An Improved Strategy for the Utilization of Mixed Sugars from Lignocellulosic Hydrolysates

In the conversion of lignocellulosic biomass to ethanol, the five and six carbon sugars that are liberated from lignocellulosic hydrolysates cannot be readily converted to ethanol by any single microorganism. Even a strain with multiple metabolic pathways will leave significant portions of a given sugar unused due to preferential metabolism of the substrate sugars. As a result, yields are limited by differing fermentation rates and efficiencies, and the sugars present in hydrolysates are not completely converted to products. In addition, single strain approaches do not adapt readily to varying sugar ratios from different hydrolysate sources. This project will develop a dual strain approach for fermenting the five and six carbon sugars from lignocellulosic hydrolysates. Two strains will be constructed. The first strain will be able to consume five carbon sugars but not six carbon sugars; the second strain will be able to consume six carbon sugars but not five carbon sugars. To convert the mixed sugars from lignocellulosic hydrolysates into ethanol, a fermentation will be conducted using the two strains. Since the mixed strain population will be able to dynamically respond to the substrate supply, the fermentation will be able to adapt to the varying sugar ratios found in different hydrolystates and completely consume both sugars. Commercial Applications and other Benefits as described by the awardee: An increase in fermentation process flexibility should allow the use of a wider variety of biomass sources in ethanol production, increasing the usable supply of biomass. Reductions in unit price should result from increased process conversion rates. In combination, these factors should increase the ability of industrial bioconversion to meet chemical and fuel market demands.