(724d) Characterization of New Syngas-Fermenting Acetogens for Biofuel Production

Biofuel production via syngas fermentation is an emerging research area to address the demand for liquid fuels from lignocellulosic biomass, municipal solid and industrial wastes. Characterization of new strains and their fermentation capabilities are critical to move syngas fermentation technology towards commercialization. Syngas fermenting acetogens such as Clostridium ragsdalei, C. carboxidivorans, C. ljungdahlii, C. autoethanogenum and Alkalibaculum bacchi have been intensively studied. Novel and genetically modified syngas-fermenting strains are continuously being reported. In this study, the ability of three new clostridial strains (A, B and C) to ferment syngas to alcohol was compared with C. carboxidivorans strain P7A. All strains produced alcohols and carboxylic acids in serum-seal tubes. However, P7A was the best overall solvent producer (g/L ethanol, 0.8; butanol, 0.2 and hexanol, 0.1). Strain B, which is now laboratory-stable, was the best ethanol producer (1.2 g/L). Strain C, which uses carbohydrates poorly, showed potential for butanol (0.2 g/L) and hexanol (0.1 g/L) production. However, Strain C would require further development to enhance its activity. Larger-scale fermentations with these strains were performed in 250 mL bottle assays with 50 mL working volume at 37°C and 125 rpm. Syngas mixture CO:H₂:CO₂ (40:30:30) was fed for 264 h. Results showed that all strains converted CO and H₂ toalcohols and carboxylic acids. Ethanol and acetic acid production was nearly similar with all strains. As found in serum-seal tubes, P7A made more longer-chain alcohols and acids (g/L butanol, 1.2; hexanol, 0.4; butyric acid, 0.5; and hexanoic acid, 0.2) compared to other strains. The study demonstrates the potential of these new strains for syngas fermentation.