Inactivation of Bacterial Spores by Charged Particles

概要

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Bacillus subtilis spores were bombarded with α-particles and heavy ions of carbon, nitrogen, and oxygen accelerated in the IPCR cyclotron. The maximum RBE was found at an unrestricted LET of about 120 keV・μpm^<-1> The effective inactivation cross section, Seff' for α-particles increased with LET, reaching a stationary level of S^<st>_α, 0.145μ^2. The analysis of the LET dependence revealed that several primary activations are required for producing one lethal-hit, within a very short length of the particle track. The value of S^<st>_α was lower than Seff for heavy ions (0.22〜0.26 μm^2). This discrepancy may be due to a difference of the repair capacities of "strand-target" between α-particles and heavy-ion bombardments, or to existence of a target (s) which is sensitive for bombarding particles of extremely high LET, or to a long-range effects caused by such high-LET particles. Dependence of sensitivities of bacterial cells to charged particles upon the linear energy transfer (LET) was demonstrated by many investigations. The basic mechanism for the bacterial inactivation by charged particles has been interpreted by the target theory assuming that DNA would be the cellular principal target.
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