Enhancing ε-poly-L-lysine production in Streptomyces albulus through L-lysine importer engineering.

ε-Poly-L-lysine (ε-PL) is a homopolymer of L-lysine residues produced by microorganisms, widely utilized in the food, pharmaceutical, and cosmetic industries. However, the development of efficient microbial cell factories (MCFs) for ε-PL production remains challenging. In this study, L-lysine importers were systematically screened, identified, and engineered to enhance ε-PL biosynthesis. First, an ε-PL-producing strain, Streptomyces albulus GS114, efficiently utilizing exogenous L-lysine, was selected. Bioinformatics analysis identified seven putative L-lysine importers in GS114, among which GL6157 was confirmed as the primary importer through molecular docking, transcriptional analysis, and genetic manipulation. Through combinatorial optimization of GL6157 expression coupled with overexpression of ε-poly-L-lysine synthase (pls), we engineered the GS114/pls-GL6157 strain, which achieved a ε-PL of 94.0 g/L in fed-batch fermentation. To our knowledge, this represents the highest reported yield to date. These findings demonstrate that transporter engineering is an effective strategy for enhancing ε-PL biosynthesis in industrial MCFs.