Simultaneous production of butanol and acetoin by metabolically engineered Clostridium acetobutylicum

Biobutanol is a potential fuel substitute and has been receiving increased attention in recent years. However, the economics of biobutanol production have been hampered by a number of bottlenecks such as high cost of raw material and low yield of solvent. Co-production of value-added products is a possible way to improve the economics of biobutanol production. Here, we present metabolic engineering strategies to substitute the major by-product acetone for a value-added product acetoin during butanol fermentation. By overexpressing the α-acetolactate decarboxylase gene alsD in Clostridium acetobutylicum B3, the acetoin yield was markedly increased while acetone formation was reduced. Subsequent disruption of adc gene effectively abolished acetone formation and further increased acetoin yield. After optimization of fermentation conditions, the alsD-overexpressing adc mutant generated butanol (13.8 g/L), acetoin (4.3 g/L), and ethanol (3.9 g/L), but no acetone. Thus, acetone was completely substituted for acetoin, and both mass yield and product value were improved. This study provides valuable insights into the regulation of acetoin synthesis and should be highly useful for the development of acetoin-derived products like 2,3-butanediol and 2-butanol in C. acetobutylicum.