Prophage X induction in Escherichia coli K12 envA uvrB: A highly sensitive test for potential carcinogens

A simple, inexpensive, and sensitive test for potential carcinogens based upon the property of carcinogens to. induce prophage X is described. By using chemicals activated with microsomal enzymes and E. coli K12 permeable (envA) tester bacteria also deficient in DNA repair (uvrB), the range of carcinogens detected in a lysogenic induction test (inductest) has been extended. We have provided the evidence that, after activation, carcinogenic polycyclic hydrocarbons such as ben-zo[alpyrene and 7,12-dimethylbenz[a]anthracene induce pro- phage X. Three variants of the test have been developed (in-ductests I, II, and III), which are as sensitive as the mutagenicity test of Ames et aL [Ames, B. N., McCann, J. & Yamasaki, E. (1975) Mutat. Res. 31, 347-364]. Inductests II and III provide a quantitative estimation of the inducing activity of a carcinogen. With the latter test, one can determine: (i) the cellular toxic effect of a carcinogen and (ii) the kinetics of appearance and disappearance of active metabolites. For two series of chemi- cals, aflatoxins and benz[alanthracenes, there is a good correlation between their carcinogenic activity in rodents and their prophage inducing activity in bacteria. The fact that the majority of