cvhA Gene of Streptomyces hygroscopicus 10–22 Encodes a Negative Regulator for Mycelia Development

Abstract 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 [γ‐ 32 P]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 pheno‐type 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. Edited by
 Marchler BALLER