Metabolic flux analysis of coenzyme Q₁₀ synthesized by Rhodobacter sphaeroides under the influence of different pH...

Coenzyme Q₁₀ (CoQ₁₀) is crucial for human beings, especially in the fields of biology and medicine. The aim of this experiment was to investigate the conditions for increasing CoQ₁₀ production. At present, microbial fermentation is the main production method of CoQ₁₀, and the production process of microbial CoQ₁₀ metabolism control fermentation is very critical. Metabolic flux is one of the most important determinants of cell physiology in metabolic engineering. Metabolic flux analysis (MFA) is used to estimate the intracellular flux in metabolic networks. In this experiment, Rhodobacter sphaeroides was used as the research object to analyze the effects of aqueous ammonia (NH₃·H₂O) and calcium carbonate (CaCO₃) on the metabolic flux of CoQ₁₀. When CaCO₃ was used to adjust the pH, the yield of CoQ₁₀ was 274.43 mg·L^-1 (8.71 mg·g^-1 DCW), which was higher than that of NH₃·H₂O adjustment. The results indicated that when CaCO₃ was used to adjust pH, more glucose-6-phosphate (G6P) entered the pentose phosphate (HMP) pathway and produced more NADPH, which enhanced the synthesis of CoQ₁₀. At the chorismic acid node, more metabolic fluxes were involved in the synthesis of p-hydroxybenzoic acid (pHBA; the synthetic precursor of CoQ₁₀), enhancing the anabolic flow of CoQ₁₀. In addition, Ca²⁺ produced by the reaction of CaCO₃ with organic acids promotes the synthesis of CoQ₁₀. In summary, the use of CaCO₃ adjustment is more favorable for the synthesis of CoQ₁₀ by R. sphaeroides than NH₃·H₂O adjustment. The migration of metabolic flux caused by the perturbation of culture conditions was analyzed to compare the changes in the distribution of intracellular metabolic fluxes for the synthesis of CoQ₁₀. Thus, the main nodes of the metabolic network were identified as G6P and chorismic acid. This provides a theoretical basis for the modification of genes related to the CoQ₁₀ synthesis pathway.