Engineering a Synthetic, Catabolically-Orthogonal Co-Culture System for Enhanced Conversion of Lignocellulose-Derived Sugars to Ethanol.

Fermentation of lignocellulosic sugar mixtures is often suboptimal due to inefficient xylose catabolism and sequential sugar utilization caused by carbon catabolite repression. Unlike in conventional applications employing a single engineered strain, the alternative development of synthetic microbial communities facilitates the execution of complex metabolic tasks by exploiting the unique community features, including modularity, division of labor and facile tunability. A series of synthetic, catabolically-orthogonal co-culture systems were systematically engineered, as derived from either wild-type Escherichia coli W or ethanologenic LY180. Net catabolic activities were effectively balanced by simple tuning of the inoculum ratio between 'specialist' strains, which enabled co-utilization (98% of 100 g L total sugars) of glucose-xylose mixtures (2:1 by mass) for both culture systems in simple batch fermentations. The engineered ethanologenic co-cultures achieved ethanol titer (46 g L), productivity (488 mg L h) and yield (~90% of theoretical maximum), which were all significantly increased compared to LY180 monocultures.