초록
<P><B>Background</B></P><P>Previously we have developed a butanol tolerant mutant of <I>Clostridium acetobutylicum</I> 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 <I>Clostridium beijerinckii</I> NRRL B593 was overexpressed in strain Rh8 under the control of <I>thl</I> promoter.</P><P><B>Results</B></P><P>The heterogenous gene <I>sADH</I> was functionally expressed in <I>C. acetobutylicum</I> 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.</P><P><B>Conclusions</B></P><P>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.</P>