S84: A comparison of the performance of carboxydotrophic Clostridium strains for use in syngas to ethanol fermentation

Syngas to ethanol fermentation is an emerging biofuel platform that circumvents 1^st generation ethanol’s food vs. fuel competition and 2^nd generation ethanol’s extensive pretreatment required for fermentation of sugars derived from lignocellulosic feedstocks. 

Several carboxydotrophic Clostridium strains with promising performance in terms of syngas to ethanol fermentation have been described.  To determine differences in ethanol production rates, ethanol to acetate ratios, and ability to thrive on minimal medium without addition of expensive nutrient supplements (yeast extract), Clostridium strains were grown in a 2-stage, continuous syngas fermentation system with minimal medium under conditions optimized for ethanol production.  The first stage of the system was kept in an acetogenic state by maintaining a constant pH of 5.5, while the pH in the second stage was lowered to induce solventogenesis, and the effect on ethanol to acetate ratios was monitored.  Among the strains, there were substantial differences in performance. Some strains were found not to grow well without yeast extract.  Research on addressing nutrient limitations, adaptation to it, and the relationship between biocatalyst density and ethanol production rates is currently underway.