Abstract
A comparative study was made of the kinetics of inactivation of Escherichia coli strain 15 T-A-U-by ultraviolet (u. v.) and by the decay of incorporated 32P atoms among different physiological states. The bacteria in logarithmic phase in the glucose medium were more sensitive to u. v. than those growing at lower rates in the succinate, aspartate and proline media. Having grown under the absence of protein synthesis, the bacteria became strikingly resistent to u. v. and had the same survivals irrespective of growth media. The u. v. sensitivity of 5-bromouracil (BU) substituted bacteria also varied reflecting the growth medium in which they incorporated BU into DNA. The sensitivity of the bacteria to the decay of 32P atoms that had been uniformly incorporated was not substantially altered by the change in growth conditions. A considerable fraction of 32P pulse-labeled cells in the succinate medium escaped from inactivation though the majority of those pulse-labeled in the glucose medium were susceptible. The relationship between the sensitivity of the bacteria to u. v. and 32P decay and the number of chromosomes per cell and DNA replication cycle, and also the character of the lethal damage induced by u. v. and 32P decay are discussed.
