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UBC Theses and Dissertations

Survival of microorganisms under conditions of total starvation Potts, Joy Margaret

Abstract

Aerobacter aerogenes was shown to accumulate large quantities of a glycogen-1ike polysaccharide when grown under conditions of nitrogen deprivation and carbon excess. The majority of the reserve material was rapidly degraded during incubation in a non-nutrient medium; however, a decrease in carbohydrate to the structural level was obtained only after a four-day starvation period. Cells possessing the energy reserve compound contained a substantially reduced ribosomal complement relative to carbon-limited A. aerogenes and Pseudomonas aeruginosa which did not store this material. Ribosomes were degraded during starvation to barely detectable levels. In the non-nutrient environment, various intracellular components were degraded. Glycogen was the primary substrate for nitrogen-limited A. aerogenes, ribonucleic acid (RNA), for carbon-limited A. aerogenes and protein for nitrogen-limited P. aeruginosa. Correlating with the preferential utilization of RNA by carbon-limited A. aerogenes was the ability of this organism to oxidize ribose, one of the degradation products of RNA metabolism. P. aeruginosa was unable to degrade ribose but could efficiently oxidize most of the common amino acids and, therefore, protein was presumably the primary substrate during the endogenous metabolism of this organism. Survival curves of cells respiring endogenously revealed that glycogen-rich A. aerogeiies remained almost completely viable over a 24 hr. period of starvation whereas glycogen-deficient A. aerogenes or P. aeruginosa did not. However, once the rapid death rate of Aerobacter was initiated, the process continued until less than 1% of the original population remained viable. Conversely, although the death rate of P. aeruginosa was initially very fast, the number of viable cells at no time decreased to less than 6% of the original viable number. Alterations in the rates of transport of metabolites in A. aerogenes and P. aeruginosa did not correlate with maintenance of viability, as determined by the ability of cells to form colonies on plate count agar. It was concluded that the capacity to store a carbonaceous energy reserve is obviously a biological advantage to Aerobacter aerogenes. However, the ability of Pseudomonas aeruginosa to catabolize a wide range of substrates, coupled with the maintenance of its transport systems, must be more physiologically advantageous for the survival of a species than the ability to store carbonaceous reserves under certain limited growth conditions.

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