Syngas fermentation to fuels is a technology on the verge of commercialization. Low cost of fermentation medium is important for process feasibility. The use of corn steep liquor (CSL) instead of yeast extract (YE) in Alkalibaculum bacchi strain CP15 bottle fermentations reduced the medium cost by 27% and produced 78% more ethanol. When continuous fermentation was performed in a 7-L fermentor, 6 g/L ethanol was obtained in the YE and YE-free media. When CSL medium was used in continuous fermentation, the maximum produced concentrations of ethanol, n-propanol and n-butanol were 8 g/L, 6 g/L and 1 g/L, respectively. n-Propanol and n-butanol were not typical products of strain CP15. A 16S rRNA gene-based survey revealed a mixed culture in the fermentor dominated by A. bacchi strain CP15 (56%) and Clostridium propionicum (34%). The mixed culture presents an opportunity for higher alcohols production from syngas. (C) 2013 Elsevier Ltd. All rights reserved.