Multi-layered inhibition of Streptomyces development: BldO is a dedicated repressor of whiB

BldD-(c-di-GMP) sits on top of the regulatory network that controls differentiation in Streptomyces, repressing a large regulon of developmental genes when the bacteria are growing vegetatively. In this way, BldD functions as an inhibitor that blocks the initiation of sporulation. Here, we report the identification and characterisation of BldO, an additional developmental repressor that acts to sustain vegetative growth and prevent entry into sporulation. However, unlike the pleiotropic regulator BldD, we show that BldO functions as the dedicated repressor of a single key target gene, whiB, and that deletion of bldO or constitutive expression of whiB is sufficient to induce precocious hypersporulation.