초록
<▼1><P>Maximizing the conversion of biogenic carbon feedstocks into chemicals and fuels is essential for fermentation processes as feedstock costs and processing is commonly the greatest operating expense. Unfortunately, for most fermentations, over one-third of sugar carbon is lost to CO<SUB>2</SUB> due to the decarboxylation of pyruvate to acetyl-CoA and limitations in the reducing power of the bio-feedstock. Here we show that anaerobic, non-photosynthetic mixotrophy, defined as the concurrent utilization of organic (for example, sugars) and inorganic (for example, CO<SUB>2</SUB>) substrates in a single organism, can overcome these constraints to increase product yields and reduce overall CO<SUB>2</SUB> emissions. As a proof-of-concept, <I>Clostridium ljungdahlii</I> was engineered to produce acetone and achieved a mass yield 138% of the previous theoretical maximum using a high cell density continuous fermentation process. In addition, when enough reductant (that is, H<SUB>2</SUB>) is provided, the fermentation emits no CO<SUB>2</SUB>. Finally, we show that mixotrophy is a general trait among acetogens.</P></▼1><▼2><P>[GRAPHIC OMISSION]Microbial fermentation yield is limited by CO<SUB>2</SUB> loss in glycolysis. Here, the authors engineered <I>Clostridium ljungdahlii</I> for the anaerobic, non-photosynthetic mixotrophy production of acetone, increasing carbon product yield while reducing CO<SUB>2</SUB> emissions from a biogenic feedstock fermentation.</P></▼2>