Co-production of butanol and iso-propanol using engineered Clostridium acetobutylicum

Abstract

A primary/secondary alcohol dehydrogenase (SADH, encoded by adh1) from Clostridium beijerinckii NRRL B-593 was introduced into C. acetobutylicum ATCC 824 under the control of adc promoter. The resulting strain was able to produce isopropanol with trace amount of acetone. An unwanted phenotype of the strain was lower titer of butanol than wild-type strain, possibly due to additional consumption of reducing equivalents during isopropanol production. In order to increase isopropanol and butanol production, a synthetic acetone operon (act operon) consisting of three homologous genes (adc, ctfA, and ctfB) was constructed using the adc promoter. Simultaneous expression of act operon and adh1 resulted in increased isopropanol production, and the butanol titer was comparable with wild-type. Finally, the fate of acetoin in engineered strains was investigated by gas chromatography and quantitative reverse transcription polymerase chain reaction.