Metabolism of hexoses and pentoses by Cellulomonas uda under aerobic conditions and during fermentation

Abstract

Cellulomonas uda utilized the constituent carbohydrates of cellulose and hemicellulose under aerobic conditions and during fermentation. Balances of fermentation of cellobiose, glucose, xylose, L-arabinose, mannose, galactose, fructose, and sucrose were determined. Products formed were ethanol, L-lactic acid, acetic acid, formic acid, and succinic acid. In contrast to acetic acid, a small amount of succinic acid was utilized under aerobic conditions but only together with glucose. Ethanol was not consumed either under aerobic conditions or during fermentation. The rate of both glucose uptake and lactic acid excretion during fermentation increased with increasing initial pH values of 7 to 9. The intracellular concentration of ethanol at the end of glucose fermentation was 20 times higher than that in the culture supernatant. Switching from aerobic to fermentation conditions increased specific activities of fructose-6-phosphate kinase and fructose-1,6-bisphosphate aldolase, both key enzymes of the fructose-1,6-bisphosphate pathway, whereas those of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, key enzymes of the pentose phosphate cycle, were not affected significantly. Of the enzymes involved in pyruvic acid metabolism, pyruvate formate lyase, L-lactate dehydrogenase, and alcohol dehydrogenase were demonstrated in cell-free extracts. Fructose-1,6-bisphosphate had an activating effect on L-lactate dehydrogenase. Alcohol dehydrogenase was inhibited competitively by high concentrations of ethanol and noncompetitively by NAD.