Heterologous expression of xylose specific transporter improves xylose utilization by recombinant Zymomonas mobilis strain in presence of glucose

Zymomonas mobilis is an exceptional ethanologen; however, rate of xylose utilization, by the engineered strains, lags far behind glucose. In the present study, an array of various potential candidate xylose specific transporters from Escherichia coli was constructed, under the influence of two different native Z. mobilis promoters. Effect of heterologous plasmid mediated expression of all the selected transporters in an evolved xylose utilizing Zymomonas strain, AD50, was screened towards improved co-utilization of glucose and xylose. Introduction of the xylose transporters, especially an ABC type transporter system, enhances the rate of xylose utilization by 48.9%, in presence of glucose by the novel engineered Z. mobilis strain, as compared to the control strain leading to notably reduced fermentation time and co-utilization of glucose and xylose coupled with improved ethanol production. The specific utilization rate of xylose in presence glucose was found to be 2.04 g g^-1 h^-1, which is comparable to that of glucose (2.49 g g^-1 h^-1). The ethanol titer was observed to be 47.4 g L^-1, with productivity and yield of 1.97 g L^-1 h^-1 and 0.472 g g^-1, respectively. The phenotypic response of the best performing strain was marked to be consistent under scale up conditions in a bioreactor.