Principles and Related Background of the Rec-Assay

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. 

Bacillus sub tilts (gram-positive) is useful in this assay because its cellular membrane is more permeable to chemicals than that of some gram-negative enteric bacteria. A recombination-deficient strain that has the highest sensitivity and the widest spectra to typical mutagens has been selected from a 

FIGURE 1. Radiation sensitivities of Bacillus subtilis strains, (a) gamma rays (b) UV. ( ) HI7 ReC (A) M45 Rec . From Sadaie and Kada.  

TABLE 1. Sensitivities of B. subtilis Strains Carrying Different Repair Deficiencies to Chemical Mutagens  

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