Evidence for the existence of distinct nitroreductases in Salmonella typhimurium: roles in mutagenesis.

Previous studies on the mutagenicity of nitroheterocyclics and nitrated polycyclic aromatic hydrocarbons had indicted the probable existence in Salmonella typhimurium of a multiplicity of nitroreductase activities of varying specificities which are required for the expression of the mutagenicity of nitro-containing chemicals. In the present study evidence is presented that these activities reside in different gene products: (a) strains totally lacking in the nitroreductase which recognizes niridazole and related substances are not mutagenized by this group of chemicals and yet they are fully responsive to the mutagenic action of dinitropyrenes; (b) double mutants which have lost both types of specificities can be constructed. Finally, the presence of a third type of nitroreductase with a specificity for 4-nitroquinoline-1-oxide is implied by the finding that the nitroreductase-deficient strains described herein retain full sensitivity to the mutagenic action of this chemical.