Global transcriptional response of Bacillus subtilis to heat shock

In response to heat stress, Bacillus subtilis activates the transcription o f well over 100 different genes. Many of these genes are members of a gener al stress response regulon controlled by the secondary sigma factor, sigma (B), while others are under control of the HrcA or CtsR heat shock regulato rs. We have used DNA microarrays to monitor the global transcriptional resp onse to heat shock. We find strong induction of known sigma (B)-dependent g enes with a characteristic rapid induction followed by a return to near pre stimulus levels. The HrcA and CtsR regulons are also induced, but with some what slower kinetics. Analysis of DNA sequences proximal to newly identifie d heat-induced genes leads us to propose similar to 70 additional members o f the sigma (B) regulon. We have also identified numerous heat-induced gene s that are not members of known heat shock regulons. Notably, we observe ve ry strong induction of arginine biosynthesis and transport operons. Inducti on of several genes was confirmed by quantitative reverse transcriptase PCR . In addition, the transcriptional responses measured by microarray hybridi zation compare favorably with the numerous previous studies of heat shock i n this organism. Since many different conditions elicit both specific and g eneral stress responses, knowledge of the heat-induced general stress respo nse reported here will be helpful for interpreting future microarray studie s of other stress responses.