Nitrofuran induced mutagenesis and error prone repair in Escherichia coli

Nitrofuran derivatives are a class of compounds which exhibit mutagenic and cytotoxic effects in bacteria and mammalian cells in tissue culture after metabolic activation by endogenous nitroreductases. The relationship between mutation and induction of pleiotropic error-prone repair functions (the 'SOS' system) in bacteria following exposure to nitrofurans was examined. A variety of nitrofurans were found to induce protein X, the recA+ protein, which is characteristic of error-prone repair. Furthermore, induction of the 'SOS' system depended on reductive activation of the mutagen. The use of a mutant thermally inducible for error-prone repair functions (tif-1) provided direct examination of bacteria exposed to non-lethal doses of nitrofuran. These results distinguish between mutants which arose from directly induced base mispairing and those which occur only after induction of error-prone repair functions. The mutational activity of AF2 (furylfuramide) was almost entirely dependent on the induction of error-prone repair since very few tryptophan revertants were detected in conditions which did not induced the 'SOS' repair system. We present a model for mutation induction by nitrofurans in bacteria.