The pst operon of Bacillus subtilis is specifically induced by alkali stress.

To cope with a sudden increase in the external pH value to 8.9, Bacillus subtilis cells induce about 80 genes which can be divided into two classes. Most of these genes are members of the sigma(W) regulon, while some are under the control of so-far-unknown transcriptional regulators. The genes of the pst operon belong to the second class. Here, we attempted to answer the questions of why and how the genes of this operon are induced. Using transcriptional fusions to two of the five genes of this operon, we confirmed their induction after alkali stress. Furthermore, a Northern blot experiment revealed that the complete operon was alkali inducible, that the transcriptional start site used was identical to that used after phosphate starvation, and that induction was prevented in a phoR background. Most interestingly, increasing the phosphate concentration within the medium prevented alkali induction of the pst operon, and phoA, another member of the PhoRP regulon, did not respond to alkali stress. In the end, we showed that alkali treatment completely prevented phosphate uptake. These results are discussed to explain alkali induction of the pst operon.