A pho regulon promoter induced under sporulation conditions

Sporulation-induced alkaline phosphatases (APases) of Bacillus subtilis require the products of the sporulation stage-0 genes and certain stage-II genes, including the spoIIA operon, for induction. Mutations in either sapA or sapB bypass this requirement [Piggot and Taylor, J. Gen. Microbiol. 10 (1977) 69-80], resulting in APase production in a spoIIA sapA or spoIIA sapB strain, under sporulation conditions. B. subtilis has multiple structural genes encoding APases, which are induced either by phosphate starvation or during sporulation, or under both conditions. We report studies designed to determine which APase(s) were being expressed in the sap mutants, and from which promoters. phoB (formerly phoAIII), one of the structural genes encoding an APase in B. subtilis, is expressed under both sporulation and phosphate starvation conditions, but from separate promoters [Chesnut et al., Mol. Microbiol. 5 (1991) 2181-2190]. The spoIIA sapA and spoIIA sapB strains express phoB under sporulation conditions. Interestingly, the expression of phoB during sporulation was from Pv, the phosphate starvation-inducible promoter of phoB, rather than from Ps, the sporulation-specific promoter. Since the induction of phosphate starvation-inducible promoters during phosphate limitation requires the phoPR operon [Miki et al., Genetics 52 (1965) 1093-1100], we asked if the phoPR products were involved in regulating Pv expression under sporulation conditions. The phoPR genes are transcribed under sporulation conditions, regulated by sapA and sapB under sporulation conditions, and required for expression from Pv under sporulation conditions.