THE VITOTOX(R) TEST, AN SOS BIOLUMINESCENCE SALMONELLA-TYPHIMURIUM TEST TO MEASURE GENOTOXICITY KINETICS

A new test to detect genotoxicity, that we refer to as the VITOTOX(R) test, was developed. Four gene fusions that are based on the Escherich ia coli recN promoter were constructed and evaluated for their SOS res ponse-dependent induction. The wild-type recN promoter, a derivative m utated in the second LexA binding site, a derivative with a mutated -3 5 region, and a derivative from which both the second LexA binding: si te and the -35 region were mutated, were cloned upstream of the promot erless Vibrio fischeri luxCDABE operon of pMOL877, in such a way that lux became under transcriptional control of the recN promoter derivati ves. The inducibility by the SOS response of the promoter constructs w as tested in both E. coli and in the Ames test Salmonella typhimurium strains TA98, TA100 and TA104. In all strains, the highest sensitivity and induction was observed with the plasmids pMOL1067 and pMOL1068, t hat contain the lux operon under control of the recN promoter mutated in the second LexA binding site, or a recN promoter with a mutated -35 region, respectively. Therefore, strains containing pMOL1067 or pMOL1 068 were further used for genotoxicity testing. With the VITOTOX test, genotoxicity was detected within 1-4 h. The VITOTOX test is very sens itive: for most products tested, the minimal detectable concentration (MDC) values were considerably lower (5 to > 100 times) than those des cribed for the Ames test and the SOS chromotest. A good correlation wa s observed with the results from the Ames tests, but certain PAHs that are not mutagenic in the Ames test were genotoxic in the VITOTOX test . With the VITOTOX strains, the kinetics of SOS induction can be deter mined. This feature made it possible to distinguish between compounds in mixtures of genotoxic products so long as they had different induct ion kinetics.