초록
<P>Isopropanol represents a widely-used commercial alcohol which is currently produced from petroleum. In nature, isopropanol is excreted by some strains of <I>Clostridium beijerinckii</I>, simultaneously with butanol and ethanol during the isopropanol butanol ethanol (IBE) fermentation. In order to increase isopropanol production, the gene encoding the secondary-alcohol dehydrogenase enzyme from <I>C. beijerinckii</I> NRRL B593 (<I>adh</I>) which catalyzes the reduction of acetone to isopropanol, was cloned into the acetone, butanol and ethanol (ABE)-producing strain <I>C. acetobutylicum</I> ATCC 824. The transformants showed high capacity for conversion of acetone into isopropanol (> 95%). To increase isopropanol production levels in ATCC 824, polycistronic transcription units containing, in addition to the <I>adh</I> gene, homologous genes of the acetoacetate decarboxylase (<I>adc</I>), and/or the acetoacetyl-CoA:acetate/butyrate:CoA transferase subunits A and B (<I>ctfA and ctfB</I>) were constructed and introduced into the wild-type strain. Combined overexpression of the <I>ctfA</I> and <I>ctfB</I> genes resulted in enhanced solvent production. In non-pH-controlled batch cultures, the total solvents excreted by the transformant overexpressing the <I>adh</I>, <I>ctfA</I>, <I>ctfB</I> and <I>adc</I> genes were 24.4 g/L IBE (including 8.8 g/L isopropanol), while the control strain harbouring an empty plasmid produced only 20.2 g/L ABE (including 7.6 g/L acetone). The overexpression of the <I>adc</I> gene had limited effect on IBE production. Interestingly, all transformants with the <I>adh</I> gene converted acetoin (a minor fermentation product) into 2,3-butanediol, highlighting the wide metabolic versatility of solvent-producing <I>Clostridia</I>.</P>