The Response of Radiation Resistant Bacteria Deinococcus Sp. to Oxidative Stress

Abstract

Bacteria of the radiation resistant genus 𝘋𝘦𝘪𝘯𝘰𝘤𝘰𝘤𝘤𝘶𝘴 have a high resistance to the lethal and mutagenic effects of many DNA damaging agents, however, the mechanisms involved in the response of these bacteria to oxidative stress are poorly understood. To investigate antioxidant enzyme responses in 𝘋𝘦𝘪𝘯𝘰𝘤𝘰𝘤𝘤𝘶𝘴 sp., the types of catalase and superoxide dismutase (SOD) produced by these bacteria were identified by visualization of the enzyme activities on non-denaturing polyacrylamide gels (PAGE) and the growth inhibition of selected strains by various concentrations of hydrogen peroxide and paraquat (a superoxide generating agent) was tested. 𝘋𝘦𝘪𝘯𝘰𝘤𝘰𝘤𝘤𝘶𝘴 sp. were found to be more resistant to hydrogen peroxide and more sensitive to paraquat than 𝘌𝘴𝘤𝘩𝘦𝘳𝘪𝘤𝘩𝘪𝘢 𝘤𝘰𝘭𝘪 K12. They possess relatively high levels of catalase and exhibit similar electrophoretic patterns on catalase zymograms compared to 𝘌. 𝘤𝘰𝘭𝘪, but all the tested strains produce only one SOD except 𝘋𝘦𝘪𝘯𝘰𝘤𝘰𝘤𝘤𝘶𝘴 𝘳𝘢𝘥𝘪𝘰𝘱𝘩𝘪𝘭𝘶𝘴 which produces two. The two catalases of 𝘋𝘦𝘪𝘯𝘰𝘤𝘰𝘤𝘤𝘶𝘴 𝘳𝘢𝘥𝘪𝘰𝘥𝘶𝘳𝘢𝘯𝘴 were found to be regulated independently. Cultures of 𝘋. 𝘳𝘢𝘥𝘪𝘰𝘥𝘶𝘳𝘢𝘯𝘴, when pretreated with sublethal levels of hydrogen peroxide, became relatively resistant to the lethal effects of H₂O₂ and exhibited higher levels of catalase than untreated control cultures. The pretreated cells were also relatively resistant to UV-and γ-ray-mediated lethality. These results suggest that 𝘋𝘦𝘪𝘯𝘰𝘤𝘰𝘤𝘤𝘶𝘴 sp. possess inducible defense mechanisms against the deleterious effects of oxidants and ionizing and UV radiation. The resistance to the lethal effects of hydrogen peroxide and UV radiation can not be induced by pretreatment with sublethal levels of hydrogen peroxide in 𝘋. 𝘳𝘢𝘥𝘪𝘰𝘥𝘶𝘳𝘢𝘯𝘴 rec30 mutant. Effects of manganese and magnesium on the growth and catalase activity of 𝘋. 𝘳𝘢𝘥𝘪𝘰𝘥𝘶𝘳𝘢𝘯𝘴 were determined. Homology between 𝘌. 𝘤𝘰𝘭𝘪 catalase and SOD genes and those of 𝘋𝘦𝘪𝘯𝘰𝘤𝘰𝘤𝘤𝘶𝘴 sp. was tested by Southern blot analysis using previously cloned genes from 𝘌. 𝘤𝘰𝘭𝘪.