cvhA gene of Streptomyces hygroscopicus 10-22 encodes a negative regulator for mycelia development

A five-gene cluster cvhABCDE was identified from Streptomyces hygroscopicus 10-22. As the first gene of this cluster, cvhA encoded a putative sensor histidine kinase with a predicted sensor domain consisting of two trans-membrane segments at the N-terminus and a conserved HATPase_c domain at the C-terminus. The C-terminus polypeptide of CvhA expressed in Escherichia coli was purified and shown to be autophosphorylated with [gamma-32P]ATP in vitro. The phosphoryl group was acid-labile and basic-stable, which supported histidine as the phosphorylation residue. No obvious difference of mycelia development was observed between the null mutant of cvhA generated by targeted gene replacement and the wild-type parental strain 10-22 grown on solid soya flour medium with 2%-8% glucose or sucrose, but the cvhA mutant could form much more abundant aerial mycelia and spores than the wild-type strain on solid soya flour medium supplemented with 6%-8% mannitol, 6%-8% sorbitol, 4%-6% mannose, or 4%-6% fructose. This phenotype was complemented by the cloned wild-type cvhA gene, and no difference was observed for growth curves of the cvhA mutant and the wild strain in liquid minimal medium with the tested sugars at a concentration of 4%, 6% and 8%. We thus propose that CvhA is likely a sensor histidine kinase and negatively regulates the morphological differentiation in a sugar-dependent manner in S. hygroscopicus 10-22.