Abstract: This study compared the differences in the growth and metabolism of Clostridium celerecrescens JSJ-1, a strain able to produce caproic acid, and Clostridium tyrobutyricum D-1, a stain able to produce butyric acid, when cultured separately or co-cultured in different systems (solid medium, and liquid medium with or without use of dialysis bag). Furthermore, this study investigated the effect and mechanism of co-culture with C. tyrobutyricum on caproic acid metabolism in caproic acid-producing bacteria by culturing JSJ-1 alone in the presence of butyric acid or sodium butyrate at different concentrations. The results showed that when co-cultured on a composite solid medium containing glucose in anaerobic conditions at 34 ℃, D-1 grew better than JSJ-1, and could preferentially utilize glucose for growth. The generation time of caproic acid was three days earlier when D-1 and JSJ-1 were co-cultured in a liquid medium than when JSJ-1 was cultured alone under the same conditions, and the concentration of caproic acid was 9.93 and 9.79 g/L on the 12th day in the two cases, respectively. Glucose had a strong inhibitory effect on the production of caproic acid by JSJ-1, which could be relieved by preferential utilization of by D-1 upon co-culture. The co-culture in the liquid medium with and without use of dialysis bag were compared, revealing that whether there was direct contact between JSJ-1 and D-1 had no effect on the yield of caproic acid. By purely culturing JSJ-1 in the presence of butyric acid or sodium butyrate, it was found that butyric acid generated by D-1 at pH 6–6.5 could promote the synthesis of caproic acid by JSJ-1. During co-culture, the preferential utilization of glucose by D-1 could relieve the inhibitory effect of glucose on the production of caproic acid, and butyric acid produced by D-1 could promote the synthesis of caproic acid.

Key words: Clostridium celerecrescens; Clostridium tyrobutyricum; pure culture; co-culture