A coculture-coproduction system designed for enhanced carbon conservation through inter-strain CO recycling.

Carbon loss in the form of CO is an intrinsic and persistent challenge faced during conventional and advanced biofuel production from biomass feedstocks. Current mechanisms for increasing carbon conservation typically require the provision of reduced co-substrates as additional reducing equivalents. This need can be circumvented, however, by exploiting the natural heterogeneity of lignocellulosic sugars mixtures and strategically using specific fractions to drive complementary CO emitting vs. CO fixing pathways. As a demonstration of concept, a coculture-coproduction system was developed by pairing two catabolically orthogonal Escherichia coli strains; one converting glucose to ethanol (G2E) and the other xylose to succinate (X2S). C-labeling studies reveled that G2E + X2S cocultures were capable of recycling 24% of all evolved CO and achieved a carbon conservation efficiency of 77%; significantly higher than the 64% achieved when all sugars are instead converted to just ethanol. In addition to CO exchange, the latent exchange of pyruvate between strains was discovered, along with significant carbon rearrangement within X2S.