INFLUENCE OF GROWTH MEDIUM ON ASSIMILATORY ACTIVITIES OF ESCHERICHIA COLI

EFFECTS OF GROWTH RATE AND LIMITING SUBSTRATE ON GLUCOSE METABOLISM IN ESCHERICHIA COLI

Wright, D. N. (Iowa State University, Ames), and W. R. Lockhart. Effects of growth rate and limiting substrate on glucose metabolism in Escherichia coli. J. Bacteriol. 89:1082-1085. 1965.-Escherichia coli was grown in continuous culture at various rates in a defined medium with either glucose of (NH(4))(2)SO(4) as the rate-limiting substrate. Cellular content of polysaccharide ("glycogen") is greater in cells grown under nitrogen limitation with glucose available in excess, and is greater in rapidly grown than in slowly grown cells. The ability of cells to carry on endogenous respiration, as measured by tetrazolium reduction, can be correlated with their glycogen content. In carbon-limited cultures, the proportion of substrate glucose diverted to glycogen production is least for cells grown slowly, which may reflect greater energy requirements for cell maintenance in such cultures. The activity of glucose-6-phosphate dehydrogenase (indicating function of a C-1 preferential pathway for glucose degradation) is greater in rapidly grown cells, confirming earlier observations in batch cultures. Activity of this enzyme is also greater in nitrogen-limited than in carbon-limited cells, suggesting that there may be catabolic repression of the Embden-Meyerhoff pathway when glucose is available in excess.

Aging of Escherichia coli

Clifton, C. E. (Stanford University, Stanford, Calif.). Aging of Escherichia coli. J. Bacteriol. 92:905-912. 1966.-The rates of endogenous and exogenous (glucose) respiration decreased much more rapidly than did the viable count during the first 24 hr of aging of washed, C(14)-labeled cells of Escherichia coli K-12 suspended in a basal salt medium devoid of ammonium salts. The rates of decrease of respiration and of death approached each other as the age of the cells increased, but death was not the only factor involved in decreased respiratory activity of the suspensions. The greatest decrease in cellular contents with aging was noted in the ribonucleic acid fraction, of which the ribose appeared to be oxidized, while uracil accumulated in the suspension medium. The viable count and respiratory activities remained higher in glucose-fed than in nonfed suspensions. Proline-labeled cells fed glucose tended to lose more of their proline and to convert more proline into C(14)O(2) than in unfed controls. On the other hand, uracil-labeled cells fed glucose retained more of the uracil than did nonfed cells, but glucose elicited some oxidation of uracil. An exogenous energy source such as glucose aided in the maintenance of a population, but it was not the only factor needed for such maintenance.

Influence of exogenous substrates on the endogenous respiration of Pseudomonas aeruginosa

Gronlund, Audrey F. (University of British Columbia, Vancouver, Canada), and J. J. R. Campbell. Influence of exogenous substrates on the endogenous respiration of Pseudomonas aeruginosa. J. Bacteriol. 91:1577-1581. 1966.-The influence of growth conditions, ammonium ions, and glucose concentration on endogenous respiration in Pseudomonas aeruginosa was determined by measuring C(14)O(2) evolution from uniformly labeled cells that had previously been grown on C(14)-glucose. A 93% suppression of endogenous C(14)O(2) evolution was evident under growth conditions, and a 66% suppression was observed in the presence of excess glucose. Increasing exogenous glucose concentrations supported decreasing levels of endogenous C(14)O(2) evolution. Ammonium ions slightly suppressed endogenous activity and enhanced the decrease in C(14)O(2) release observed with exogenous glucose. In addition, the effect of exogenous glucose, alpha-ketoglutarate, 2-ketogluconate, aspartic acid, and adenosine selectively on both endogenous ribonucleic acid (RNA) and protein oxidation was followed by measuring C(14)O(2) evolution from cells grown with C(14)-uracil or C(14)-proline. The five exogenous substrates examined suppressed endogenous RNA oxidation, and the degree of suppression appeared to be correlated with the amount of oxygen consumption and, hence, energy gained during the oxidation of these substrates. Oxidation of endogenous protein was decreased when cells were incubated with glucose, aspartate, and adenosine, but was increased when alpha-ketoglutarate and 2-ketogluconate were the exogenous substrates. The influence of the oxidizable exogenous compounds appeared to be related, in part, to the ammonium ion requirement imposed upon the cells for assimilation of the individual exogenous substrate.