Survival and Macromolecular Synthesis During Incubation of Escherichia coli in Limiting Thymine1
Journal of Bacteriology
Survival and the synthesis of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein were measured during incubation of a thymine auxotroph of Escherichia coli in a series of media containing thymine concentrations below the optimal level of 2 ,g/ml. The rate of increase in viable count gradually diminishes to no net growth with 0.2 ug/ml. With lower concentrations of thymine, the rate of cell death gradually increases, resulting in a typical thymineless death curve with 0.02 ug/ml.
... th the rate of cell growth and the rate of cell inactivation vary linearly with the thymine concentration. Thirty minutes of incubation in media containing limiting concentrations of thymine before a shift to complete thymine starvation results in a progressive decrease in the length of the lag period preceding thymineless death. These data suggest that only one type of cellular damage occurs during the various degrees of thymine limitation. Prolonged preincubation in media containing 0.1 to 0.2 ug/ml of thymine results in an immunity to thymineless death. This immunity differs from that observed with amino acid-starved cells in its kinetics; ultraviolet irradiation of preincubated cells indicates that the cells are inactivated at the same rate as log-phase cells. These results suggest that the immunity is not associated with chromosome alignment. Thymine concentrations between 2 ' This paper is derived from a dissertation submitted by Charles E. Deutch to the Graduate Dvision, University of California, Riverside, in partial satisfaction of the requirements for the degree of Doctor of Philosophy. A portion of this work was presented at the 70th Annual Meeting of the