Investigating the Interaction Between Gluconobacter Oxydans and Bacillus M egaterium for 2-keto-L-gulonic Acid Biosynthesis in the Two-Step Vitamin C Fermentation

In the two-step vitamin C fermentation process, its precursor 2-keto-L-gulonic acid was synthesized from L-sorbose by mixed culture of Gluconobacter oxydans and Bacillus megaterium. The interaction between Gluconobacter oxydans and Bacillus megaterium remains unclear and it is a challenge to mathematically model the mixed growth of these two strains. The Monod-type equations were previously proposed to describe the coupled growth of Gluconobacter oxydans and Bacillus megaterium. However, in this study, we modeled the interaction of these two strains in a macroscopic view by introducing the population theory. Taking account of the fact that the density or concentration of Gluconobacter oxydans or Bacillus megaterium was hardly to measure accurately in the mixed culture broth, the data of concentrations of the substrate and product were used to indirectly investigate the relation between these two strains. Three batch experiments were used to validate our model. And according to the values of identified parameters, the type of interaction between Gluconobacter oxydans and Bacillus megaterium was concluded to be predation, where Gluconobacter oxydans was predator, and Bacillus megaterium was prey.

Construction of synthetic microbial consortia for 2-keto-L-gulonic acid biosynthesis

Currently,the establishment of synthetic microbial consortia with rational strategies has gained extensive attention,becoming one of the important frontiers of synthetic biology.Systems biology can offer insights into the design and construction of synthetic microbial consortia.Taking the high-efficiency production of 2-keto-L-gulonic acid(2-KLG)as an example,we constructed a synthetic microbial consortium“Saccharomyces cerevisiae-Ketogulonigenium vulgare”based on systems biology analysis.In the consortium,K.vulgare was the 2-KLG pro-ducing strain,and S.cerevisiae acted as the helper strain.Comparative transcriptomic analysis was performed on an engineered S.cerevisiae(VTC2)and a wild-type S.cerevisiae BY4741.The results showed that the up-regulated genes in VTC2,compared with BY4741,were mainly involved in glycolysis,TCA cycle,purine metabolism,and biosynthesis of amino acids,B vitamins,and antioxidant proteases,all of which play important roles in pro-moting the growth of K.vulgare.Furthermore,Vitamin C produced by VTC2 could further relieve the oxidative stress in the environment to increase the production of 2-KLG.Therefore,VTC2 would be of great advantage in working with K.vulgare.Thus,the synthetic microbial consortium"VTC2-K.vulgare"was constructed based on transcriptomics analyses,and the accumulation of 2-KLG was increased by 1.49-fold compared with that of mono-cultured K.vulgare,reaching 13.2±0.52 g/L.In addition,the increased production of 2-KLG was accompanied by the up-regulated activities of superoxide dismutase and catalase in the medium and the up-regulated oxidative stress-related genes(sod,cat and gpd)in K.vulgare.The results indicated that the oxida-tive stress in the synthetic microbial consortium was efficiently reduced.Thus,systems analysis confirmed a favorable symbiotic relationship between microorganisms,providing guidance for further engineering synthetic consortia.