Increased sensitivity of the SOS-LUX-Test for the detection of hydrophobicgenotoxic substances with Salmonella typhimurium TA1535 as host strain

The SOS-LUX-Test is a simple and fast prokaryotic bioassay for the detectio n and quantification of genotoxic substances by the measurement of the DNA- damage proportional intensity of bioluminescence. This bioluminescence is p roduced by bacteria carrying the plasmid pPLS-1 with a lux operon under the control of a SOS promoter. In previous experiments different Escherichia c oli strains have been used as host bacteria. Depending on the degree of hyd rophobicity of the genotoxic substances the sensitivity of the SOS-LUX-Test was lower than measured in other bacterial bioassays for genotoxicity. An initial improvement could be made by using the E. coli strain PB3 with a to lC mutation causing an increased cell membrane permeability for hydrophobic substances compared to a tol wild-type strain. The change of the bacterial species from E. coli to a Salmonella typhimurium strain with a defect in t he synthesis of the outer cell membrane (rfa(-), strain TA1535) has led to a further increase in sensitivity. After a minor adaptation and modificatio n of the experimental procedure the results obtained with both strains were compared for the test substances NFO, ICR 191, MMC, NQO, NA, AA, 2-AF B(a) P. With hydrophobic substances the sensitivity of TA1535(pPLS-1) is higher than that of PB3(pPLS-1). This is correlated in most cases with a higher to xicity, whereas the sensitivity for water-soluble substances is not signifi cantly increased, as expected. From these results we decided to use the str ain S. typhimurium (also called S. choleraesuis ssp. choleraesuis) TA1535(p PLS-1) in the SOS-LUX-Test in future genotoxicity tests. (C) 2001 Elsevier Science B.V. All rights reserved.