Determination of the genotoxic potential of water samples with the genetically engineered bacterium Salmonella typhimurium TA1535pSK1002.
In this way, genotoxins induce the umuC-gene, which belongs to the SOS-repairing system of the cell, which counteracts any damage to the bacterial genetic material. By combining the umuC-gene with the lacZ gene coding for the ß-galactosidase, the activation of the umuC gene can be indirectly determined by means of a colour formation. The induction rate (IR), defined as the ratio between the extinction at 420 nm and the one measured in the negative control, has been set as a measure for the genotoxicity. The test is performed both with and without S9-extract for the metabolic activation of genotoxins. The growth factor determined by the increase in the optical density at 600 nm is considered for the calculation of the induction rates. An inhibition of the bacterial growth is expressed by a reduced growth factor (WF) in relation to the control. Results with growth factors below 0.5 (50% growth inhibition) are not considered.
Test substances with an induction rate ≥ 1,5 are defined as genotoxic. For wastewater samples, the lowest value of the dilution step G (GEU-value), with an induction rate < 1.5, will be considered as the test result.
Test substance properties
The umu-test is applicable for water and waste water samples.