Metabolic activation of the genotoxic environmental contaminants 2- and 3-nitrofluoranthene in variants of Salmonella typhimurium TA98.

The mutagenic environmental pollutants 2-nitrofluoranthene (2-NFA) and 3-nitrofluoranthene (3-NFA), labelled with 3H and 14C respectively, were incubated with Salmonella typhimurium strain TA98, its nitroreductase-deficient variant TA98NR and its O-acetytransferase-deficient variant TA98/1,8-DNP6, to investigate the activity of these metabolic pathways under conditions approximating those of the Ames assay, hence their contribution to mutagenic potency. 2-Aminofluoranthene (2-AFA) was the major metabolite of 2-NFA (4 microM) in all three TA98 variants, isolated by reverse-phase HPLC and identified by UV-vis and NMR spectroscopy and mass spectrometry. 2-AFA was formed more slowly in TA98NR (65 pmol/h/ml resting phase bacterial broth, 1 to 2 x 10(9) bacteria/ml) than in TA98 (295 pmol/h/ml) or TA98/1,8-DNP6 (82 pmol/h/ml). 2-Acetamidofluoranthene (2-AAFA) was also identified in incubations with TA98 (80 pmol/h/ml), TA98NR (21 pmol/h/ml), and TA98/1,8-DNP6 (8 pmol/h/ml). 3-Aminofluoranthene (3-AFA, confirmed by UV-vis and NMR spectroscopy and mass spectrometry) was formed by all three variants from 3-NFA (4 microM): TA98, 1.76 nmol/h/ml; TA98NR, 0.55 nmol/h/ml; TA98/1,8-DNP6, 2.93 nmol/h/ml. 3-Acetamidofluoranthene (3-AAFA) was not detected in any of the variants. 3-AFA and 3-AAFA were less mutagenic than 3-NFA, and required S9 for activation. Mutagenicity of 3-NFA relative to initial nitroreduction rate was similar in TA98 and in TA98NR, but almost 10-fold lower in TA98/1,8-DNP6; hence O-acetylation considerably enhances the mutagenicity of reduction products of 3-NFA. Mutagenicity of 2-NFA relative to initial nitroreduction rate was similar in TA98 and in TA98/1,8-DNP6; the bacterial genotoxicity of 2-NFA is therefore largely independent of O-acetyltransferase activity. Ratios of mutagenicity to nitroreduction rate were similar in TA98 for 2-NFA and 3-NFA; differences in the potency of these isomers arise primarily from their respective suitabilities as substrates for nitroreductase enzymes.