Saccharification is one of the most critical steps in producing lignocellulose-based bio-ethanol through consolidated bioprocessing (CBP). However, extreme pH and ethanol concentration are commonly considered as potential inhibitors for the application of Clostridium sp. in CBP. The fermentations of several saccharides derived from lignocellulosics were investigated with a co-culture consisting of Clostridium themocellum and Clostridium thermolacticum. Alkali environments proved to be more favorable for ethanol production. Fermentation inhibition was observed at high ethanol concentrations and extreme pH. However, low levels of initial ethanol addition resulted in an unexpected stimulatory impact on the final ethanol productions for all cultures under selected conditions. The co-culture was able to actively ferment glucose, xylose, cellulose and micro-crystallized cellulose (MCC). The ethanol yield observed in the co-culture was higher (up to twofold) than in mono-cultures, especially in MCC fermentation. The highest ethanol yield (as a percentage of the theoretical maximum) observed was 75% (w/w) for MCC and 90% (w/w) for xylose. (C) 2011 Elsevier Ltd. All rights reserved.