Salt-induced 7-deoxypactamycin and oligomycin production in Streptomyces sp. strain TUA-HK1GM isolated from kusaya gravy

Streptomyces produce various antibiotics and bioactive compounds as secondary metabolites. Although they are normally found in soil, strains of Streptomyces have also been discovered in non-soil environments, including marine habitats. These non-terrestrial strains may have specific metabolic features compared with those of soil-dwelling Streptomyces. In this study, we investigated phenotypic and taxonomic characteristics, and antibiotic production of a Streptomyces sp. strain TUA-HK1GM that we previously isolated from kusaya gravy, a fermented fish gravy high in salt content. Microbiological analysis revealed distinct properties compared to closely related species, particularly in its ability to grow at 7% NaCl. Phylogenetic analysis suggested that strain TUA-HK1GM is a novel actinomycete species. We investigated the effects of NaCl supplementation on secondary metabolite biosynthesis, with a focus on antibiotic production. This strain produced antifungal compounds in the absence of NaCl, and these compounds were identified as oligomycins A and B. On the other hand, a large amount of anti-Staphylococcus compound was produced alongside oligomycin in the presence of NaCl. This compound had m/z values of 543.2813 [M + H]⁺ and 565.2633 [M+Na]⁺, which were consistent with those of 7-deoxypactamycin. Enhancement (32-fold) of oligomycin A production was also observed in a manner dependent on the duration of NaCl exposure. Supplementation with NaCl during cultivation demonstrated that prolonged exposure to NaCl increased the antibiotic production. These results indicate that the novel strain TUA-HK1GM has a characteristic mechanism that involves secondary metabolic activation by NaCl.