Engineering Clostridium beijerinckii for Butanol Production from Corn Cob

Corn cob is one of the most potential renewable feedstocks for bio-chemicals production. Hydrolysis of corn cob with dilute acid generates fermentable sugars (xylose, a little glucose and arabinose) and some microbial inhibitors. Most bacteria prefer glucose to xylose due to the carbon catabolite repression, therefore, the utilization efficiency of xylose and the tolerance to inhibitors of the producing strain must be improved for efficient biorefinery of corn cob. In this study, strain Clostridium beijerinckii was engineered to produce butanol from corn cob hydrolysate. To improve the tolerance to inhibitors, a successive mutation and adaptation process was developed. As well, heat-shock proteins GroESL from C. acetobutylicum, Thermoanaerobacter tencongenis, and Pseudomonas putida were investigated to enhance the hydrolysate tolerance of the cells. As a result, mutant SMB626 was derived, which produced 14.6 g/L solvent ABE (9.9 g/L butanol, 67.8%) from corn cob hydrolysate (containing 44.2 g/L xylose, 4.8 g/L glucose and some inhibitors) in 72 h fermentation. The yield of ABE from corn cob hydrolysast reached 0.37 g/g, which was comparable to that from corn mash.