Abstract

The alternative transcription factor rB of Bacillus subtilis is activated during the stationary growth phase by a regulatory network responsive to stationary-phase signals. On the basis of the results reported here, we propose that uB controls a general stress regulon that is induced when cells encounter a variety of growth-limiting conditions. Expression of genes controlled by rB, including the ctc gene and the sigB operon that codes for crB and its associated regulatory proteins, was dramatically induced in both the exponential and stationary phases by environmental challenges known to elicit a general stress response. After cells were subjected to salt stress, the increased expression of lacZ transcriptional fusions to the ctc and sigB genes was entirely dependent on CB, and primer extension experiments confirmed that the CrB-dependent transcriptional start site was used during salt induction of sigB operon expression. Western blotting (immunoblotting) experiments measuring the levels of CrB protein indicated that ethanol addition and heat stress also induced crB activity during logarithmic growth. Salt and ethanol induction during logarithmic growth required RsbV, the positive regulator of o'B activity that is normally necessary for activity in stationary-phase cells. However, heat induction of C'B activity was largely independent of RsbV, indicating that there are two distinct pathways by which these environmental signals are conveyed to the transcriptional apparatus. Sensing and adapting to fluctuations in environmental con-