Metabolic engineering of end-product metabolism in T. saccharolyticum is described with the goal of increasing the yield of ethanol in lieu of organic acids. Using targeted gene knockout, a strain (ALK1) has been created that reliably produces ethanol at close to the theoretically maximum yield.  Elimination of acetate production is of particular note in that this involves significant changes in carbon and electron flux, ATP yield, and because stoichiometric production of ethanol was achieved in the absence of pyruvate decarboxylase, a key enzyme in yeast and previously engineered ethanol producing biocatalysts.  Notwithstanding the substantial metabolic changes accompanying elimination of organic acid production, strain ALK1 grows at a rate similar to the wild-type with slightly reduced cell yield.  Further development of this strain has yielded an organism (ALK2) which is capable of rapidly converting xylose and other sugars to ethanol at high yield and moderately high titer. 

T. saccharolyticum strain ALK2 is attractive for use in the conversion of cellulose to ethanol with commerical cellulase enzymes, since the elevated fermentation temperature allows the enzymes to function at their optimal temperature, lowering the cost for added cellulase.