End-product synthesis and enzyme activities involved in pyruvate catabolism, H-2 synthesis, and ethanol production in mid-log (OD600 similar to 0.25), early stationary (OD600 similar to 0.5), and stationary phase (OD600 similar to 0.7) cell extracts were determined in Clostridium thermocellum ATCC 27405 grown in batch cultures on cellobiose. Carbon dioxide, hydrogen, ethanol, acetate and formate were major endproducts and their production paralleled growth and cellobiose consumption. Lactate dehydrogenase, pyruvate: formate lyase, pyruvate:ferredoxin oxidoreductase, methyl viologen-dependant hydrogenase. ferredoxin-dependant hydrogenase, NADH-dependant hydrogenase, NADPH-dependant hydrogenase, NADH-dependant acetaldehyde dehydrogenase, NADH-dependant alcohol dehydrogenase, and NADPH-dependant alcohol dehydrogenase activities were detected in all extracts, while pyruate dehydrogenase and formate dehydrogenase activities were not detected. All hydrogenase activities decreased (2-12-fold) as growth progressed from early exponential to stationary phase. Alcohol dehydrogenase activities fluctuated only marginally (<45%), while lactate dehydrogenase, pyruvate: formate lyase, and pyruvate:ferredoxin oxidoreductase remained constant in all cell extracts. We have proposed a pathway involved in pyruvate catabolism and end-product formation based on enzyme activity profiles in conjunction with bioinformatics analysis. (C) 2009 Elsevier B.V. All rights reserved.
