The distinct PhoPR mediated responses to phosphate limitation in Bacillus subtilis subspecies subtilis and spizizenii stem from differences in wall teichoic acid composition and metabolism.

The PhoPR-mediated response to phosphate limitation (PHO response) in Bacillus subtilis subsp subtilis is amplified and maintained by reducing the level of Lipid V composed of poly(glycerol phosphate), a wall teichoic acid (WTA) biosynthetic intermediate that inhibits PhoR autokinase activity. However, the reduction in Lipid V level is effected by activated PhoP∼P, raising the question of how the PHO response is first initiated. Furthermore, that WTA is composed of poly(ribitol phosphate) in Bacillus subtilis subsp spizizenii prompted an investigation of how the PHO response is regulated in that bacterium. We report that the PHO responses of B. subtilis subsp subtilis and subsp spizizenii are distinct. The PhoR kinases of the two B. subtilis subspecies are functionally equivalent and are activated either by the TagA/TarA or TagB/TarB enzyme product. However, they are inhibited by Lipid V composed of poly(glycerol phosphate) but not by Lipid V composed of poly(ribitol phosphate). Therefore, the distinctive PHO responses of these B. subtilis subspecies stem from the differential sensitivity of PhoR kinases to the polyol composition of Lipid V and from the genomic organization of WTA biosynthetic genes and the regulation of their expression.