Bacillus subtilis operon under the dual control of the general stress transcription factor sigma(B) and the sporulation transcription factor sigma(H)

The sigma(B) transcription factor of Bacillus subtilis is activated in response to a variety of environmental stresses, including those imposed by entry into the stationary-growth phase, and by heat, salt or ethanol challenge to logarithmically growing cells. Although sigma(B) is thought to control a general stress regulon, the range of cellular functions it directs remains largely unknown. Our approach to understand the physiological role of sigma(B) is to characterize genes that require this factor for all or part of their expression, i.e. the csb genes. In this study, we report that the transposon insertion csb40::Tn917lac identifies an operon with three open reading frames, the second of which resembles plant proteins induced by desiccation stress. Primer-extension and operon-fusion experiments showed that the csb40 operon has a sigma(B)-dependent promoter which is strongly induced by the addition of salt to logarithmically growing cells. The csb40 operon also has a second, sigma(H)-dependent promoter that is unaffected by salt addition. These results provide support for the hypothesis that sigma(B) controls a general stress regulon, and indicate that the sigma(B) and sigma(H) regulons partly overlap. We suggest that in addition to its acknowledged role in the sporulation process, sigma(H) is also involved in controlling a subclass of genes that are broadly involved in a general stress response.