Heterologous Expression and Adaptive Evolution of ε-Poly-lysine Synthase Gene in Corynebacterium glutamicum

ε-Poly-L-lysine (ε-PL) is a natural preservative that has excellent properties such as high safety, good antibacterial effect, wide antibacterial spectrum, and high temperature resistance compared to other food preservatives. At present, the main production strain of ε-PL is Streptomyces albulus (S. albulus). Due to the large amount of mycelium and by-products during fermentation, its production cost is much higher than other food preservatives, which seriously hinders the application of ε-PL in the food industry. Corynebacterium glutamicum (C. glutamicum) is a food safety strain that is widely used in the fermentation industry to produce various amino acids. Its ability to produce high amounts of L-lysine can provide sufficient precursor substances for the synthesis of ε-PL, making it an ideal strain for the heterologous expression of ε-PL synthase genes (pls). In this experiment, a recombinant C. glutamicum capable of synthesizing ε-PL and exhibiting certain physiological resistance to ε-PL was obtained by amplifying pls and heterologous expression in C. glutamicum for the first time. Further optimization of the fermentation temperature, initial pH, and inoculation amount of the recombinant strain resulted in an increase in the ε-PL fermentation yield from 0.12 g/L to 0.22 g/L. Finally, through adaptive evolution of the recombinant strain, the ε-PL tolerance of the recombinant strain was increased to 1.3 g/L, and the yield of ε-PL ultimately reached 0.34 g/L, which increased by 54.55% compared to the initial strain. The recombinant C. glutamicum constructed in this study can significantly shorten the fermentation cycle, reduce bacterial volume and the synthesis of secondary metabolites, which is beneficial for the separation and purification of products, thereby further reducing the production cost of ε-PL and accelerating the process of replacing chemical food preservatives with natural food preservatives.