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Endogenous respiration of Pseudomonas aeruginosa during periods of prolonged starvation MacKelvie, Robin M.


During the investigation of the effect of age upon endogenous metabolism, advanced stationary phase cultures of Pseudomonas aeruginosa were found to be susceptible to cold-shock. The phenomenon was apparent through an increased oxygen uptake and an initial absence of extracellular ammonia during subsequent respiration at 30 C, which were shown to be due to the presence of an oxidizable substrate in the suspending fluid. Intracellular enzymes were released following the exposure of these cells to the cold, and a partial protection against damage was afforded by the addition of magnesium ions to the washing and suspending buffer. The storage of a reserve material for utilization during endogenous metabolism could not be demonstrated in cells grown for various periods of time in a chemically-defined medium which contained glucose in excess of that required for growth. Further, when not previously exposed to the cold, an immediate evolution of ammonia was observed when this organism was respired at 30 C irrespective of the medium in which it was cultured or the age at which it was harvested. The ribosome complement was seen to diminish during the prolonged incubation of cultures grown in the chemically-defined media, and was found to disappear almost completely when 48 hr cells, harvested from defined or complete media, were respired at 30 C for a further 48 hr. Chemical fractionation during the respiration period revealed an increase in the concentration of deoxyribonucleic acid and a decrease in the concentrations of ribonucleic acid and protein. Glucosamine was not found to be a major metabolite in the endogenous respiration of this organism. Progressive starvation resulted in a reduction in the constituitive enzymes and/or cofactors involved in the oxidation of glucose, and an ability to adapt to, and oxidize α-ketoglutarate was evident after a period of starvation which had reduced the ribosome complement to negligible proportions. Endogenously produced ammonia and acid-soluble UV-absorbing material were reincorporated upon the addition of an exogenous substrate following respiration for 48 hr, and a concurrent increase was recorded in the concentration of 50S ribosomes.

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