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

Mandlaa Mandlaa,Hui Xu,Xiaodong Han,Ziyu Sun,Ruigang Wang,Weichao Yang

doi:10.1186/s13568-018-0562-y

Mandlaa Mandlaa, Hui Xu + Show 4 more

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https://doi.org/10.1186/s13568-018-0562-y

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Abstract

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.

Highlights

2-Keto-l-gulonic acid is bio-converted from l-sorbose by mixed fermentation of Ketogulonicigenium vulgare and a helper strain
The results indicated the co-culture system composed by Bc 21 and K. vulgare 418 had better stability and adaptability whether in low (8%) or high (14%) concentration of l-sorbose
The inhibition effect of l-sorbose on the growth of helper strain makes assurance of the balanced proportion of helper strain and K. vulgare and an effective production of 2-Keto-l-gulonic acid (2-KLG) in low concentration of l-sorbose fermentation, the inhibition effect has greatly influenced the growth of the helper strain and led a low 2-KLG production in high concentration of l-sorbose fermentation

Summary

Introduction

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. 2-Keto-l-gulonic acid (2-KLG) is a precursor of vitamin C (Bremus et al 2006), and it is mainly bio-converted from l-sorbose via a co-culture system in two-step fermentation process of vitamin C (Pappenberger and Hohmann 2014). This co-culture system is composed by two strains: Ketogulonicigenium vulgare (previously identified as Gluconobacter oxydans) (Urbance et al 2001; Yin et al 1980) and the helper strain (mostly belongs to Bacillus spp.) (Bremus et al 2006). These results helped us obtain effective LHS and improve the 2-KLG production under high concentration of l-sorbose

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