Fermentation of sweet sorghum derived sugars to butyric acid at high titer and productivity by a thermophile Clostridium thermobutyricum at 50°C

Butyric acid is a commodity chemical produced at industrial scale by chemical synthesis and by fermentation. Butyric acid is used as a feedstock for synthesis of plastics, plasticizers and surfactants Production of butyrate from renewable biological feedstocks rather than from petroleum has the additional benefit of supporting rural economies. In this study, a moderate thermophile Clostridium thermobutyricum is shown to ferment the sugars in sweet sorghum juice at 50°C to 44 g.L^-1 butyrate at a calculated highest volumetric productivity of 1.45 g.L^-1.h^-1 (molar butyrate yield of 0.85 based on sugars fermented). This volumetric productivity is among the highest reported for batch fermentations. Sugars from acid and enzyme-treated sweet sorghum bagasse were also fermented to butyrate by this organism with a molar yield of 0.81 (based on the amount of cellulose and hemicellulose). By combining the results from juice and bagasse, the calculated yield of butyric acid is approximately 90 kg per tonne of fresh sweet sorghum stalk. And this compares favorably to our previous reported theoretical yield of 97 kg of ethanol per tonne of sweet sorghum. Thus this study demonstrates that C. thermobutyricum can be an effective microbial biocatalyst for production of bio-based butyrate from renewable feedstocks at 50°C.