Differential Modification of Oxic and Anoxic Components of Radiation Damage in Bacillus Megaterium Spores by Caffeine

Summary

Studies were carried out on the effect of caffeine on the X-irradiation sensitivity of B. megaterium spores with the following results: Caffeine exerts a concentration-dependent modifying action on oxygen-dependent components of X-ray-induced damage in B. megaterium spore suspensions causing an ‘over-O₂ effect’ at about 1 × 10⁻⁴ mol dm⁻³, and as the concentration is increased to 1 × 10⁻³ mol dm⁻³ or above, a small but consistent protection is seen. In the absence of O₂, at a wide range of concentrations (8·5 × 10⁻⁵ to 1 × 10⁻¹ mol dm⁻³), caffeine enhances the inactivation constant, k, from 1·17 to about 1·50 kGy⁻¹. Both ethanol and t-butanol (5 × 10⁻² mol dm⁻³) remove the ‘over O₂-effect’ produced by 1 × 10⁻⁴ mol dm⁻³ caffeine in O₂; such an effect, however, is not accompanied by reduction in the H₂O₂ concentrations in the spore suspensions. Ethanol prevents caffeine-induced anoxic sensitization, as well as H₂O₂ buildup. t-BuOH has no influence on either the low dose part of the log fraction survival curve or on the H₂O₂ yield in the spore suspensions. Caffeine reacts with radiation-induced e⁻_aq and ·OH with rate constants of 1·5 × 10¹⁰ and 6·9 × 10⁹ dm³ mol⁻¹s⁻¹, respectively.

• Caffeine
• Bacillus megaterium
• spores
• modification of radiation injury
• mechanisms of radiation damage