Moorella thermoacetica is an anaerobic thermophilic acetogen that is capable of fermenting sugars, H-2/CO2 and syngas (H-2/CO). For this reason, this bacterium is potentially useful for biotechnology applications, particularly the production of biofuel from CO2. A soil isolate of M. thermoacetica, strain Y72, produces both ethanol and acetate from H-2/CO2; however, the maximum concentrations of these two products are too low to enable commercialization of the syngas fermentation process. In the present study, glycerol was identified as a novel electron sink among the fermentation products of strain Y72. Notably, a 1.5-fold increase in the production of ethanol (1.4 mM) was observed in cultures supplemented with glycerol during syngas fermentation. This discovery is expected to aid in the development of novel methods that allow for the regulation of metabolic pathways to direct and increase the production of desirable fermentative compounds. (C) 2015, The Society for Biotechnology, Japan. All rights reserved.