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Modification of Sensitivity to X-Irradiation by Water in Bacillus megaterium

1963; Radiation Research Society; Volume: 20; Issue: 2 Linguagem: Inglês

10.2307/3571533

1938-5404

A. Tallentire, E. L. Powers,

bioluminescence and chemiluminescence research

Dry spores of Bacillus megaterium were equilibrated at 25 deg C with partial pressures of H/sub 2/ ranging from 2.5 x 10/sup -5/ mm to 22 mm of mercury (= torr). After exposure to x rays rays, the spores with different water content were treated to permit recognition of the influence of varying amounts of H/sub 2/O in the spore on the previously described three main kinds of mechanisms responsible for lethal damage. Probability of damage from oxygen-independent causes is unchanged from about 10/sup -5/ torr to about 10/sup -1/ torr but may rise by about 20% as the vapor pressure is raised to saturation (22 mm at 25 deg C). Probability of damage from radiation-induced radicals that must combine with O/sub 2/ after formation decreases from the very dry (10/sup -5/ torr) spore to about one-third at 1 torr, remains constant to about 10 torr, and then decreases to zero at 22 torr. Water protects the spore from damage from these radicals, and to different degrees in two ranges of water content. Probability of damage observed only when O/sub 2/ present at the time of irradiation decreases from a high value at 10/sup -5/ torr to about one-fifth thatmore » value at 1 torr, remains constant to about 10 torr, and then increases as vapor pressure of H/sub 2/O increases to saturation. Results are analyzed and discussed. Water is seen to have a very large over-all protective effect; at the same time, it can be shown to be sensitizing in two ways, one O/sub 2/-independent and one O/sub 2/- dependent, as water content approaches maximal values. The evidence allows recognition of three levels of water content, as well as interpretation of the action of protective chemicals in wet cellular systems.« less