Regulation of myo-inositol catabolism by a GntR-type repressor SCO6974 in Streptomyces coelicolor.

Abstract

Myo-inositol is important for Streptomyces growth and morphological differentiation. Genomic sequence analysis revealed a myo-inositol catabolic gene cluster in Streptomyces coelicolor. Disruption of the corresponding genes in this cluster abolished the bacterial growth on myo-inositol as a single carbon source. The transcriptions of these genes were remarkably enhanced by addition of myo-inositol in minimal medium. A putative regulatory gene SCO6974, encoding a GntR family protein, is situated in the cluster. Disruption of SCO6974 significantly enhanced the transcription of myo-inositol catabolic genes. SCO6974 was shown to interact with the promoter regions of myo-inositol catabolic genes using electrophoretic mobility shift assays. DNase I footprinting assays demonstrated that SCO6974 recognized a conserved palindromic sequence (A/T)TGT(A/C)N(G/T)(G/T)ACA(A/T). Base substitution of the conserved sequence completely abolished the binding of SCO6974 to the targets demonstrating that SCO6974 directly represses the transcriptions of myo-inositol catabolic genes. Furthermore, the disruption of SCO6974 was correlated with a reduced sporulation of S. coelicolor in mannitol soya flour medium and with the overproduction of actinorhodin and calcium-dependent antibiotic. The addition of myo-inositol suppressed the sporulation deficiency of the mutant, indicating that the effect could be related to a shortage in myo-inositol due to its enhanced catabolism in this strain. This enhanced myo-inositol catabolism likely yields dihydroxyacetone phosphate and acetyl-CoA that are indirect or direct precursors of the overproduced antibiotics.