초록
<P><B>Abstract</B></P> <P>Gas fermentation using C1 substrate (CO or CO<SUB>2</SUB>) is a novel and attractive technology for ethanol production. <I>Clostridium autoethanogenum</I>, a promising gas fermentation strain, can grow on 100 % CO and produce acetate and ethanol through the Wood-Ljungdahl pathway. Like other autotrophic acetogens, <I>C. autoethanogenum</I> produces ethanol primarily via the reduction of acetyl-CoA. In this study, we demonstrated that ethanol was also formed via acetate reduction. <SUP>13</SUP>C-labeled acetate was employed to investigate the conversion of acetate in <I>C. autoethanogenum</I> during its autotrophic growth on CO. The addition of exogenous acetate can improve ethanol production in <I>C. autoethanogenum</I>, <SUP>13</SUP>C abundance in ethanol increased significantly with the increase of exogenous <SUP>13</SUP>C-labeled acetate, confirming that acetate can be transformed to ethanol. Moreover, transcriptional analysis of genes encoding phosphotransacetylase(pta), aldehyde:ferredoxin oxidoreductase(aor), carbon monoxide dehydrogenase(codh) and alcohol dehydrogenase(adh) in <I>C. autoethanogenum</I> revealed their differential expression under varied exogenous acetate levels. Among these genes, <I>pta</I> gene was down-regulated due to its involvement in acetate formation, whereas <I>aor</I> gene CAETHG_0102, <I>codh</I> gene CAETHG_3005, <I>adh</I> genes CAETHG_1841 and CAETHG_1813 were found to be highly up-regulated at higher levels of exogenous acetate, suggesting that they may play important roles in the conversion of acetate to ethanol.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ethanol production in <I>C. autoethanogenum</I> was improved in the presence of exogenous acetate. </LI> <LI> <SUP>13</SUP>C abundance in ethanol increased with the amount of <SUP>13</SUP>C-labeled acetate supplemented. </LI> <LI> Transcriptional level of <I>pta</I> gene was down-regulated in the presence of exogenous acetate. </LI> <LI> Genes CAETHG_0102, CAETHG_3005, CAETHG_1841 and CAETHG_1813 were highly up-regulated at higher levels of exogenous acetate. </LI> </UL> </P>