초록
<P>We previously established a biomass pretreatment approach using acetic acid (which can be used as a carbon source for acetone-butanol-ethanol (ABE) fermentation) as the chemical catalyst, leading to comprehensive biomass utilization and enhanced solvent production (especially acetone production due to reassimilation of elevated fatty acids) using <I>Clostridium saccharoperbutylacetonicum</I>. However, acetone is corrosive to engine parts and cannot be used as a fuel. Thus, acetone produced during ABE fermentation is considered as an undesirable byproduct. In this study, we metabolically engineer <I>C. saccharoperbutylacetonicum</I> for isopropanol-butanol-ethanol (IBE) production by introducing secondary alcohol dehydrogenase gene to convert acetone into isopropanol. With either plasmid-based or CRISPR-Cas9-mediated chromosomal-integration-based overexpression, efficient IBE production was achieved. To further enhance solvent production, we additionally overexpressed <I>sol</I> operon (<I>ald</I>-<I>ctfA</I>-<I>ctfB</I>-<I>adc</I>), expression cassette EC (<I>thl</I>-<I>hbd</I>-<I>crt</I>-<I>bcd</I>) or <I>sol</I> in combination with EC. All resultant mutants generated elevated solvents, with one mutant produced 34.2 g/L IBE with a yield of 0.48 g/g. Finally, simultaneous saccharification and fermentation was carried out with the mutant using acetic-acid-pretreated switchgrass, and 16.2 g/L IBE was produced. Our engineered strain produced the highest IBE that has ever been reported in a batch fermentation. Our results indicated that acetic-acid-pretreated biomass can be efficiently converted into biofuel using metabolically engineered <I>Clostridium</I>.</P><P>Historically high-level isopropanol-butanol-ethanol (IBE; as a renewable biofuel) was produced from lignocellulosic feedstock with metabolically engineered <I>Clostridium</I> hosts.</P><BR>[FIG OMISSION]</BR>