The Survival of Starved Bacteria

SUMMARY: Samples of populations of Aerobacter aerogenes grown in continuous culture on a limited supply of glycerol died linearly with time without significant cryptic growth when aerated in buffered physiological saline at their growth pH and temperature. Death was uninfluenced by atmospheres varying from pure O2 to 2% O2 in N2 but was accelerated under N2 in media of various Eh values. Death was accelerated in environments of higher or lower tonicity, in unbuffered media, at pH values above 7, temperature above 40°, by strong illumination. Within limits, lower pH values or temperatures prolonged survival. Death was not immediately accompanied by breakdown of the osmotic barrier. Populations more dense than equiv. 20 μg. dry wt./ml. survived longer, sparser ones died more rapidly. The death rates of the populations studied were not influenced by 30% i-erythritol or by certain high molecular weight materials. Several metabolic inhibitors were tested; most of them accelerated death or had no effect; three protected transiently. Mg2+, Ca2+ or Fe3+ ions delayed death. A variety of trace elements, inorganic ions, growth factors, or an amino acid mixture, had no significant action; glycerol or intermediate compounds accelerated death. Dying populations showed rapid initial breakdown of intracellular RNA with release of phosphate and base fragments into the medium; most of the ribose was metabolized. Intracellular protein was degraded after a lag; intracellular polysaccharide and DNA were scarcely degraded at all. Endocellular reserves declined much more rapidly than did viability; the with glycerol and ‘glycerol dehydro-genase’ activity declined in parallel with viability. Populations permitted to grow at different rates died more rapidly the slower the growth rate; steady states were obtained by slow continuous culture in which constant proportions of the organisms were dead. For a given growth rate the nature of the limiting nutrient influenced the form of the survival curve: carbon, phosphorus, sulphur or oxygen limitations gave almost linear curves, N-limitation gave a sigmoid curve and Mg-limitation a concave form. In some instances the growth rate influenced the form of the survival curve and the death rate; Mg-limited organisms apparently died faster the faster they grew. The survival of stationary phase populations derived from batch cultures depended markedly on which chemical component of the environment limited growth; ‘logarithmic phase’ and ‘stationary phase’ C-limited organisms differed insignificantly in death rates. Partially synchronized populations from batch cultures died marginally more rapidly when harvested just after division ceased.