Production of butyric acid by a cellulolytic actinobacterium Thermobifida fusca on cellulose

•T. fusca was found to produce butyric acid directly from lignocellulosic biomass.•The best the yield of butyric acid was 0.52 g/g C.•The maximum titer of 2.1 g/L butyric acid was achieved on 9.66 g/L of cellulose.•There was 2.37 g/L butyric acid produced under optimal conditions.•The pathway of producing butyric acid was identified experimentally.

Thermobifida fusca not only produces cellulases, hemicellulases and xylanases, but also excretes butyric acid. In order to achieve a high yield of butyric acid, the effect of different carbon sources: mannose, xylose, lactose, cellobiose, glucose, sucrose and acetates, on butyric acid production was studied. The highest yield of butyric acid was 0.67 g/g C (g-butyric acid/g-carbon input) on cellobiose. The best stir speed and aeration rate for butyric acid production were found to be 400 rpm and 2 vvm in a 5-L fermentor. The maximum titer of 2.1 g/L butyric acid was achieved on 9.66 g/L cellulose. In order to test the production of butyric acid on lignocellulosic biomass, corn stover was used as the substrate, on which there was 2.37 g/L butyric acid produced under the optimized conditions. In addition, butyric acid synthesis pathway was identified involving five genes that catalyzed reactions from acetyl-CoA to butanoyl-CoA in T. fusca.