Microbial mutagenesis assays

Three primary tests are incorporated in the health effects area. The microbial mutagenesis assay is based on the property of selected Salmonella typhimurium mutants to revert from a histidine requiring state to prototrophy due to exposre to various classes of mutagens. The test can detect nanogram quantities of mutagens and has been adapted to mimic some mammalian metabolic processes by the addition of a mammalian liver microsomal fraction. The test is used as a primary screen to determine the mutagenic activity of complex mixtures or component fractions. 

COMPARISON OF REVERSE AND FORWARD MICROBIAL MUTAGENESIS ASSAYS Test System Mutations/10 surviving cells/yg... 

Sephadex LH-20 gel column with isopropanol followed by acetone. About 90% of the basic mutagenic activity is recovered in the acetone subfraction, which comprises approximately 0.5 wt% of the crude oil. Development of this separation scheme (Figure 5) was made possible by use of microbial mutagenesis assays as the detector during exploratory liquid chromatographic separations. Table 7 lists some of the preliminary data from these studies. 

Mutagenesis Assay Methodology 3.1. Microbial Mutagenesis Assays... 

Other microbial mutation, repair and recombination assays have also been used in chemical screening, however, the data base for carcinogenicity-mutagenicity correlation established with these in vitro test systems is relatively limited at this time.62-70 At present, the Ames Salmonella assay appears to be the most generally applicable screen for the detection of chemical mutagens. No other mutagenesis assay has been shown to respond to such a wide group of chemical types as the Salmonella mutants. 

The two purple adenine genes, ad-3A and ad-3B, are closely linked. By using a forced heterokaryon heterozygous for the ad-3 A and the ad-3B locus, Webber and de Serres were able to show that X-ray-induced specific-locus mutations in the ad-3 region were either point mutations or chromosome deletions (Webber and de Serres, 1965). The same classes of mutations are picked up in the specific-locus system in mice (Russell, 1951,1967). To sunmiarize in de Serres purple adenine system we have a eukaryotic, microbial assay system in which the same type of mutations can be isolated as in mammals. However, because it is a microbial system, it is considerably easier to perform quantitative mutagenesis studies with this system than with mice. 

H. S. Rosenkranz, W. T. Speck, and B. Gutter, Microbial assay procedures Experience with two systems, in In Vitro Activation in Mutagenesis Testing (F. J. de Serres, J. R. Foots, J. R. Bond, and R. M. Philpot, eds.), pp. 337-363, Elsevier/North-Holland, Amsterdam (1976). 

In studies with crude oils and effluents from synthetic fuel technology, we have used additional microbial assays to validate the results from Salmonella. Table 9 summarizes the comparative mutagenesis of selected test fractions in a variety of mutagenicity assays. 

Results with the selected test fractions have been given in detail and are shown qualitatively in Table 9. In general, the additional microbial assays reinforce the screening results with Salmonella. Discrepancies exist, however, in the mechanism of mutagenesis involved and the requirements(s) for metabolic activation. 

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