Glucose Fermentation Pathway of Thermoanaerobium brockii

Abstract

T. brockii catabolized glucose via the Embden-Meyerhof-Parnas pathway into ethanol, acetic acid, H2-CO2 and lactic acid. Radioactive tracer studies, employing specifically labeled [14C]glucose, demonstrated significant fermentation of 14CO2 from C-3 and C-4 of the substrate exclusively. All extracts contained sufficient levels of activity (expressed in micromoles per minute per milligram of protein at 40.degree. C) to assign a catabolic role for the following enzymes: glucokinase, 0.40; fructose-1,6-diphosphate aldolase, 0.23; glyceraldehyde-3-phosphate dehydrogenase, 1.73; pyruvate kinase, 0.36; lactate dehydrogenase (fructose-1,6-diphosphate activated), 0.55; pyruvate dehydrogenase (CoA acetylating), 0.53; hydrogenase, 3.3; phosphotransacetylase, 0.55; acetaldehyde dehydrogenase (CoA acetyating), 0.15; ethanol dehydrogenase, 1.57; and acetate kinase, 1.50. All pyridine nucleotide-linked oxidoreductases examined were specific for NAD, except ethanol dehydrogenase which displayed both NAD and NADP-linked activities. Fermentation product balances and cell growth yields supported the glucose catabolic pathway described. Representative balanced end product yields (in moles per mole of glucose fermented) were: ethanol, 0.94; L-lactate, 0.84; acetate, 0.20; CO2, 1.31; and H2, 0.50. Growth yields of 16.4 g of cells/mol of glucose were demonstrated. Both growth and end product yields varied significantly in accordance with the specific medium composition and incubation time.