Enhanced 2-keto- l-gulonic acid production by applying l-sorbose-tolerant helper strain in the co-culture system

摘要

2-Keto- l -gulonic acid (the precursor of vitamin C) is bio-converted from l -sorbose by mixed fermentation of Ketogulonicigenium vulgare and a helper strain. The helper strain promotes the conversion of 2-KLG by enhancing the growth of K. vulgare , but its growth is greatly inhibited by high concentration of l -sorbose, which consequently influence the 2-KLG production. The aim of this study is to obtain l -sorbose-tolerant helper strain (LHS) by experimental evolution for reduced l -sorbose-inhibition-effect and enhanced 2-KLG productivity in high concentration of l -sorbose. After three steps screening by using our devised screening strategy, three strains (i.e., Bc 21, Bc 47, Bc 50) with high resistance to high concentration of l -sorbose were obtained. The fermentation tests by co-culturing Bc 21 and K. vulgare 418 showed that the production of 2-KLG was increased by 17.9% in 11% l -sorbose medium than that in 8% after 55?h of fermentation and the conversion rate was 89.5%. The results suggested that Bc 21 could be an ideal helper strain for 2-KLG production under high concentration of l -sorbose and demonstrated the feasibility of using experimental evolution to breed LHS for vitamin C production.