Studies on the endogenous metabolism and senescence of starved Sarcina lutea

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Abstract
When washed suspensions of S. lutea are starved aerobically in phosphate buffer at the growth temperature of 37[degree], the rate of endogenous oxygen consumption decreases to very low values after 10 hr., although many of the cells survive for 40 hr. If starvation is prolonged further, the bacteria die at a rate of approximately 1.5% of the initial viable population per hour. Oxidation of intracellular free amino acids accounts for most of the observed endogenous oxygen uptake but RNA is also utilized and a portion of the component bases and pentoses is degraded and presumably oxidized. Ammonia appears in the supernatant and some pentose and ultraviolet-absorbing nucleotide are released from the cells. DNA, protein and polysaccharide are not measurably degraded. Survival can be correlated with the ability of aerobically starved bacteria to oxidize exogenous L-glutamate and glucose. When starved under nitrogen for 40 hr. cells continue to oxidize their endogenous reserves at undiminished rates when transferred to aerobic conditions; on prolonging anaerobic starvation the rate of oxidation declines during the period of most rapid loss of viability. In the presence of Mg2+, RNA degradation during aerobic starvation is almost completely suppressed without affecting the period for which the bacteria survive. Cells grown in peptone supplemented with glucose accumulate reserves of polysaccharide which are metabolized in aerobic starvation, together with free amino acids. Ammonia is evolved and RNA is degraded to a greater extent than in peptone-grown suspensions. Bacteria rich in polysaccharide survive less well than those which are deficient in the polymer; the reason for this phenomenon has yet to be established. In peptone medium, endogenous oxygen uptake and the concentration of intracellular free amino acids decline as growth progresses and they continue to decrease when the organism is held In stationary phase. Under the conditions used, the endogenous Qo2 ana free amino acid pool of cells grown in peptone with 2% (w/v) glucose did not decline so markedly and the bacteria contained large amounts of polysaccharide at all stages of growth.