Efficient Production of ε-Poly-L-Lysine by Streptomyces ahygroscopicus Using One-Stage pH Control Fed-Batch Fermentation Coupled with Nutrient Feeding

• Published in: Journal of microbiology and biotechnology Vol. 25; no. 3; pp. 358 - 365
• Main Authors: Liu, Sheng-Rong, Wu, Qing-Ping, Zhang, Ju-Mei, Mo, Shu-Ping
• Format: Journal Article
• Language: Korean
• Published: 한국미생물생명공학회 31.03.2015
• Subjects: fed-batch fermentation; nutrient feeding; one-stage pH control; Streptomyces; ε-poly-L-Lysine; Streptomyces; ε-poly-L-lysine; one-stage pH control; nutrient feeding; fed-batch fermentation
• ISSN: 1017-7825; 1738-8872

ε-Poly-L-lysine (ε-PL) is a homopolymer of L-lysine molecules connected between the epsilon amino and alpha carboxyl groups. This polymer is currently used as a natural preservative in food. Insufficient biomass is a major problem in ε-PL fermentation. Here, to improve cell growth and ε-PL productivity, various nitrogen-rich nutrients were supplemented into flask cultures after 16 h cultivation, marking the onset of ε-PL biosynthesis. Yeast extract, soybean powder, corn powder, and beef extract significantly improved cell growth. In terms of ε-PL productivity, yeast extract at 0.5% (w/v) gave the maximum yield (2.24 g/l), 115.4% higher than the control (1.04 g/l), followed by soybean powder (1.86 g/l) at 1% (w/v) and corn powder (1.72 g/l) at 1% (w/v). However, supplementation with beef extract inhibited ε-PL production. The optimal time for supplementation for all nutrients examined was at 16 h cultivation. The kinetics of yeast-extract-supplemented cultures showed enhanced cell growth and production duration. Thus, the most commonly used two-stage pH control fed-batch fermentation method was modified by omitting the pH 5.0-controlled period, and coupling the procedure with nutrient feeding in the pH 3.9-controlled phase. Using this process, by continuously feeding 0.5 g/h of yeast extract, soybean powder, or corn powder into cultures in a 30 L fermenter, the final ε-PL titer reached 28.2 g/l, 23.7 g/l, and 21.4 g/l, respectively, 91.8%, 61.2%, and 45.6% higher than that of the control (14.7 g/l). This describes a promising option for the mass production of ε-PL.