Quantitative forward mutation assay in Salmonella typhimurium using 8-azaguanine resistance as a genetic marker.

Abstract

We have developed a quantitative forward mutation assay using Salmonella typhimurium, in which resistance to the purine analog 8-azaguanine is used as a genetic marker. We present the assay protocol, the concentration-dependent toxicity and mutagenicity of five known mutagens (N-methyl-N'-nitro-N-nitrosoguanidine, ridine, dimethylnitrosamine, and benzo[alpyrene), and reconstruction experiments testing the assay for possible bias. The relative merits of forward versUs reverse mutation assays are discussed.Bacterial mutation assays are inexpensive, rapid, and easy to perform. Ames and his colleagues have developed a set of Salmonella typhimurium strains that are permeable to a wide range of chemicals and also are partially deficient in DNA repair (1). Both of these characteristics have been demonstrated to increase the sensitivity of the tester strains to chemical mutagens. The Ames tester strains commonly applied in screening for potential mutagens carry in toto three specific point mutations in the histidine operon, which must be reverted or suppressed in order to produce a histidine prototroph. This set of mutations includes one unknown base-pair substitution (hisG46) and two frameshift mutations (hisC3076 and hisD3052) for which the DNA sequence changes required have been determined (1). Use of data from independent assays with several strains

Source Contributions to the Mutagenicity of Urban Particulate Air Pollution

“…These source samples represent emission source types that accounted for ϳ80% of the fine particle emissions in the Los Angeles area in 1982. Of these 15 source samples, 10 were found to be mutagenic at the doses tested, and further biological analyses using both bacterial 28 and human cell 27 mutation assays were performed on the 10 mutagenic source samples. The mutagenic potency values shown in Table 1 represent the mutagenic strength (mutagenicity per mass of organics emitted) of a source sample in the mutation assay systems studied.…”

“…28,40 Briefly, the suspended bacteria underwent a 2-hr exposure to several dilutions of the sample. The exposure was done under two conditions, with or without the presence of 5% (v/v) Aroclor-induced postmitochondrial supernatant preparation (PMS, also referred to elsewhere as S9).…”

“…Mutagenicity Each of the 15 source samples shown in Table 1 was tested previously 36 in a bacterial mutagenicity assay (the S. typhimurium forward mutation assay of Skopek et al 28 ). These source samples represent emission source types that accounted for ϳ80% of the fine particle emissions in the Los Angeles area in 1982.…”

“…For purposes of comparison against earlier studies, the bacterial mutagenicity of the source and ambient samples also will be explored. The bacterial mutation assay used is a version of the S. typhimurium TM677 forward mutation assay developed by Skopek and coworkers, 28 which measures resistance to 8-azaguanine.…”

Seasonal and spatial variation of the bacterial mutagenicity of fine organic aerosol in southern california.

“…During transport, atmospheric chemical reactions can act to deplete the directly emitted organic compounds (15,16), while new compounds can be added to the aerosol, for example, via production of nitro-PAH and oxy-PAH as OH and NO3 radicals attack vapor-phase PAH (17)(18)(19)(20)(21)(22)(23)(24). Using bacterial mutagenicity assays (25,26), organic particulate matter filtered from ambient air has repeatedly been shown to be mutagenic (27)(28)(29)(30) (29) showed that the aerosol in industrial locations in Japan exhibits greater bacterial mutagenicity than samples taken at residential sites. Other investigators (31,34 have since shown that the bacterial mutagenicity of the ambient aerosol (per cubic meter of air sampled) differs between urban sites.…”