(554d) Acetic Acid Production from Glucose and Formate By the Co-Culture of Clostridium Formicoaceticum and Lactobacillus Lactis

Clostridium formicoaceticum, is a mixotrophic bacteria that produce acetic acid from different carbon sources such as glycerol, lactic acid, formic acid, fructose, and carbon dioxide. Lactobacillus lactis is a facultatively anaerobic, gram-positive bacteria that convert glucose to lactic acid. At initial, mixotrophic fermentation with C. formicoaceticum was assessed to identify the best possible lactate and format concentrations and their molar ratios to maximize the carbon conversion and acetate titer. The media with different concentrations of format and lactate and with different molar ratios of them screened in a serum bottle to identify the growth of bacteria and production of acetate. The target was to achieve the production of acetate at a high yield of >0.9 g/g substrate (lactate and Format) under anaerobic conditions at 37˚C. The outcome of 0.91 g/g acetate is obtained from the culture with 2 g/L of formic acid and 5 g/L of lactic acid in combination. This was used to guide in the design and optimization of cocultured fermentation of C. formicoaceticum and L. lactis.

Further, the coculture fermentation of L. lactis and C. formicoaceticum was done to evaluate the interaction between them under various culture conditions such as pH, substrate concentration, nutrition level, etc. initially with wild type strain and then with the engineered L. lactis that has increased lactate production. Substrate (glucose and formate) consumption, production (acetate) production, and cell density of each strain were monitored throughout the culture period. Additionally, a reporter gene, mCherry, was loaded into L. lactis to enable the quantification of cell population ratio. The interactions between L. lactis and C. formicoaceticum and their effects on community (commensal and symbiotic) growth under optimized conditions were studied and found to enhance acetate production from glucose and formate at a high yield of >0.9 g/g substrate. This result has also guided us in the design and optimization of the consortia fermentation for butanol production.