Functional analysis of a BarX homologue (SngA) as a pleiotropic regulator in Streptomyces natalensis

The prior sequencing of the upstream region of the gamma-butyrolactone autoregulator receptor gene (sngR) in Streptomyces natalensis revealed the presence of a 972-bp gene encoding a BarX homologue (SngA), which acts as a pleiotropic regulator controlling secondary metabolism and morphological differentiation. In this study, we investigated the in vivo function of SngA in S. natalensis, by comparing the natamycin production, morphology, and transcription of genes related to natamycin biosynthesis in a wild-type strain and a sngA-deleted mutant. The disruption of sngA resulted in a decrease in natamycin production, and in the induction of pigment production that had not been previously observed from S. natalensis. On the other hand, the insertion of the intact sngA with its own promoter, into the wild-type strain, resulted in a 1.7-fold increase in natamycin production. Spore formation decreased in comparison to that of the wild-type strain when the sngA-deleted mutant was grown on YEME agar, MS medium, and ISP4 medium. All phenotypes were restored to the original wild-type phenotypes upon complementation with the intact sngA, suggesting that SngA has pleiotropic functions in controlling both morphological differentiation and secondary metabolite production.