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Oxidative assimilation of glucose by Pseudomonas aeruginosa Duncan, Margaret Grace

Abstract

Manometric observations of the oxidation of glucose by washed cell suspensions of Pseudomonas aeruginosa grown on a glucose medium suggested that one-third to one-half of the substrate carbon was assimilated into cellular material. However, using uniformly-labelled glucose-C¹⁴ as the substrate it was found that during the period of rapid glucose oxidation only a small percentage of the C¹⁴ was assimilated into the cells, whereas a large quantity of ∝-ketoglutaric acid accumulated in the supernatant. A portion of the ∝-ketoglutaric acid was gradually oxidized after the disappearance of glucose, while the remainder was incorporated as ammonia became available from the breakdown of endogenous reserves. Most of the products of assimilation were nitrogenous and the addition of ammonia greatly increased the amount of C¹⁴ assimilated and prevented the accumulation of ∝-ketoglutaric acid; The cold TCA-soluble fraction and the lipid fraction appeared to be important during the early stages of assimilation, while the protein contained the largest amount of the incorporated radioactivity. The presence of azide increased the total oxygen consumption during glucose oxidation by the organism and this was accompanied by a significant decrease in the amount of radioactivity incorporated into the cells. The specific action of azide is most probably the uncoupling of oxidative phosphorylation for in the presence of high concentrations of azide there was little change in the relative amounts of the various products of assimilation, but the rate of formation was slower and the amounts synthesized were smaller. In contrast, chloramphenicol specifically inhibited the synthesis of protein while incorporation into the nucleic acid, lipid and cold TCA-soluble fractions was increased. Glucose-1-C¹⁴, glucose-2-C¹⁴ and glucose-6-C¹⁴ were also used as substrates. The results agreed with the observations of other workers that the Entner-Doudoroff and pentose phosphate pathways predominate in the oxidation of glucose by P. aeruginosa. Almost all the C-1 of glucose was eliminated as carbon dioxide and that which was incorporated was largely found in compounds such as amino acids, protein and nucleic acid which can be synthesized with the participation of carbon fixation. The C-2 of glucose was predominantly incorporated into lipid and the C-6 into nucleic acid which may be the result of the major role of the Entner-Doudoroff pathway in glucose catabolism. Carbon dioxide fixation appeared to be important in cellular synthesis and in the synthesis of ∝-ketoglutaric acid which undoubtedly arises via the tricarboxylic acid cycle. It appeared likely that the enzymes for ∝-ketoglutaric acid oxidation and transport of the compound into the cell were repressed by growth on a glucose medium. The oxidation of extracellular ∝-ketoglutaric acid by glucose-grown P. aeruginosa required protein synthesis and was prevented by the presence of chloramphenicol.

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