Some Effects of Accelerated Charged Particles on Bacterial Spores

Abstract

SummaryDry spores of Bacillus megaterium were irradiated with stripped atoms accelerated in the heavy ion linear accelerator. Nine different ions were used, each at 8·3 MeV/nucleon, with specific energy losses (LET) varying from 5 keV/µ (total) for the ionized deuteron up to 500 keV/µ for the Ne10+ ion. Survival curves were constructed for each ion in three experimental conditions allowing distinction among three classes of damage; class I, the completely oxygen-independent damage; class II, that seen only when oxygen is present during irradiation; and class III, that produced by interactions between oxygen and free radicals.Class I increased with increasing LET up to 190 keV/µ while classes II and III are constant in this range. Beyond this, II and III decrease to zero approximately at 500 keV/µ, with I falling slightly. Cross-sectional values correspond with actual geometric dimensions of the spore: a high LET particle is lethal in any part of the protoplast; lower LET particles yield cross-sectional values that are smaller than morphologically distinct parts of the spore. A numerical analysis indicates two limiting cross-sections, one being possibly a single event process important at low LET, and the other a cooperative process that is the chief effect at high LET.