Production of Isopropanol–Butanol–Ethanol Mixture by Engineered Clostridium acetobutylicum

The formation of by-products, mainly acetone, in the acetone–butanol–ethanol (ABE) fermentation significantly affects the yield. The team led by Chao Wang of Nanjing Tech University in China genetically-engineered Clostridium acetobutylicum to eliminate acetone production. The team also altered ABE fermentation to isopropanol–butanol–ethanol (IBE).

After introduction of secondary alcohol dehydrogenase into C. acetobutylicum XY16, the engineered XY16 completely eliminated acetone and converted it to isopropanol, indicating great potential for the production of IBE mixtures. Under the optimal pH level of 4.8, the total IBE production was significantly increased from 3.88 to 16.09 g/L, with final yields of 9.97, 4.98 and 1.14 g/L for butanol, isopropanol, and ethanol, respectively.

Furthermore, calcium carbonate could be both a buffer and activator for NAD kinase (NADK). Supplementation of calcium carbonate further improved IBE production to 17.77 g/L with 10.51, 6.02, and 1.24 g/L of butanol, isopropanol, and ethanol, respectively.