Construction and evaluation of a cea-lacZ gene fusion for the detection of environmental mutagens and carcinogens

The cea-kil operon of the ColE1 plasmid is negatively regulated by the LexA-repressor and therefore, it is under the control of SOS regulation. We constructed a gene fusion between the cea and lacZ genes. Expression of the translational fusion can be easily detected by monitoring the levels of beta-galactosidase. Since the whole detection system is plasmid-based, it can be used in both Escherichia coli and Salmonella typhimurium strains. The SOS-function-inducing activities of 14 chemical mutagens were investigated in E. coli K12 and in two S. typhimurium Ames-strains and compared with results obtained by the SOS-chromotest and by the Umu-test. To correct for the inhibitory effects of test chemicals on mRNA and/or protein synthesis, the level of the constitutive chloramphenicol acetyl transferase was assayed in parallel.