Abstract: To study the effect of co-culture with Saccharomyces cerevisiae on the metabolism of caproic acid-producing bacteria and its mechanism, a strain of Clostridium celerecrescens JSJ-1 that can produce caproic acid and S. cerevisiae C-1 were cultured separately or co-cultured under different nutrient conditions. We compared the growth and metabolism (number of microbial colonies, glucose, ethanol, butyric acid, caproic acid) of the two strains in monoculture and co-culture. The results showed that S. cerevisiae C-1 grew better than C. celerecrescens JSJ-1 under anaerobic static culture conditions at 34 ℃, and could preferentially utilize glucose in the medium. When glucose was used as the sole carbon source, S. cerevisiae C-1 could utilize glucose to produce ethanol as a substrate for the synthesis of caproic acid by C. celerecrescens JSJ-1. When the medium contained 0.5% glucose and 2% ethanol, the co-culture produced caproic acid four days earlier than C. celerecrescens JSJ-1 alone. Glucose had a strong inhibitory effect on the production of caproic acid by C. celerecrescens JSJ-1. S. cerevisiae C-1 could utilize glucose to relieve its inhibitory effect on the production of caproic acid upon co-culture. During the fermentation of nongxiangxing baijiu, S. cerevisiae can not only provide substrates for caproic acid-producing bacteria to synthesize caproic acid, but also alleviate the inhibitory effect of glucose on caproic acid production.

Key words: Clostridium celerecrescens; Saccharomyces cerevisiae; pure culture; co-culture; caproic acid; microbial interaction