Prof. Mike Jetten studies the ecology, physiology, biochemistry, metagenome and application of anaerobic micro-organisms, i.e. organisms that can survive without oxygen. These can be used, for example, to remove nitrogen and sulphur from water and air.

Jetten also studies the biogeochemical relevance of these micro-organisms.
He has made some significant discoveries about the role of anaerobic bacteria in the global nitrogen cycle (anammox) and nitrate-dependent methane oxidation.