Introducing a single secondary alcohol dehydrogenase into butanol-tolerant Clostridium acetobutylicum Rh8 switches ABE fermentation to high level IBE fermentation
1 Department of Biochemistry and Molecular Biology, University of Science and Technology of China, Hefei, China
2 Institute of Microbiology, Chinese Academy of Sciences, No.1 West Beichen Road, Chaoyang District, Beijing, 100101, China
3 Graduate School of the Chinese Academy of Sciences, Beijing China
Biotechnology for Biofuels 2012, 5:44 doi:10.1186/1754-6834-5-44Published: 28 June 2012
Previously we have developed a butanol tolerant mutant of Clostridium acetobutylicum Rh8, from the wild type strain DSM 1731. Strain Rh8 can tolerate up to 19 g/L butanol, with solvent titer improved accordingly, thus exhibiting industrial application potential. To test if strain Rh8 can be used for production of high level mixed alcohols, a single secondary alcohol dehydrogenase from Clostridium beijerinckii NRRL B593 was overexpressed in strain Rh8 under the control of thl promoter.
The heterogenous gene sADH was functionally expressed in C. acetobutylicum Rh8. This simple, one-step engineering approach switched the traditional ABE (acetone-butanol-ethanol) fermentation to IBE (isopropanol-butanol-ethanol) fermentation. The total alcohol titer reached 23.88 g/l (7.6 g/l isopropanol, 15 g/l butanol, and 1.28 g/l ethanol) with a yield to glucose of 31.42%. The acid (butyrate and acetate) assimilation rate in isopropanol producing strain Rh8(psADH) was increased.
The improved butanol tolerance and the enhanced solvent biosynthesis machinery in strain Rh8 is beneficial for production of high concentration of mixed alcohols. Strain Rh8 can thus be considered as a good host for further engineering of solvent/alcohol production.