Abstract
BackgroundIn the industry, the conventional two-step fermentation method was used to produce 2-keto-l-gulonic acid (2-KGA), the precursor of vitamin C, by three strains, namely, Gluconobacter oxydans, Bacillus spp. and Ketogulonicigenium vulgare. Despite its high production efficiency, the long incubation period and an additional second sterilization process inhibit the further development. Therefore, we aimed to reorganize a synthetic consortium of G. oxydans and K. vulgare for one-step fermentation of 2-KGA and enhance the symbiotic interaction between microorganisms to perform better.ResultsDuring the fermentation, competition for sorbose of G. oxydans arose when co-cultured with K. vulgare. In this study, the competition between the two microbes was alleviated and their mutualism was enhanced by deleting genes involved in sorbose metabolism of G. oxydans. In the engineered synthetic consortium (H6 + Kv), the yield of 2-KGA (mol/mol) against d-sorbitol reached 89.7 % within 36 h, increased by 29.6 %. Furthermore, metabolomic analysis was used to verify the enhancement of the symbiotic relationship and to provide us potential strategies for improving the synthetic consortium. Additionally, a significant redistribution of metabolism occurred by co-culturing the K. vulgare with the engineered G. oxydans, mainly reflected in the increased TCA cycle, purine, and fatty acid metabolism.ConclusionsWe reorganized and optimized a synthetic consortium of G. oxydans and K. vulgare to produce 2-KGA directly from d-sorbitol. The yield of 2-KGA was comparable to that of the conventional two-step fermentation. The metabolic interaction between the strains was further investigated by metabolomics, which verified the enhancement of the mutualism between the microbes and gave us a better understanding of the synthetic consortium.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0418-6) contains supplementary material, which is available to authorized users.
Highlights
In the industry, the conventional two-step fermentation method was used to produce 2-keto-l-gulonic acid (2-KGA), the precursor of vitamin C, by three strains, namely, Gluconobacter oxydans, Bacillus spp. and Ketogulonicigenium vulgare
Reorganization of a synthetic microbial consortium for one‐step vitamin C fermentation Because of the survival traits of K. vulgare, the companion bacterium is not confined to Bacillus spp., some other bacteria, such as Xanthomonas maltophilia [22], can be a good partner
Whereas in the control experiment in which only K. vulgare (Fig. 1d) or G. oxydans was cultured, no 2-KGA was produced. These results showed that l-sorbose produced by G. oxydans diffused into K. vulgare cells and was subsequently oxidized
Summary
The conventional two-step fermentation method was used to produce 2-keto-l-gulonic acid (2-KGA), the precursor of vitamin C, by three strains, namely, Gluconobacter oxydans, Bacillus spp. and Ketogulonicigenium vulgare. Omics study can provide deep insights into the mechanism of metabolic crosstalk in a consortium at the global level and indicate the way to better understand the relationship between the species [11] Researchers have adopted this approach to investigate the co-cultured microbial systems, including some previous studies about the metabolic cooperation of Bacillus megaterium and Ketogulonicigenium vulgare in two-step vitamin C fermentation [12,13,14,15,16]. Metabolomic analysis was used to better understand the specialization and cooperation between Gluconobacter oxydans and K. vulgare in the reorganized microbial consortium These analyses verified the alleviation of competition and the enhancement of the symbiotic relationship, which provided us potential strategies for further construction of the microbes
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