Kinetics of Homoacetic Fermentation of Lactate by Clostridium formicoaceticum

Clostridium formicoaceticum homofermentatively converted lactate to acetate at mesophilic temperatures (30 to 42 degrees C) and at pHs between 6.6 and 9.6. The production of acetate was found to be growth associated. Approximately 0.96 g of acetic acid and 0.066 g of cells were formed from each gram of lactic acid consumed at 37 degrees C. The concentration of the substrate (lactate) had little or no effect on the growth rate; however, the fermentation was inhibited by acetic acid. The bacterium grew at an optimal pH of 7.6 and an optimal temperature of 37 degrees C. Small amounts of bicarbonate were stimulatory to bacterial growth. Bacterial growth was enhanced, however, by the use of higher concentrations of bicarbonate in the media, only because higher buffer capacities were obtained and proper medium pH could be maintained for growth. Based on its ability to convert lactate to acetate, this homoacetic bacterium may be important in the anaerobic methanogenic process when lactate is a major intermediary metabolite.