Analysis and validation of the pho regulon in the tacrolimus-producer strain Streptomyces tsukubaensis: differences with the model organism Streptomyces coelicolor.

Inorganic and organic phosphate controls both primary and secondary metabolism in Streptomyces genus. Metabolism regulation by phosphate in Streptomyces species is mediated by the PhoR-PhoP two-component system. Response regulator PhoP binds to conserved sequences of 11 nucleotides called direct repeat units (DRus), whose organization and conservation determine the binding of PhoP to distinct promoters. Streptomyces tsukubaensis is the industrial producer of the clinical immunosuppressant tacrolimus (FK506). A bioinformatic genome analysis detected several genes with conserved PHO boxes involved in phosphate scavenging and transport, nitrogen regulation, and secondary metabolite production. In this article, the PhoP regulation has been confirmed by electrophoretic mobility shift assays (EMSA) of the most relevant members of the traditional pho regulon such as the two-component system PhoR-P or genes involved in high-affinity phosphate transport (pstSCAB) and low-affinity phosphate transport (pit). However, the PhoP control over phosphatase genes in S. tsukubaensis is significantly different from the pattern reported in the model bacteria Streptomyces coelicolor. Thus, neither the alkaline phosphatase PhoA nor PhoD is regulated by PhoP. On the contrary, the binding of PhoP to the promoter of a novel putative phosphatase PhoX was confirmed. A crosstalk of the PhoP and GlnR regulators, which balances phosphate and nitrogen utilization, also occurs in S. tsukubaensis but slightly modified. Finally, PhoP regulates genes, like afsS, that link phosphate control and secondary metabolite production in S. tsukubaensis. In summary, there are notable differences between the regulation of specific genes of the pho regulon in S. tsukubaensis and the model organism S. coelicolor.