Fermentation end-product profiles of Clostridium cellulolyticum strains grown on various carbon sources. The C. cellulolyticum mutants were grown on defined VM media with D-glucose (5 g/l) in (A), D-cellobiose (5 g/l) in (B) crystalline Avicel cellulose (10 g/l) in (C), birch wood xylan (5 g/l) in (D), and acid-pretreated switchgrass (10 g/l) in (E). Lactate, acetate and ethanol concentrations were measured by high-performance liquid chromatography (HPLC), and the error bars represent standard deviations of measurements from three replicate cultures (except two replicate cultures were grown on xylan). Lactate concentrations were significantly lower in ldh and ldh mdh mutants compared to wild-type for growth on each substrate (P < 0.05, determined by analysis of variance (ANOVA) for (A-C) and by Student's t test for (D)). Acetate concentrations were also significantly lower in mdh and ldh mdh mutants compared to wild-type (P < 0.05). Ethanol concentrations were significantly higher in the ldh mdh mutant compared to wild-type (P < 0.05) for each substrate except glucose (A). (F) Shows results from quantitative saccharification of the residual biomass from wild-type and ldh mdh mutant cultures grown on acid-pretreated switchgrass and the acid-pretreated switchgrass substrate (before and after autoclaving).