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Significant quantitative differences in end-product yields by two strains ofClostridium thermocellum and one strain ofThermoanaerobium brockii were observed during cellobiose fermentation. Most notably, the ethanol/H2 and lactate/acetate ratios were drastically higher forT. brockii as compared withC. thermocellum strains LQRI and AS39. Exogenous H2 addition (0.4 to 1.0 atm) during culture growth increased the ethanol/acetate ratio of bothT. brockii and AS39 but had no effect on LQRI. All strains had an operative Embden-Meyerhof glycolytic pathway and displayed catabolic activities of fructose-1,6-diphosphate–activated lactate dehydrogenase, coenzyme A acetylating pyruvate and acetaldehyde dehydrogenase, hydrogenase, ethanol dehydrogenase, and acetate kinase. Enzyme kinetic properties (apparentKm ,V max , and Q10 values) and the specificity of electron donors/acceptors for different oxidoreductases involved in pyruvate conversion to fermentation products were compared in the three strains. Both species contained ferredoxin-linked pyruvate dehydrogenase and pyridine nucleotide oxidoreductases. Ferredoxin-nicotinamide adenine dinucleotide (NAD) reductase activity was significantly higher inT. brockii than in AS39 and was not detectable in LQRI. H2 production and hydrogenase activity were inversely related to ferredoxin-NAD reductase activity in the three strains. Ferredoxin-NAD phosphate reductase activity was present in cell extracts of both species. Alcohol dehydrogenase activity inC. thermocellum was NAD dependent, unidirectional, and inhibited by low concentrations of NAD and ethanol. Ethanol dehydrogenase activity ofT. brockii was both NAD and NADP linked, reversible, and not inhibited by low levels of reaction products. The high lactate yield ofT. brockii correlated with increased fructose-1,6-diphosphate. The relation of catabolic enzyme activity and quantitative differences in intracellular electron flow and fermentation product yields of these thermophilic bacteria is discussed.

journal of bacteriology

Ethanol Production by Thermophilic Bacteria: Relationship Between Fermentation Product Yields of and Catabolic Enzyme Activities in <i>Clostridium thermocellum</i> and <i>Thermoanaerobium brockii</i>

Ethanol Production by Thermophilic Bacteria: Relationship Between Fermentation Product Yields of and Catabolic Enzyme Activities in Clostridium thermocellum and Thermoanaerobium brockii