Characterization of Several Clostridia for Production of Ethanol and Volatile Fatty Acids from Plant-based Substrates

The products of four species of Clostridium were characterized in order to explore potential for biofuel and biochemical production in a consolidated bioprocessing (CBP) system. C. phytofermentans, C. cellulolyticum, C. cellulovorans, and C. thermocellum were grown on several plant-based substrates. These six substrates were tested for ethanol and co-product yields: cellobiose, crystalline cellulose, fibrous cellulose, xylan, crystalline cellulose + xylan, fibrous cellulose + xylan. Cellobiose was found to be the highest ethanol yielding substrate, and among the four microorganisms, C. cellulolyticum and C. phytofermentans had higher ethanol yields averaged across all substrates. Between these two bacteria, C. cellulolyticum had higher acetic acid production. Therefore, C. cellulolyticum has the greatest potential for ethanol and co-product production from lignocelluloses biomass. C. cellulovorans had the highest organic acid production on complex substrates. The effect of yeast extract concentration on growth and product formation by C. cellulolyticum and C. phytofermentans were also investigated. Tests within the range of 0.5-2.0 g/L yeast extract revealed that 2.0 g/L was the best concentration to ensure that nutrients were not the growth limiting factor.