Transcriptional responses during outgrowth of Bacillus subtilis endospores

The Bacillus subtilis 168 genome contains an array of alternative sigma factors, many of which play important roles in reprogramming expression during stress and sporulation. The role of the different sigma factors during outgrowth, when the germinated endospore is converted back to a vegetative cell, is less well characterized. The activity of the alternative sigma factors sigmaB, sigmaD and sigmaH during endospore outgrowth was analysed by Northern blotting and lacZ reporter assays. While sigmaD and sigmaH were transcriptionally active during outgrowth, sigmaB-dependent transcription was not observed until after the first cell division, when growth slowed. Using an IPTG-controllable copy of sigA, an optimal level of expression was required to maintain growth rate at the end of outgrowth. The genes encoding the putative extracytoplasmic function (ECF) sigma factors sigmaI, sigmaV, sigmaW, sigmaZ and YlaC were insertionally inactivated using pMUTIN4. These strains, together with sigM and sigX mutants, were tested to determine their role and measure their expression during endospore outgrowth. Transcripts or beta-galactosidase activity were observed for each of the ECF sigma factors early after germination. With the exception of MJH003 (sigM), which showed an exacerbated salt stress defect, inactivation of the ECF sigma factor genes did not affect outgrowth in the conditions tested.