Highly efficient continuous acetone–butanol–ethanol production from mixed sugars without carbon catabolite repression

Factors including the composition and concentration of mixed sugars, dilution rate, and cell density were examined to establish a highly efficient continuous acetone–butanol–ethanol (ABE)fermentation process using Clostridium saccharoperbutylacetonicum N1-4. During conventional continuous fermentation at a dilution rate of 0.15 h⁻¹, the glucose/xylose mixture exhibited carbon catabolite repression (CCR)with an intensity (I _CCR)of 4.18 and ABE productivity of 0.574 g L⁻¹ h⁻¹, while CCR was alleviated using a cellobiose/xylose mixture with 1.60 and 1.09 g L⁻¹ h⁻¹, respectively. Continuous fermentation with high cell density by cell recycling improved ABE productivity to 5.32 g L⁻¹ h⁻¹ at a dilution rate of 0.686 h⁻¹ owing to high xylose consumption. Further optimization of mixed sugar concentration in the feeding medium induced the best performance of continuous ABE production from mixed sugar without CCR, relative to previous studies: ABE productivity, 6.09 g L⁻¹ h⁻¹; ABE yield, 0.214 g g⁻¹; I _CCR, 1.48.