Microorganisms help to keep the water of lakes clean. In the process, they also detoxify the nitrogen compound ammonium, which is introduced into water bodies by fertilizers, for example, and is also produced naturally by metabolic processes. An international team led by the German Collection of Microorganisms and Cell Cultures (DSMZ) with IGB researchers Hans-Peter Grossart and Danny Ionescu has now shown that this detoxification of ammonium in the depths of European lakes is only sustained by an extremely small number of specific archaebacteria species.