title: Efficient production of ε-poly-L-lysine by Streptomyces ahygroscopicus using one-stage pH control fed-batch fermentation coupled with nutrient feeding.
abstract: ε-Poly-L-lysine (ε-PL) is a homopolymer of L-lysine molecules connected between the ε 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.
authors.affiliation: Guangdong Institute of Microbiology, Ministry-Guangdong Province Jointly State Key Laboratory of Applied Microbiology, Guangzhou 510070, P.R. China.
authors.forename: Sheng-Rong
authors.initials: SR
authors.lastname: Liu
authors.forename: Qing-Ping
authors.initials: QP
authors.lastname: Wu
authors.forename: Ju-Mei
authors.initials: JM
authors.lastname: Zhang
authors.forename: Shu-Ping
authors.initials: SP
authors.lastname: Mo
mesh_terms: D061249:Batch Cell Culture Techniques; D018533:Biomass; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D009584:Nitrogen / Q000378:metabolism; D011107:Polylysine / Q000096:biosynthesis*; D013302:Streptomyces / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D011107:Polylysine; D009584:Nitrogen