The ssgB gene, encoding a member of the regulon of stress-response sigma factor sigmaH, is essential for aerial mycelium septation in Streptomyces coelicolor A3(2).

The Streptomyces coelicolor A3(2) gene ssgB belongs to the regulon of stress-response sigma factor sigmaH. By integrative transformation via double cross-over, a stable null mutant of ssgB was obtained. This mutation had no obvious effect on vegetative growth, but critically affected aerial mycelium septation. The S. coelicolor ssgB mutant produced aerial hyphae without any signs of septation into spore compartments. The mutation was complemented in trans by wild-type ssgB including the sigmaH-dependent ssgBp promoter. The results proved that ssgB belongs a developmental branch of the sigmaH regulon.