A biochemical study of the diauxic growth of Pseudomonas aeruginosa

The growth of Pseudomonas seruginosa is an ammonium salts medium containing an organic acid and glucose as the sole sources of carbon and energy, results in the phenomenon of diauxic, i.e., double growth. Contrary to all previously recorded examples of this phenomenon in other organisms, the organic acid is utilized during the first growth cycle and glucose during the second. The oxidation of organic acids by cells grown on glucose as the sole source of carbon and energy, i.e., glucose-grown cells, and the oxidation of glucose by organic acid-grown cells, involves an initial period of induced protein synthesis. In the case of the oxidation of organic acids the permeases, protein components of the plasma membrane which facilitate the entry of the compounds into the cell, are inducible; the intracellular enzymes for organic acids are constitutive in this organism. A number of enzymes of glucose metabolism have been found in cells extracts. These are:- glucose and gluconic dehydrogenases; hexokinase, gluconokinase and 2-oxogluconokinase; glucose 6-phosphate and 6-phosphogluconate dehydrogenases; and 6-phosphogluconate dehydrase and 2-oxo-3-deoxy-6-phosphogluconate aldolase. These data are consistent with three pathways of glucose metabolism; the direct non-phosphorylative oxication to 2-oxogluconate; the Eatner-Doudroroff pathway; and the hexose monophosphate oxidative pathway. The enzymes of glucose metabolism studied are inducible in this organism. Methyl glucoside has been shown to be a non-metabolized inducer of the system for glucose metabolism, but no evidence was obtained for a single mechanism causing the accumulation of either [14C] methyl glucoside or [U-14C] glucose within the cells. Several results obtained, however, are indicative of the presence of an inducible permease for glucose, namely; (a) the difference observed between the oxidation of glucose by whole cells and disrupted cell preparations of cells grown on succinate and subsequently induced with glucose; (b) a comparison of the stability in glucose media of protoplasts prepared from citrate-grown cells before and after induction with glucose; (c) the continued synthesis of the enzymes of glucose metabolism when glucose-grown cells are inoculated into a growth medium containing glucose and citrate as carbon and energy sources. The metabolism of an organic acid does not affect the metabolism of glucose by non-proliferating cell suspensions which have been, (a) grown on glucose, (b) grown on glucose and subsequently induced by incubation with the organic acid, or (c) grown on glucose and subsequently induced by growth in the presence of both glucose and the organic acid. However, the metabolism of an organic acid does inhibit the metabolism of glucose by non-proliferating cell suspensions which have been grown on the organic acid and subsequently induced by incubation with glucose. This inhibition has been shown, in experiments with cell extracts, to be of the enzyme glucose dehydrogenase. The relevance of these results to the current hypotheses of the mechanisms of non-genetic control of metabolism is discussed