Key enzymes involved in end-product formation were identified in Thermoanaerobacterium saccharolyticum JW/SL-YS485, a thermophilic anaerobic bacterium under consideration as a biological catalyst for the conversion of cellulosic biomass to ethanol. Based on enzymatic assays and genome sequence analyses, pathways were identified that would lead to the generation of all major products from xylose fermentation: lactate, acetate, ethanol, hydrogen, and carbon dioxide. Pyruvate ferredoxin oxidoreductase is the primary pyruvate decarboxylating enzyme, producing carbon dioxide, reduced ferredoxin, and acetyl-CoA, and ferredoxin is likely oxidized by a specific hydrogenase. It is concluded that enzymes are present in this organism that could theoretically produce ethanol from carbohydrates at high yield. © 2008 Elsevier Inc. All rights reserved.