ABSTRACTMicrobial conversion of carbon dioxide to organic commodities via syngas metabolism or microbial electrosynthesis is an attractive option for production of renewable biocommodities. The recent development of an initial genetic toolbox for the acetogenClostridium ljungdahliihas suggested thatC. ljungdahliimay be an effective chassis for such conversions. This possibility was evaluated by engineering a strain to produce butyrate, a valuable commodity that is not a natural product ofC. ljungdahliimetabolism. Heterologous genes required for butyrate production from acetyl-coenzyme A (CoA) were identified and introduced initially on plasmids and in subsequent strain designs integrated into theC. ljungdahliichromosome. Iterative strain designs involved increasing translation of a key enzyme by modifying a ribosome binding site, inactivating the gene encoding the first step in the conversion of acetyl-CoA to acetate, disrupting the gene which encodes the primary bifunctional aldehyde/alcohol dehydrogenase for ethanol production, and interrupting the gene for a CoA transferase that potentially represented an alternative route for the production of acetate. These modifications yielded a strain in which ca. 50 or 70% of the carbon and electron flow was diverted to the production of butyrate with H2or CO as the electron donor, respectively. These results demonstrate the possibility of producing high-value commodities from carbon dioxide withC. ljungdahliias the catalyst.IMPORTANCEThe development of a microbial chassis for efficient conversion of carbon dioxide directly to desired organic products would greatly advance the environmentally sustainable production of biofuels and other commodities.Clostridium ljungdahliiis an effective catalyst for microbial electrosynthesis, a technology in which electricity generated with renewable technologies, such as solar or wind, powers the conversion of carbon dioxide and water to organic products. Other electron donors forC. ljungdahliiinclude carbon monoxide, which can be derived from industrial waste gases or the conversion of recalcitrant biomass to syngas, as well as hydrogen, another syngas component. The finding that carbon and electron flow inC. ljungdahliican be diverted from the production of acetate to butyrate synthesis is an important step toward the goal of renewable commodity production from carbon dioxide with this organism.
Converting Carbon Dioxide to Butyrate with an Engineered Strain of Clostridium ljungdahlii
