Butyric acid as sole product from xylose fermentation by a non-solventogenic Clostridium beijerinckii strain under controlled pH and nutritional conditions

Fermentative processes allow butyric acid to be produced from renewable substrates, which makes this compound commercially attractive. We have employed the non-solventogenic C. beijerinckii strain Br21 to obtain butyric acid from xylose under different nutritional conditions and controlled pH. Reinforced Clostridium Medium (RCM), which has the lowest C/N ratio, provided the highest butyrate/acetate ratio. When the RCM pH was kept at 6.5, butyric acid was the sole product of xylose fermentation by strain Br21. The butyric acid concentration was 5.2 times higher as compared to the fermentation without controlled pH. The genes buk (butyrate kinase) and hyd (hydrogenase) had their expressions enhanced by 6.8 and 2.0 times during the maximal acid production phase. On the other hand, ack (acetate kinase) had its expression weakened by 2.2 times under controlled pH. C. beijerinckii Br21 is a promising strain for highly specific butyric acid production from substrates derived from lignocellulose.