Lethla effect of nitrous acid on Escherichia coli

The bacterial tryptophan reverse mutation assay with Escherichia coli WP2

The Escherichia coli WP2 tryptophan reverse mutation assay detects trp(-) to trp(+) reversion at a site blocking a step in the biosynthesis of tryptophan prior to the formation of anthranilic acid. The different WP2 strains all carry the same AT base pair at the critical mutation site within the trpE gene. The assay is currently used by many laboratories in conjunction with the Ames Salmonella assay for screening chemicals for mutagenic activity. In general the WP2 strains are used as a substitute for, or as an addition to Salmonella strain TA102 which also carries an AT base pair at the mutation site. The assay is also recommended together with the Ames assay for data submission to regulatory agencies. National and international guidelines have been established for performing these mutagenicity assays. The E. coli WP2 assay procedures are the same as those described elsewhere in this volume for the Ames Salmonella assay (Mortelmans and Zeiger, 2000) with the exception that limited tryptophan instead of limited histidine is used. This chapter is an addendum to the previous chapter and the reader should refer to the previous chapter for details regarding experimental procedures and assay design.

Nitrite-induced mutations in a forward mutation assay: influence of nitrite concentration and pH

The mutagenicity of sodium nitrite at three pHs (7.4, 6.4 and 5.4) has been investigated by treating a shuttle vector plasmid in vitro and assaying for mutations within the supF target gene following replication of the damaged plasmid in human Ad293 cells. Mutation frequency increased with increasing nitrite concentration and decreasing pH. Among treatments from which a significant number of mutants could be collected, the most commonly induced mutations were GC-->AT transitions (44-56% of total mutations), followed by GC-->TA transversions (24-30%). The types of mutations induced at different nitrite concentrations and different pH's were similar, though some differences in their distribution throughout the supF gene were noted. These results provide information on the types of mutations that may be produced following the processing of nitrite-induced DNA damage in human cells.

An evaluation of tests using DNA repair-deficient bacteria for predicting genotoxicity and carcinogenicity. A report of the U.S. EPA's Gene-TOX Program

The detection of DNA-damaging agents by repair-deficient bacterial assays is based on the differential inhibition of growth of repair-proficient and repair-deficient bacterial pairs. The various methodologies used are described and recommendations are made for their improved use. In a survey of the literature through April 1979, 91 of 276 papers evaluated contained usable data, resulting in an analysis of 611 compounds that had been assayed in 1 or more of 55 pairs of repair-proficient and repair-deficient strains. The results indicate that (1) a liquid suspension assay is more sensitive than a spot (diffusion) test. In a review of the Escherichia coli polA assay, 45 compounds that gave "No Test" in the spot test were clearly positive or negative in the liquid suspension assay. (2) Of the 21 compounds analyzed by the E. coli polA assay and by other E. coli repair-deficient strains (e.g., rec, uvr, hcr, and exr derivatives of WP2 and AB1157), 10 were in complete agreement in all strains except uvrA strains. This indicates that strains other than polA+/polA- are useful for detecting DNA-damaging agents. However, in selecting strains for use in these assays, care should be taken to consider repair pathway specificity for particular compounds. (3) There was a 78% correspondence between results obtained with E. coli polA and Bacillus subtilis (H17/M45, 17A/45T) rec assay and between E. coli polA and Proteus mirabilis. (4) In a comparison of test results with carcinogenicity data, 44 of 71 (62%) carcinogenic compounds assayed by the polA system were positive, 10 (14%) were negative, and 17 (24%) gave No Test or doubtful results. 7 carcinogens were assayed by other E. coli strains and all were positive. 56 carcinogens were assayed in B. subtilis: 24 (43%) were positive, 9 (16%) were negative, and 23 (41%) gave No Test or doubtful results. Of the 7 carcinogens assayed in P. mirabilis, 6 (86%) were positive and 1 (14%) was negative. (5) The results were analyzed with respect to chemical classes. E. coli polA detected the highest percentage of hydroxylamines and alkyl epoxides. The B. subtilis rec assay detected the highest percentage of nitrosamines and sulfur and nitrogen oxides. It is concluded that some of these test systems are effective tools for the detection of DNA-damaging and potentially carcinogenic compounds, especially if the assay is done in liquid suspension and if more than 1 pair of tester strains is used. Advantages and disadvantages of the assay are discussed and suggestions are made for improvements in the system.

An evaluation of the Escherichia coli WP2 and WP2 uvrA reverse mutation assay

The methodology and status of the Escherichia coli WP2 reverse mutation system as it applies to chemical screening were reviewed using the available published literature. 163 documents were reviewed by the Working Group. These included abstracts, research articles, review articles and publicly available contract and grant final reports. From this group, 115 documents were rejected for critical evaluation by the Working Group. 48 documents were reviewed and the test results summarized. The general conclusion of the Working Group was the the E. coli WP2 reverse mutation system is a valuable tool for mutagenesis research, but that there is no evidence from a review of the literature that this assay will contribute significantly to the results obtainable from careful application of the Ames Salmonella assay. Another review of the role of this system in general screening may be warranted after more research and development with the plasmid-containing WP2 derivatives.