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.