Qualitative and quantitative assessment of genotoxins using SRRz lysis reporter under the control of a newly designed SOS responsive promoter in Escherichia coli

A new bacterial genotoxicity detection strain was constructed, in which the cell lysis gene of SRRz from a lambda phage was controlled by a new designed SOS responsive element, designated as Escherichia coli BL21/pUC-PST. The biosensor responded only after 0.5 h contact with mutagens and the changes in cell culture turbidity could be easily differentiated with the naked eyes from the control sample. This SOS/SRRz system presented a dose-dependent manner to five model DNA-damaging agents with an improved detection sensitivity. The limits of detection (LODs) were 0.026 μM for mitomycin C, 320.4 μM for azinphos-methyl, 34.4 μM for methyl methanesulfonate, 4.6 μM for dithianone and 6.0 μM for dichlofluanid, which were much lower than previously reported. By performing binary and ternary mixture experiments, the toxic equivalency concept was validated in the E. coli SOS/SRRz system by comparison with bioanalytical equivalent concentrations (BEQ) and overall toxic equivalent concentration (TEQ(mixture)) using Cr(vi) as the reference compound. Pearson analysis indicated that a strong correlation existed between the TEQ(mixture) and BEQ values. Thus the TEQ(mixture) could be presented as the Cr(vi) equivalent concentration from its dose–effect lysis profiles for the environmental sample. The proposed genotoxicity reporter strain allows for easier qualitative characterization and quantitative interpretation of the TEQ(mixture) values using Cr(vi) as the reference for environmental water samples.