Growth and mutation of bacteria during continuous irradiation.

For a long time now, microorganisms have been employed as a tool in the interpretation of the biological activities of radiations, usually in terms of lethal and genetic effect. In order to maintain standard conditions, recent investigations have been careful to prevent growth during irradiation. Whereupon, the lethal and genetic effects usually have been affected proportionately over a wide dosage range and indeed have been considered causally related (Lea, 1946). In studies of the genetic effects of absorbed radioactive isotopes, it is not possible to avoid the growth or metabolism of the organisms during irradiation. Radioactive material must be present in the ambient medium in order to have the isotope taken up. .Indeed, many workers have grown bacteria successfully in radioactive culture media, where equal or. smaller radiation levels have been shown to be rapidly lethal to the resting organisms (Schmidt, 1948; Hershey et al., 1951; Deysine aud Bonet-Maury, 1951; Harper and Morton, 1952). This study is concerned with the characteristics of bacterial growth during continuous irradiation and with a genetic change that occurs under such conditions. Since a widely prevalent concept attributes mutagenesis to errors in the synthesis of new genetic material (Muller, 1952), it has been of interest to examine mutagenic effect as a function of the amount of growth taking place during an irradiation period., Conversely, such a study also could indicate the contribution of genetic damage to the total lethal effects of radiation.