repression of sporulation in Bacillus subtilis

In response to nutrient limitations, Bacillus subtilis cells undergo a series of morphological and genetic changes that culminate in the formation of endospores. Conversely, excess catabolites inhibit sporulation. It has been demonstrated previously that excess catabolites caused a decrease in culture medium pH in a process that required functional AbrB. Culture medium acidification was also shown to inhibit sigmaH-dependent sporulation gene expression. The studies reported here investigate the effects of AbrB-mediated pH sensing on B. subtilis developmental competence. We have found that neither addition of a pH stabilizer, MOPS (pH 7.5), nor null mutations in abrB blocked catabolite repression of sporulation. Moreover, catabolite-induced culture medium acidification was observed in cultures of catabolite-resistant sporulation mutants, crsA47, rvtA11, and hpr-16, despite their efficient sporulation. These results suggest that AbrB-mediated pH sensing is not the only mechanism regulating catabolite repression of sporulation. The AbrB pathway may function to channel cells toward genetic competence, as opposed to other postexponential differentiation pathways.