Biosynthetic Baeyer–Villiger Chemistry Enables Access to Two Anthracene Scaffolds from a Single Gene Cluster in Deep-Sea-Derived Streptomyces olivaceus SCSIO T05

Four known compounds, rishirilide B ( 1 ), rishirilide C ( 2 ), lupinacidin A ( 3 ), and galvaquinone B ( 4 ), representing two anthracene scaffolds typical of aromatic polyketides, were isolated from a culture of the deep-sea-derived Streptomyces olivaceus SCSIO T05. From the S. olivaceus producer was cloned and sequenced the rsd biosynthetic gene cluster (BGC) that drives rishirilide biosynthesis. The structural gene rsdK 2 inactivation and heterologous expression of the rsd BGC confirmed the single rsd BGC encodes construction of 1 – 4 and, thus, accounts for two anthracene scaffolds. Precursor incubation experiments with 13 C-labeled acetate revealed that a Baeyer–Villiger-type rearrangement plays a central role in construction of 1 – 4 . Two luciferase monooxygenase components, along with a reductase component, are presumably involved in the Baeyer–Villiger-type rearrangement reaction enabling access to the two anthracene scaffold variants. Engineering of the rsd BGC unveiled three SARP family transcriptional regulators, enhancing anthracene production. Inactivation of rsdR 4, a MarR family transcriptional regulator, failed to impact production of 1 – 4, although production of 3 was slightly improved; most importantly rsdR 4 inactivation led to the new adduct 6 in high titer. Notably, inactivation of rsdH, a putative amidohydrolase, substantially improved the overall titers of 1 – 4 by more than 4-fold.