Bioelectrochemical Reduction Of Carbon Dioxide To Acetate Using A Microbial Consortium Derived From The Cow Rumen

Pure cultures of chemoautotrophic microorganisms have previously been reported to produce acetate from carbon dioxide using reductive electric current. We hypothesized that electrofuel precursors could be produced in a similar manner from a consortium consisting of microbial populations acting as a stable community. This approach might offer improved efficiency and selectivity, greater sustainability, a more diverse group of end products, and more opportunities for community optimization in electrofuel production than is possible with pure cultures. To evaluate this concept, bovine rumen contents were enriched for autotrophic, anaerobic microbes for several generations using hydrogen and carbon dioxide for growth and energy. A stable acetogenic consortium was obtained and aliquots were transferred to the cathode compartments of bioelectrosynthesis cells with reductive electric current supplied to a biocathode by a potentiostat. Current uptake and biofuel precursor production were simultaneously measured over time for periods lasting from several days to several months. Acetate production rates near 3 millimoles per liter of biocathode volume per day were obtained. To evaluate that acetate production was derived solely from bioelectrochemical reduction of carbon dioxide a series of isotopic labeling experiments was performed. Growth medium was prepared using bicarbonate enriched with ten mole percent of 13C-labeled sodium bicarbonate. The 13C/12C isotopic ratios in acetate produced by the consortium growing only when current was provided were found by GC-MS analysis to be consistent with the expectation for acetate production from a carbon source (carbon dioxide or bicarbonate) that contained ten mole percent of a 13C label. This finding supports the hypothesis that acetate production in these bioelectrochemical cells is solely the result of microbial-catalyzed bioelectrochemical reduction of carbon dioxide / bicarbonate