(582br) Engineering Pentose Sugar Fermentation in Zymomonas Mobilis for Efficient Fuel Ethanol Production From Lignocellulosic Feedstocks

The bacterium Zymomonas mobilis is of interest for the commercial production of fuel ethanol from lignocellulosic feedstocks due to its high ethanol productivity. Z. mobilis has been engineered to ferment all of the sugars present in cellulosic biomass, but the digestion of five carbon sugars by the strain is still slow and inefficient. The inefficiencies are present because Z. mobilis displays preferential sugar digestion—only after all six carbon sugars in the culture medium are depleted will five carbon sugars be consumed.  We hypothesize that this is not due to an internal regulatory mechanism, but is instead due to the fact that Z. mobilis cannot efficiently transport pentose sugars into the cell. Therefore, in our work, we have investigated the effect on ethanol production of introducing dedicated pentose transporters in recombinant Z. mobilis. Our data reveal that the strains expressing the transporters can produce up to twice as much ethanol as the strains without them, indicating that this is an effective approach toward engineering cellulosic ethanol production by the strain. In addition, we have adapted pentose-fermenting Z. mobilis to growth on these sugars as sole carbon source. We have isolated strains with improved metabolic characteristics and are working to elucidate the genetic origins of these traits.