초록
<P><B>Abstract</B></P> <P> <I>Clostridium thermocellum</I> ferments cellulose, is a promising candidate for ethanol production from cellulosic biomass, and has been the focus of studies aimed at improving ethanol yield. <I>Thermoanaerobacterium saccharolyticum</I> ferments hemicellulose, but not cellulose, and has been engineered to produce ethanol at high yield and titer. Recent research has led to the identification of four genes in <I>T. saccharolyticum</I> involved in ethanol production: <I>adhE</I>, <I>nfnA, nfnB</I> and <I>adhA</I>. We introduced these genes into <I>C. thermocellum</I> and observed significant improvements to ethanol yield, titer, and productivity. The four genes alone, however, were insufficient to achieve in <I>C. thermocellum</I> the ethanol yields and titers observed in engineered <I>T. saccharolyticum</I> strains, even when combined with gene deletions targeting hydrogen production. This suggests that other parts of <I>T. saccharolyticum</I> metabolism may also be necessary to reproduce the high ethanol yield and titer phenotype in <I>C. thermocellum</I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Introducing four <I>T. saccharolyticum</I> genes significantly improved ethanol production. </LI> <LI> <I>adhA</I> expression was the most important for improving ethanol production. </LI> <LI> <I>nfnAB</I> and <I>adhE</I> <SUP>G544D</SUP> expression were of secondary importance. </LI> <LI> Eliminating hydrogen production reduced ethanol titer on high substrate loadings. </LI> <LI> Mg2<SUP>+</SUP> is an activator of the <I>T. saccharolyticum</I> AdhE enzyme. </LI> </UL> </P>