Activation of a Silent Type II PKS Pathway in Streptomyces avermitilis via a Reintroduction Strategy

Genome mining of the industrially important bacterium Streptomyces avermitilis was performed via antiSMASH prediction and Protein BLAST analysis, which uncovered a previously uncharacterized cryptic type II polyketide synthase (PKS) biosynthetic gene cluster (BGC) designated spy. To activate this silent biosynthetic pathway in its native genomic background, we employed a gene cluster reintroduction strategy in which the spy cluster was captured and reintroduced into the optimized chassis strain S. avermitilis SUKA17. This approach successfully activated the silent pathway, leading to the isolation and characterization of six new griseusin analogues, spiromycins A-F (1-6), together with two anthraquinone derivatives, spoanthraquinones A (7) and B (8). Bioactivity evaluation revealed that spiromycins A-F exhibit potent antibacterial activities, with MIC values as low as 0.5 μM, whereas spoanthraquinones A (7) and B (8) display significant antioxidant activity in a DPPH· radical scavenging assay, with IC₅₀ values of 27.23 ± 1.69 μM and 61.65 ± 1.37 μM, respectively. Overall, this work validates that reintroduction of endogenous BGCs represents a robust genome mining approach to activate silent metabolic pathways and accelerate the discovery of bioactive novel natural products.