The Association for General and Applied Microbiology (VAAM), joining together about 3500 scientists interested in microbiology, honors with its Hans-Günter-Schlegel-Lecture outstanding scientific achievements for Microbiology in Germany. This honorary lecture is dedicated to Hans-Günter Schlegel, a former microbiology professor at Göttingen University, Germany, who has among many other achievements published the first encompassing microbiology textbook (“Allgemeine Mikrobiologie”) in German. In his honorary lecture on March 8, 2020 in the framework of the 6th joint conference of the VAAM and the DGHM in Leipzig (Germany), Michael was speaking about nitrifying microbes as the gatekeepers of the biogeochemical nitrogen cycle. His talk was delivered via video due to the current COVID-19 situation.