Rec-assay system

Kada, T., K. Hirano, and Y. Shirasu. Screening of environmental chemical mutagens by the Rec-assay system with Bacillus subtilis, pp. 149-173. In F.J. de Serres and A. Hollaender, Eds. Chemical Mutagens Principles and Methods for Their Detection. Vol. 6. 

Kada T, Hirano K, Shirasu Y. 1980. Screening of environmental chemical mutagens by the rec-assay system with bacillus subtilis. Chemical Mutagens 6 149-173. 

Kanematsu, N., Hara, M., and Kada, T., REC assay and mutagenicity studies on metal compounds screening of environmental chemical mutagens by the REC-assay system with Bacillus subtilis. Mutat. Res., 77, 109-116, 1980. 

Screening of Environmental Chemical Mutagens by the Rec-Assay System with Bacillus subtilis... 

Metals are probably one of the most susceptible forms in the B. subtilis rec-assay system. Among 121 metal compounds rec-assayed with cold incubation, 44 are positive (Table 8B). These were then examined as to their mutagenicity by the Ames assay, and some of them were found to be positive. The frequency of the mutagenic samples among the rec-assay-positive cases is rather limited compared to the other categories such as food additives and pesticides. It seems that further improvements are required in bacterial reversion assays for metal compounds. Most rec-assay-positive metals either are carcinogens or cause chromosome aberrations or gene mutations in cultured cells. 

Since the respiration of bacterial cells is directly and immediately converted to an electric signal, the preliminary screening of mutagens is possible within 1 h. Moreover, the microbial sensor system employs a homogeneous suspension. Consequently, the sensitivity of the microbial sensor is higher than the "rec-assay". The minimum measurable mutagen concentration is 1.6 jg ml-1 by the microbial sensor and 5.0 /jg ml"1 by the "rec-assay" and 10 p.g ml"1 by the Ames test (26) for AF 2. 

When DNA damage occurs, a number of repair systems can increase the cell s probability of survival. Several assays for genotoxicity rely on indirect measurement of the effects of these repair systems. TWo assays (the B. subtilis rec assay and the E. ooli DNA polymerase assay) measure reduction in the survival of chemically treated cells that lack at least one DNA-repair enzyme, compared with cells that have an intact repair system.198 373... 

In general, sodium selenite and sodium selenate have produced mixed results in bacterial mutagenicity test systems (Table 3M). Sodium selenite induced base-pair substitution mutations using S. typhimurium and was also positive in the transformation assay using Bacillus subtilis (Kramer and Ames 1988 Nakamuro et al. 1976 Noda et al. 1979). However, negative results have also been reported for sodium selenite both in S. typhimurium and the rec assay using B. subtilis (Lofroth and Ames 1978 Noda et al. 

Use of the rec-assay with B. subtilis in mutagenicity screeninghas been successful and enabled us to detect, in combination with other microbial systems, a number of environmental mutagens in a variety of substances such as... 

Since different types of DNA damage are subjected to cellular recombination repair, recombinationless bacteria are usually more sensitive than the wild type. Agents showing increased lethal activity on Rec in comparison with Rec" cells may have caused cellular DNA damage. Because of the simplicity of the procedures, positive chemicals are very easily selected and pooled even from a great number of samples. The DNA-damaging substances are then examined for specificity of induced mutations in bacterial systems. It has been shown that a majority of the rec-assay-positive chemicals are true mutagens. 

Use of the rec-assay procedures in conjunction with other bacterial systems such as the Ames reversion assays has been quite successful. The following examples include mainly results obtained by means of the rapid streak... 

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