Acetoin reductase (ACR) catalyzes the conversion of acetoin to 2,3-butanediol. Under certain conditions Clostridium acetobutylicum ATCC 824 (and derived strains) generates both D- and L-stereoisomers of acetoin, but due to the lack of an ACR enzyme, does not produce 2,3-butanediol. A gene encoding ACR from Clostridium beijerinckii NCIMB 8052 was functionally expressed in C. acetobutylicum under control of two strong promoters, the constitutive thl promoter and the late exponential adc promoter. Both ACR-overproducing strains were grown in batch cultures, during which 89-90% of the natively produced acetoin was converted to 20-22 mM D-2,3-butanediol. Addition of a racemic mixture of acetoin did lead to the production of both, D-2,3-butanediol and meso-2,3-butanediol. A metabolic network is proposed that is in agreement with the experimental data. Native 2,3-butanediol production is a first step towards a potential homo-fermentative 2-butanol producing strain of C. acetobutylicum.
- reductase/2,3-butanediol dehydrogenase
- transcriptional program
- butanol fermentation
- solvent production
- atcc 824