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Quantification of ultraviolet-C irradiation induced cyclobutane pyrimidine dimers and their removal in Beauveria bassiana conidiospore DNA

     Department of Applied Microbiology and Food Science, College of Agriculture, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5A8 Canada

Ultraviolet (UV) radiation-induced DNA damage leading to entomopathogenic fungal inactivation is commonly measured by viability counts. Here we report the first quantification of UV-induced cyclobutane pyrimidine dimers (CPD) in DNA of the entomopathogenic fungus, Beauveria bassiana. Changes in the mobility of UV-C irradiated DNA were resolved with CPD specific bacteriophage T4 endonuclease V and alkaline agarose gel electrophoresis. The maximum number of CPD formed in B. bassiana DNA in vitro by UV-C irradiation was 28 CPD/ 10 kb after 720 J/m² dose. The maximum number of CPDs formed in B. bassiana conidiospore DNA irradiated in vivo was 15 CPD/10 kb after 480 J/m² dose and was quantified from conidiospores that were incubated to allow photoreactivation and nucleotide excision repair. The conidiospores incubated for photoreactivation and nucleotide excision repair showed decreased number of CPD/10 kb DNA and a higher percent survival of conidiospore populations than conidiospores not allowed to repair.

Key words: DNA damage, DNA repair, entomopathogenic fungi, T4 endonuclease V, ultraviolet irradiation