The Reversible Depression of Bacterial Luminescence during Exposure to X-Radiation

Abstract

Several years ago Hug and Wolf (1) demonstrated that the luminescence of Achromobacter fischerif growing on agar plates promptly declines on exposure to X-rays and promptly recovers when the exposure is stopped. They employed exposures in excess of 300,000 r delivered at dose rates of 25 to 100 kr/min. Under these conditions recovery was never complete; the fraction that did not recover bore a relation to the accumulated dose, whereas the initial rate of decline bore a direct relation to dose rate. The authors attributed the nonrecoverable part to damage to the enzyme involved and the recoverable part to an attack by radiation on some renewable unit of the light-producing system. Washed cells out of contact with nutrients, however, did not display any recovery. Since this is one of the few observations of immediate responses of biological systems to radiation, further investigation of this phenomenon appeared warranted. With suspensions of Photobacterium fischeri in buffered saline, we found it possible to produce the same phenomenon as above at much lower dose rates (less than 1 krad/min). Further, we found this phenomenon also to occur in vitro. In the cellfree steady-state enzyme system, however, postirradiation recovery is complete. The observations from this study suggest that reduced flavin mononucleotide3 is the radiation-sensitive component of the light-producing system, and that the nonrecoverable part of the luminescence seen with intact cells is due not to inactivation of luciferase but to damage to cellular processes supporting luminescence (2).