Understanding high ε-poly-L-lysine production by Streptomyces albulus using pH shock strategy in the level of...

ε-Poly-L-lysine (ε-PL) is a natural food preservative, which exhibits antimicrobial activity against a wide spectra of microorganisms. The production of ε-PL was significantly enhanced by pH shock in our previous study, but the underlying mechanism is poorly understood. According to transcriptional and physiological analyses in this study, the mprA/B and pepD signal transduction system was first proved to be presented and activated in Streptomyces albulus M-Z18 by pH shock, which positively regulated the transcription of ε-PL synthetase (Pls) gene and enhanced the Pls activity during fermentation. Furthermore, pH shock changed the ratio of unsaturation to saturation fatty acid in the membrane through up-regulating the transcription of fatty acid desaturase genes (SAZ_RS14940, SAZ_RS14945). In addition, pH shock also enhanced the transcription of cytochrome c oxidase (SAZ_RS15070, SAZ_RS15075), ferredoxin reductase (SAZ_RS34975) and iron sulfur protein (SAZ_RS31410) genes, and finally resulted in the improvement of cell respiratory activity. As a result, pH shock was considered to influence a wide range of proteins including regulators, fatty acid desaturase, respiratory chain component, and ATP-binding cassette transporter during fermentation. These combined influences might contribute to enhanced ε-PL productivity with pH shock.