Investigation on the effects of ϵ-poly-L-lysine on a producing strain Streptomyces ahygroscopicus GIM8, for better understanding its biosynthesis

Recent advances in microbial ε-poly-L-lysine fermentation and its diverse applications

The naturally occurring homo-polyamide biopolymer, ε-poly-L-lysine (ε-PL) consists of 25-35 L-lysine residues with amide linkages between α-carboxyl groups and ε-amino groups. ɛ-PL exhibits several useful properties because of its unusual structure, such as biodegradability, water solubility, no human toxicity, and broad-spectrum antibacterial activities; it is widely applied in the fields of food, medicine, clinical chemistry and electronics. However, current industrial production of ε-PL is only performed in a few countries. Based on an analysis of the physiological characteristics of ε-PL fermentation, current advances that enhance ε-PL fermentation, from strain improvement to product isolation are systematically reviewed, focusing on: (1) elucidating the metabolic pathway and regulatory mechanism of ε-PL synthesis; (2) enhancing biosynthetic performance through mutagenesis, fermentation optimization and metabolic engineering; and (3) understanding and improving the biological activity and functional properties of ε-PL. Finally, perspectives on engineering and exploiting ε-PL as a source material for the production of various advanced materials are also discussed, providing scientific guidelines for researchers to further improve the ε-PL fermentation process.

Cysteine synthase A overexpression in Corynebacterium glutamicum enhances l-isoleucine production

Cysteine synthase A (CysK) catalyzes the last reaction of l-cysteine synthesis in bacteria, but its moonlighting functions have been revealed recently. In this study, CysK was overexpressed in Corynebacterium glutamicum IWJ001, an l-isoleucine producer. Compared with the control IWJ001/pDXW-8, IWJ001/pDXW-8-cysK cells grew fast during log phase, and produced 26.5% more l-isoleucine in flask fermentation and 23.5% more l-isoleucine in fed-batch fermentation. The key genes aspC, lysC, hom, thrB, ilvA, and ilvBN involved in l-isoleucine biosynthesis were all upregulated in IWJ001/pDXW-8-cysK, compared with IWJ001/pDXW-8. In addition, IWJ001/pDXW-8-cysK cells were longer and thicker than IWJ001/pDXW-8 cells. Compared with IWJ001/pDXW-8, the membrane permeability increased 15.8% and biofilm formation ability decreased 71.3% for IWJ001/pDXW-8-cysK cells. The results demonstrate that CysK overexpression in C. glutamicum is a good approach to enhance l-isoleucine production.