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Rapid Immunoassays for Detection of UV-Induced Cyclobutane Pyrimidine Dimers in Whole Bacterial Cells

ABSTRACT Immunoassays were developed to measure DNA damage retained by UV-irradiated whole bacterial cells. Active Mycobacterium parafortuitum and Serratia marcescens cells were fixed and incubated with cyclobutane pyrimidine dimer-binding antibodies after being exposed to known UV doses (254 nm). When both fluorescent (Alexa Fluor 488) and radiolabeled (125I) secondary antibodies were used as reporters, indirect whole-cell assays were sensitive enough to measure intracellular UV photoproducts in M. parafortuitum and S. marcescens cells as well as photoenzymatic repair responses in S. marcescens cells. For the same UV dose, fluorescent DNA photoproduct detection limits in whole-cell assays (immunofluorescent microscopy) were similar to those in fluorescent assays performed on membrane-bound DNA extracts (immunoslot blot). With either fluorescent or radiolabeled reporters, the intracellular cyclobutane pyrimidine dimer content of UV-irradiated whole bacterial cells could be reliably quantified after undergoing a <0.5-order-of-magnitude decrease in culturability. Immunofluorescent microscopy results showed that photoenzymatic repair competence is not uniformly distributed among exponential-growth UV-irradiated pure cultures.