Fluctuation tests are more sensitive than plate tests in detection of chemicals which cause enhanced excision of transposon Tn10 in Salmonella typhimurium

Precise excision of transposon Tn10, as judged by reversion of Salmonella typhimurium strain LT2 trp1014::Tn10 to Trp+, was not detectably enhanced following exposure to 9-aminoacridine, 5-azacytidine or mitomycin C in conventional treat-and-plate assays. By contrast, 7/13 chemicals, including 5-azacytidine and mitomycin C, were found to be capable of enhancing precise excision of Tn10 when tested in modified fluctuation assays. Despite earlier reports, precise excision is one activity of transposons which is not therefore refractory to enhancement by chemical mutagens.