Efficient production of ε-poly-l-lysine from agro-industrial by-products by Streptomyces sp. M-Z18

Abstract

e-Poly-l-lysine (e-PL)—a natural food preservative with wide antimicrobial activity and high food safety—is increasingly attracting widespread attention. However, the high cost of raw materials severely impairs its economy and utilization. In this study, agro-industrial by-products, i.e., fish meal coupled with corn steep liquor, were employed as alternative organic nitrogen sources for industrial e-PL production by Streptomyces sp. M-Z18. An economical medium was then developed by using an artificial neural network. Amino acids analyses showed that the improved medium was rich in glutamate, arginine, lysine and aspartate, which not only elevated the acid tolerance capability of the mycelia but also enhanced cell growth and e-PL production. Subsequently, a cost-effective and efficient strategy for e-PL production was established on fermenter scale, based on the improved medium and two-stage pH control. Notably, e-PL production and productivity reached 35.24 g/L and 4.85 g/L day in fed-batch fermentation. Further profit assessment at the 10 m3 scale indicated that application of this strategy resulted in a net profit increase of 9,057 USD. Therefore, the proposed strategy has great potential for industrial production of e-PL.