Simultaneous fermentation of biomass-derived sugars to ethanol by a co culture of an engineered Escherichia coli and Saccharomyces cerevisiae

Microorganisms ferment xylose at high rate only when glucose concentration in the medium falls below a critical level. Since the specific productivity of product is highest during exponential to early stationary phase of growth, a glucose utilization negative ethanologenic E. coil (strain LW419a) was constructed for high rate of xylose fermentation in combination with Turbo yeast. This co-culture fermented all the released sugars in an acid/ enzyme-treated sugar cane bagasse slurry (10% solids) to an ethanol titer of 24.9 +/- 0.8 g.L-1 (70% of the theoretical yield) in < 30 h. Ethanol titer increased to 48.6 +/- 1.04 g.L-1 (yield, 0.45 g.g(-1) sugars) at a solids content of 20% and the highest rate of xylose consumption was 1.58 +/- 0.21 g.L-1.L-1. This study demonstrates the potential of a co-culture of strain LW419a and yeast to rapidly ferment all the sugars in pretreated biomass slurries to ethanol at their respective highest rates.