A Sensitive System (umu Test) for the Detection of Mutagenic Nitroarenes in Salmonella Typhimurium Strain Possessing Elevated Nitroreductase

Abstract

A sensitive test system for the detection of mutagenic nitroarenes in a new tester strain Salmonellatyphlmurium NM1011 with a high nitroreductase activity has been developed. The tester strain was constructed by subcloning the corresponding gene into pACYC184 plasmid, and introducingthe plasmid into TA1535 harboring a fusion gene umuc‘-'lacZ (pSK1002). The strain enablesus to monitor expression of the SOS function umuC, by measuring the β-galactosidase activity in the cells. The sensitivity of the NM1011 was compared with that of parent tester strain (TA1535/pSK1002), or a nitroreductase deficient strain in seventeen mutagenic/carcinogenic nitroarenes. The newly developed strains with a high nitroreductase activity had about 4 times higher nitrofurazone-reductase activity than the parent strain, and was found to be highly sensitive to the compounds such as 2-nitrofluorene (2-NF), 1-nitronaphthalene (1-NN), 2-nitronaphthalene (2-NN), 1-nitropyrene (1-NP), m-dinitrobenzene (m-DNB), 4,4’-dinitrobiphenyl (4,4’-DNB), 3-nitrofluoranthene, 3,7- and 3,9-dinitrofluoranthene, 5-nitroacenaphthene (5-NA), 1,6-dinitropyrene, and 2,4-dinitrotoluene (2,4-DNT). On the contrary, the enzyme-deficient strain did not show considerable responses to 2-NF, m-DNB, 1-NN, 2-NN, 1-NP, 4,4’-DNB, 2,4-DNT, and 5-NA. These results suggest that a newly developed tester strain that has high nitroreductase activity is very useful for the detection of mutagenic nitroarenes contaminating the water and urban atmosphere.