MUTATION SPECTRA IN SALMONELLA OF COMPLEX-MIXTURES - COMPARISON OF URBAN AIR TO BENZO[A]PYRENE

We used an ion-exchange procedure coupled to the Salmonella assay to f ractionate the dichloromethane-extractable particulate organics from a n urban air sample collected in Boise, Idaho. A resulting base/neutral fraction contained 81% of the mutagenic activity but only 36% of the mass of the unfractionated sample. Chemical analysis showed that polyc yclic aromatic hydrocarbons (PAHs) accounted for much of the mutagenic activity of the air sample. Colony probe hybridization, PCR, and DNA sequence analysis were then used to determine the mutations induced by the complex mixtures and a model PAH, benzo[a]pyrene (BAP) in similar to 900 revertants of the frameshift hisD3052 allele and similar to 40 0 revertants of the base-substitution hisG46 allele. The majority (93- 94%) of the mutations induced at the frameshift allele in strain TA98 by the whole or base/neutral fraction of the urban air sample was a ho tspot 2-base deletion of a CG or GC within the sequence CGCGCGCG. The remaining mutations were complex frameshifts that consisted of -2 or 1 frameshifts associated with a flanking base substitution. BAP induce d a somewhat similar pattern of mvtations, with 70% being the hotspot mutation, 23% being complex frameshifts, and the remaining being delet ions. The inferred base-substitution specificity associated with the c omplex frameshifts at the hisD3052 allele (primarily G . C --> T . A t ransversions) was consistent with the observation that this same trans version was the primary mutation induced by the whole urban air sample and BAP at the base-substitution allele in strain TA100. At the frame shift allele, adducts that promote correct incorporation/ slippage cou ld account for hotspot mutations, whereas those that promote misincorp oration/ slippage could account for complex frameshifts. At the base-s ubstitution allele, a mixture of adducts or of adducts with multiple c onformations could account for the observed proportion of transitions and transversions. Combined with the bioassay-directed chemical analys is, these results from the first mutation spectra of a complex mixture suggest that such spectra reflect the dominance of particular classes of chemical mutagens within the mixture. (C) 1994 Wiley-Liss, Inc.