[Plasmid pSK1002-mediated mutator effect and SOS response in Salmonella typhimurium and its use for detection of mutagens].

The plasmid pSK1002 carrying the fused gene umuC'-'lacZ could increase the number of revertants induced by methyl methanesulfonate (MMS) and 4-nitroquinoline-1-oxide (4NQO) in S. typhimurium LT2 TA 1535(his-). Maximum revertants were 4.35 and 3.96 times that of the controls without the plasmid. The values induced by N-methyl-N'-nitrosoquanidine (MN-NG) were about the same with or without plasmid. However, the plasmid pKM101-mediated mutagenesis-enhancing effect was much greater than that through the mediation of pSK1002 as induced by the three mutagens mentioned above. Moreover, the plasmid pSK1002 could induce umu-mediated SOS response in the presence, of either mutagen stated above and mitomycin C(MMC). Maximum levels of beta-galactosidase (beta-gal) activity induced by four mutagens respectively were 4.56, 7.14, 4.94, and 3.42 times that of the controls, and a dose-response relationship was evident. The sensitivity of SOS response was superior to mutagenesis-enhancing effect. It showed that pSK1002 (umuC'-'lacZ) had a dual biological effect, namely, mutator effect and the effect of inducing SOS response. Besides, this study has proved SOS mutagenesis of 2,5-dichloronitrobenzol (2,5-DCNB). Because of the dual indicator nature of pSK1002, it is probable that pSK1002 would be further developed and applied in studying the relation between SOS response and mutagenesis, and monitoring environmental SOS mutagens.