SPECTRUM OF SPONTANEOUS AND 2,4,6-TRINITROTOLUENE (TNT)-INDUCED MUTATIONS IN SALMONELLA-TYPHIMURIUM STRAINS WITH DIFFERENT NITROREDUCTASE AND O-ACETYLTRANSFERASE ACTIVITIES

Spontaneous and 2,4,6-trinitrotoluene (TNT)-induced mutation spectra w ere determined at the hisD3052 allele of Salmonella typhimurium strain s TA98, YG1021 (nitroreductase-overproducing) and YG1024 (O-acetyltran sferase-overproducing). In TA98, 55% (11/20) of the spontaneous revers ions and 95% (19/20) of reversions in TNT-treated plates were deletion s of two bases at the same site (-2 hotspot deletions), whereas the re spective figures were 65% (13/20) and 80% (16/20) in YG1021, and 75% ( 15/20) and 95% (19/20) in YG1024. Other mutations observed in the TNT treatment were complex frameshifts consisting of either a -2 hotspot d eletion and a base substitution, or a +1 addition and base substitutio n at the stop codon. In addition, different kinds of deletions were re covered in the spontaneous spectra. The elevated enzymatic activities of strains YG1021 and YG1024, resulting in enhanced mutagenicity of TN T, did not seem to have an effect on the spectrum of TNT-induced mutat ions. However, the YG strains, which also have a higher spontaneous re vertant yield than the parental strain TA98, seemed to differ from TA9 8 in their spontaneous spectra. The increase consisted of revertants c ontaining the -2 hotspot deletion, possibly indicating elevated activa tion of exogenous or endogenous premutagens by the higher enzyme activ ities of the YG strains. (C) 1997 Elsevier Science B.V.