Evidence for the existence of distinct nitroreductases in Salmonella typhimurium: roles in mutagenesis
Related Experiment Videos
Abstract:
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.
Insights
This study reveals distinct nitroreductase enzymes in Salmonella typhimurium responsible for chemical mutagenicity. Different gene products activate specific nitro-containing compounds, aiding in toxicity assessments.
Area of Science:
- Microbiology
- Toxicology
- Genetics
Background:
- Nitro-containing chemicals, including nitroheterocyclics and nitrated polycyclic aromatic hydrocarbons, are known mutagens.
- Previous research suggested multiple nitroreductase activities in Salmonella typhimurium are essential for the mutagenicity of these compounds.
Purpose of the Study:
- To investigate the specific gene products responsible for nitroreductase activities in Salmonella typhimurium.
- To differentiate the roles of various nitroreductases in the mutagenic activation of different classes of nitro-containing chemicals.
Main Methods:
- Utilized Salmonella typhimurium strains with specific nitroreductase deficiencies.
- Compared mutagenicity responses to niridazole, dinitropyrenes, and 4-nitroquinoline-1-oxide in wild-type and mutant strains.
- Constructed double mutants lacking multiple nitroreductase specificities.
Main Results:
- Strains lacking the nitroreductase for niridazole were not mutagenized by related compounds but remained sensitive to dinitropyrenes.
- Double mutants deficient in both identified nitroreductase specificities were successfully constructed.
- Nitroreductase-deficient strains retained sensitivity to 4-nitroquinoline-1-oxide, implying a third nitroreductase activity.
Conclusions:
- Nitroreductase activities in Salmonella typhimurium are mediated by distinct gene products with varying specificities.
- These findings clarify the enzymatic basis of nitro-compound mutagenicity and aid in toxicological risk assessment.