Functional expression of SCO7832 stimulates tautomycetin production via pathway-specific regulatory gene overexpression in Streptomyces sp. CK4412.

Comparative transcriptome analysis has revealed several acidic pH shock-induced genes presumably involved with stimulation of antibiotic production by S. coelicolor (Kim et al. Appl Microbiol Biotechnol 2007). Streptomyces sp. CK4412 produces a novel T cell-specific immunosuppressive compound, tautomycetin (TMC). When cultured at acidic pH medium, it also exhibited higher TMC productivity. To verify a gene responsible for acidic pH shock-induced TMC stimulation, a putative acid-shock-induced gene, SCO7832 encoding an Na(+)/H(+) antiporter protein, was cloned under the influence of a strong constitutive ermE* promoter in an integrative expression pSET152 vector. This was followed by its conjugation into the TMC-producing Streptomyces sp. CK4412. Comparing TMC production and antifungal activity of wild-type and the SCO7832-containing exconjugant revealed that SCO7832 stimulated TMC production more than 3.5-fold in Streptomyces sp. CK4412. The over-expression of SCO7832 did not affect the ratio between intra- and extra-cellular TMC productions. However, it significantly stimulated the expression of a TMC-specific positive regulatory gene. This implies that the stimulatory effect of SCO7832 functions in TMC-producing Streptomyces sp. CK4412 via up-regulation of a TMC pathway-specific positive regulatory gene, tmcN overexpression.