Hyper-production of butyric acid from delignified rice straw by a novel consolidated bioprocess

A novel consolidated bioprocess for hyper-production of butyric acid from delignified rice straw without exogenous enzymes involved was developed by co-fermentation of Clostridium thermocellum ATCC 27405 and C. thermobutyricum ATCC 49875. Feasibility of the consolidated bioprocess was approved by batch fermentations, with the optimum pH of 6.5. Fed-batch fermentation with a constant pH of 6.5 at 55 °C could enhance the butyric acid yield to a remarkable 33.9 g/L with a selectivity as high as 78%. Metabolic analysis of the co-culture indicated that sugars liberated by C. thermocellum ATCC 27405 were effectively converted to butyric acid by C. thermobutyricum ATCC 49875. Secondary metabolism of C. thermobutyricum ATCC 49875 also contributed to the hyper-production of butyric acid, resulting in the re-assimilation of by-products such as acetic acid and ethanol. This work provides a more effective fermentation process for butyric acid production from lignocellulosic biomass for future applications.