Some chemicals can cause DNA damage when entering living cells. In some cases, DNA damage can cause tumor formation. Therefore, it is important to investigate the effects of DNA damage (genotoxicity) in water that is used as a source for the preparation of drinking water. Het Waterlaboratorium investigates genotoxicity with the P53-CALUX bioassay, and with the Ames test. The Ames test is a bioassay based on different strains of the bacterium Salmonella Typhimurium. The Ames test has been used for about fifty years worldwide, to investigate chemicals on their ability to cause DNA mutations. Het Waterlaboratorium has different strains of the Ames test, each specific for a certain type of DNA damage, examples are strain TA98 (base pair substitution), strain TA100 (frameshift mutation) and strain YG7108 (alkylation). In all strains, metabolic activation of promutagens by a mix of liver enzymes can be included in the implementation.
Salmonella bacteria need the amino acid histidine to live. They can synthesize histadine themselves. For the development of the Ames test, genes that are required for the synthesis of histadine are deliberately mutated in such a way that bacteria loose this ability. When bacteria are exposed to mutagenic substances during an Ames test, reverse mutation occurs and the bacteria subsequently survive in an environment without histidine. This is measured by using a color response (purple / yellow).