Superoxide dismutase and media dependence of far-UV radiation resistance in thiol-treated cells

Pretreatment of wild-type Escherichia coli K12 cells with dithiothreitol (DTT) induces far-UV radiation resistance after the thiol is removed (Claycamp 1988). The present study shows that a 1 h treatment of cells with DTT in minimal medium followed by a 0.5 h incubation in buffer (370C) results in a dose reduction factor (DRF) calculated at F37 of 1.81. When the thio pretreatment was in rich medium, sensitization occurs with DRF = 0.729. This could be reversed to protection by inhibiting extracellular thiol oxidation in rich medium with the chelator, DETAPAC, such that thiol oxidation rate was equivalent to that of DTT in minimal medium. Both thiol-induced resistance and sensitization produced changes predominantly in the shoulders of survival curves. For either protection or sensitization, at least one form of endogenous superoxide dismutase (SOD) was required. These results suggest that different targets are involved in thiol-induced UV protection and sensitization: DNA and extracellular targets (e.g. the membrane), respectively. (author)