The ABE (acetone-butanol-ethanol) fermentation was one of the largest biotechnological processes ever known, and was once ranked second only to ethanol fermentation in scale of production. Among the three main products of ABE fermentation, butanol is the most expensive, followed by acetone and ethanol. The fluctuation of butanol price has a significant impact on the economics of ABE fermentation. Therefore, increasing the value and yield of target products, and utilization of cost-effective substrates, are expected to increase the cost competitiveness of ABE fermentation.

Clostridium beijerinckii naturally produces acetone, butanol, isopropanol and ethanol. Enlightened from this phenomenon, researchers of Dr. LI Yin’s lab at Institute of Microbiology, Chinese Academy of Sciences (IMCAS) designed an isopropanol biosynthesis module which consists of a secondary alcohol dehydrogenase gene from C. beijerinckii and a constitutive thl promoter from C. acetobutylicum. When this module was introduced into a butanol-tolerant and butanol hyper-producing C. acetobutylicum Rh8, which was obtained in a previous work (J. Proteome Res., 2010, 9:3046-3061), the acetone was completely converted to isopropanol through the the isopropanol biosynthetic pathway. Thus, the conventional ABE fermentation was switched to IBE (isopropanol-butanol-ethanol) fermentation, which has a higher value.

Isopropanol is one of the important buck chemicals with a wide variety of usage. The global demand for isopropanol is about 2.3 million tons per year. The development of IBE fermentation process provides an alternative route for the production of isopropanol. Furthermore, the mixed alcohols (isopropanol-butanol-ethanol) have the potential to be used as biofuel.

This work has been filed for a China patent and recently published on-line in the journal Biotechnology for Biofuels (http://www.biotechnologyforbiofuels.com/content/5/1/44). The first author, DAI Zongjie, is a postgraduate student of University of Science and Technology of China and IMCAS. This work was supported by National Basic Research Program of China (973 program, synthetic cell factories) and Knowledge Innovation Program of the Chinese Academy of Sciences.