Metabolomic analysis of the positive effects on Ketogulonigenium vulgare growth and 2-keto-L-gulonic acid production by reduced glutathione.

Ketogulonigenium vulgare has long been used in industry to produce 2-keto-L-gulonic acid (2KGA), the precursor of vitamin C. This fermentation process involves co-culture of K. vulgare and a Bacillus species. Early studies demonstrated that the presence of the Bacillus strain can enhance the cellular growth and 2KGA production of K. vulgare. However, the molecular mechanism behind how Bacillus affects the growth of K. vulgare and 2KGA production remains unclear. In addition, the inclusion of Bacillus in the fermentation process presents difficulties for the post-separation and purification of 2KGA. To address these issues, efforts have been made to replace the Bacillus strain with chemical compounds. In this study, we found that adding thiol compounds such as reduced glutathione (GSH) and dithiothreitol (DTT) to the K. vulgare mono-culture system can increase the growth of K. vulgare about twofold, and increase 2KGA production by about fivefold. The effects of thiols on the concentrations of some cellular metabolites were determined using gas chromatography coupled to time-of-flight mass spectrometry. The results showed that the levels of intracellular amino acids and intermediates in the pentose phosphate pathway increased significantly after thiol addition. Interestingly, when GSH was added, the levels of key intracellular metabolites in primary metabolic pathways and the cell biomass both reached their maximum in the first 36 h, and then decreased when the thiol was exhausted. These findings indicate that cell growth needs the assistance of a high concentration of thiols. This study is the first report that chemically defined compounds were used to enhance the growth of K. vulgare and 2KGA production. Furthermore, it also provides new insights into the possible cellular interaction between Bacillus species and K. vulgare.