Identification of genetic variations associated with epsilon-poly-lysine biosynthesis in Streptomyces albulus ZPM by genome sequencing

The biosynthesis of the antibiotic epsilon-poly-lysine (ɛ-PL) in Streptomyces albulus is performed by polylysine synthase (pls); however, the regulatory mechanism of this process is still unknown. Here, we first obtained the complete genome sequence of S. albulus ZPM, which consists of 9,784,577 bp and has a GC content of 72.2%. The genome houses 44 gene clusters for secondary metabolite biosynthesis, in which 20 gene clusters are involved in the biosynthesis of polyketides and nonribosomally synthesized peptides. High-throughput sequencing was further performed, and genetic variants were identified from pooled libraries consisting of the 30 highest-yield mutants or 30 lowest-yield mutants. More than 350 genetic variants associated with ɛ-PL yield have been identified. One hundred sixty-two affected proteins, from important metabolic enzymes to novel transcriptional regulators, were identified as being related to ɛ-PL synthesis. HrdD, one of the affected genes, is a sigma factor that shows the most sensitive response to pH change and contains a non-synonymous mutation (A132V) in mutant strains with lower ɛ-PL yields. Electrophoretic mobility shift assays showed that the pls gene is likely regulated by transcriptional activator HrdD. The data obtained in this study will facilitate future studies on ɛ-PL yield improvement and industrial bioprocess optimization.