Pleiotropic Control of Secondary Metabolism and Morphological Development by KsbC, a Butyrolactone Autoregulator Receptor Homologue in Kitasatospora setae

Abstract

ABSTRACTThe γ-butyrolactone autoregulator signaling cascades have been shown to control secondary metabolism and/or morphological development among manyStreptomycesspecies. However, the conservation and variation of the regulatory systems among actinomycetes remain to be clarified. The genome sequence ofKitasatospora setae, which also belongs to the familyStreptomycetaceaecontaining the genusStreptomyces, has revealed the presence of three homologues of the autoregulator receptor: KsbA, which has previously been confirmed to be involved only in secondary metabolism; KsbB; and KsbC. We describe here the characterization ofksbC, whose regulatory cluster closely resembles theStreptomyces virginiae barAlocus responsible for the autoregulator signaling cascade. Deletion of the geneksbCresulted in lowered production of bafilomycin and a defect of aerial mycelium formation, together with the early and enhanced production of a novel β-carboline alkaloid named kitasetaline. A putative kitasetaline biosynthetic gene cluster was identified, and its expression in a heterologous host led to the production of kitasetaline together with JBIR-133, the production of which is also detected in theksbCdisruptant, and JBIR-134 as novel β-carboline alkaloids, indicating that these genes were biosynthetic genes for β-carboline alkaloid and thus are the first such genes to be discovered in bacteria.