Abstract
The arabinose resistance forward mutation assay was chosen for the development of bacterial strains in order to get specific mutagenic responses. Special strains of Salmonella typhimurium were constructed which show an elevated expression of nitroreductase and O-acetyltransferase. They were shown to be highly sensitive to mutagenic nitro-compounds (e.g. 1-nitropyrene and 1,8-dinitropyrene) and, after metabolic activation by rat liver S9-mix, also to mutagenic amino-compounds (2-aminoanthracene). Furthermore, strains of Escherichia coli with reduced expression of antioxidative enzymes (catalase and superoxide dismutase) were constructed. However, they were only moderately sensitive to oxidative mutagens such as quinones, nitrogen compounds, and the herbicide paraquat, because, in contrast to the Salmonella strains used, they build up a complete gram-negative cell wall. For this reason, the Escherichia strains were further genetically altered in order to make their cell wall penetrable to lipophilic compounds. This alteration increased the sensitivity to more lipophilic compounds. The strains were more sensitive to 1-nitropyrene by a factor of more than 10 and to 1,8-dinitropyrene by a factor of more than 100.
In order to validate the arabinose resistance test with the newly constructed strains, sediments of the whole German part of the Elbe River were examined. Overall mutagenicity (standard strains) as well as enhanced effects with the special strains were observed in sediment samples of the river. Mutagenic hot spots reflect direct industrial influences as well as hydrologic situations, which has led to concentration of the organic content of suspended matter, loaded with industrial or rural contamination. Generally, high mutagenic effects were observed where chemical analyses showed a high degree of contamination.
