Transcriptional regulation of swrAA, a gene involved in motility and in the synthesis of gamma-poly-glutamic acid in Bacillus subtilis

We demonstrate that transcription of the gene swrAA, required for swarming migration in B. subtilis, is driven by two promoters: a sigD-dependent promoter, active during growth in liquid LB medium, and a putative sigA-dependent promoter, active in the presence of the phosphorylated form of the response regulator DegU and in swarming conditions. The existence of a positive feed-back loop, with SwrAA enhancing sigD expression and being in turn SigD-dependent, is confirmed by the level of the swrA operon transcription in swrAA+ and swrAA- strains. Furthermore, our data indicate that DegU is necessary for swimming as well as for swarming and this requirement is independent from swrAA transcription, since SwrAA over-expression does not restore motility in strains carrying a deletion of the two component system degSdegU. Besides motility, we show that SwrAA and DegU, the latter in the constitutively active form degU32(Hy), are both necessary for the activation of the pgs operon, driving the synthesis of gamma-poly-glutamic acid (PGA).