Succinate production from xylose-glucose mixtures using a consortium of engineered Escherichia coli

The conversion of variable sugar mixtures into biochemicals poses a challenge for a single microorganism. For example, succinate has not been effectively generated from mixtures of glucose and xylose. In this work, a consortium of two Escherichia coli strains converted xylose and glucose to succinate in a dual phase aerobic/anaerobic process. First, the optimal pathway from xylose or glucose to succinate was determined by expressing either heterologous pyruvate carboxylase or heterologous adenosine triphosphate-forming phosphoenol pyruvate (PEP) carboxykinase. Expression of PEP carboxykinase (pck) resulted in higher yield (0.86g/g) and specific productivity (155mg/gh) for xylose conversion, while expression of pyruvate carboxylase (pyc) resulted in higher productivity (76mg/gh) for glucose conversion. Then, processes using consortia of the two optimal xylose-selective and glucose-selective strains were designed for two different feed ratios of glucose/xylose. In each case the consortia generated over 40g/L succinate efficiently with yields greater than 0.90g succinate/g total sugar. This study demonstrates two advantages of microbial consortia for the conversion of sugar mixtures: each sugar-to-product pathway can be optimized independently, and the volumetric consumption rate for each sugar can be controlled independently, for example, by altering the biomass concentration of each consortium member strain.