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The Intermediate metabolism of Pseudomonas Aeruginosa: a study of a new pathway of glucose oxidation Stokes, Flora Christina (Norris)

Abstract

The present study was undertaken in an effort to establish the oxidative pathway of glucose degredation by P. aeruginosa. It was postulated that because this organism had no anaerobic system of metabolism a study of the path by which it utilized glucose would reveal a system of carbohydrate breakdown not previously recognized in bacteria. A study of the endogenous respiration of the organism as an essential prerequisite to detailed studies of intermediate metabolism shows that the endogenous respiration of P. aeruginosa differs in several important respects from that reported for other organisms. The significance to be attached to the rate of endogenous respiration in interpreting data of the intermediate metabolism of micro-organisms is shown to be of great importance. The endogenous respiration of P. aeruginosa is found to function normally in the presence of substrate. Although the degree of oxidative assimilation is in agreement with figures reported in the literature, oxidative assimilation is not inhibited by usual concentrations of 2:4 dinitrophenol. Aeration of resting cells or storage at low temperatures do not reduce the endogenous respiration. Storage products of the organism as determined by R.Q. values are similar regardless of growth substrate. Since the oxidation of glucose by P. aeruginosa is governed by an adaptive enzyme system, it was thought that it would be a simple matter to eliminate or identify compounds as intermediates in glucose oxidation by the use of the technique of simultaneous adaption. Adaption studies with glucose-grown cells indicate that of the forty-three possible intermediates tested only gluconic acid could be an intermediate in glucose oxidation by this organism. Acetic acid has been isolated as an intermediate compound in the oxidation of glucose or ∝-ketoglutaric acid by P. aeruginosa. Cells of this organism produced under conditions of intense aeration were found to have lost the ability to oxidize acetic acid and this compound was found in large quantities in the growth medium. When these cells -were used in the oxidation of glucose, it was found that the oxygen consumed was the amount needed to convert glucose to acetic acid thus confirming the role of acetate as an intermediate in glucose oxidation. In contrast to the above-mentioned criterion the technique of simultaneous adaptation ruled out acetic acid as a possible intermediate in the oxidation of either glucose or ∝-ketoglutaric acid. The status of the theory of simultaneous adaption is discussed in relation to the data obtained. The technique of paper chromatography has been adapted to the identification of gluconic, 2-ketogluconic and ∝ -ketoglutaric acids as intermediates in glucose oxidation. Combinations of methyl and ethyl alcohol were found to be the most suitable solvents and ammoniacal silver nitrate was found to give the most satisfactory reaction. When grown under normal physiological conditions where glucose was metabolized to carbon dioxide and water P. aeruginosa was shown to have oxidized glucose by way of gluconic and 2-ketogluconic acids. Since a strong system for oxidizing both gluconic and 2-ketogluconlc acids was demonstrated, the presence of these acids over at least an eight hour period of growth is taken as evidence of their importance as intermediates in the oxidation of glucose by bacteria. This study establishes the presence of an aerobic system of glucose breakdown by P. aeruginosa which has not previously been recognized.

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