The primary role of comA in establishment of the competent state in Bacillus subtilis is to activate expression of srfA

The establishment of genetic competence in Bacillus subtilis requires the genes of the competence regulon which function in the binding, processing, and transport of DNA. Their expression is governed by multiple regulatory pathways that are composed of the comA, comP, sin, abrB, spo0H, spo0K, spo0A, degU, and srfA gene products. Among these, srfA is thought to occupy an intermediate position in one of the pathways that controls late competence gene expression. The full expression of srfA requires the gene products of comP, comA, and spo0K. To determine the role of these genes in the regulation of competence development, the expression of the srfA operon was placed under control of the isopropyl-β-D-thiogalactopyranoside (IPTG)-inducible promoter P(spac) and the expression of the P(spac)-srfA construct was examined in mutants blocked in early competence. By monitoring the IPTG-induced expression of P(spac)-srfA with a srfA-lacZ operon fusion, it was observed that srfA expression was no longer dependent on the products of comP, comA, and spo0K. Production of the lipopeptide antibiotic surfactin in P(spac)-srfA-bearing cells was induced in the presence of IPTG and was independent of ComP and ComA. Competence development was induced by IPTG and was independent of comP, comA, and spo0K in cells carrying P(spac)-srfA. These results suggest that the ComP-ComA signal transduction pathway as well as Spo0K is required for the expression of srfA in the regulatory cascade of competence development. Studies of P(spac)-srfA also examined the involvement of srfA in the growth stage-specific and nutritional regulation of a late competence gene.