For over a century it was believed that methane (CH4) could only be oxidized by micro-organisms in the presence of oxygen. The possibility of nitrate-dependent or metal-dependent anaerobic oxidation of CH4 (AOM) was generally dismissed. However, about 6 years ago the microbes responsible for the nitrate-AOM reaction were discovered. This was followed by molecular approaches that resulted in the identification of the responsible Methylomirabilis oxyfera bacteria. Recently, the widespread environmental occurrence of these bacteria was demonstrated leading to the realization that AOM may play a significant role in the CH4 and nitrogen cycles. M. oxyfera is a unique microbe with unusual properties that we only begin to understand: the production of oxygen from NO by a putative NO dismutase and a very unusual polygonal cell shape. Even less is known about metals (Fe3+ or Mn4+) as electron acceptors for AOM. The aim of this project is to obtain a fundamental understanding of the metabolism and ecological importance of the M. oxyfera bacteria, and to enrich new metal-dependent AOM microbes. Such understanding contributes directly to our environment and economy because AOM is a new sustainable opportunity for nitrogen removal from wastewater. The results will show how the CH4, nitrogen and iron cycles are connected and may lead to new ways of mitigating methane emission. The biodiversity and contribution of AOM-microbes to the biogeochemical cycles in oxygen-limited ecosystems will be investigated, and new metal-AOM enrichments will be performed. Together the environmental and metabolic data will help to understand how and to what extent AOM-microbes contribute to the biogeochemical cycles and thus shape atmosphere of our planet. The research lines will employ state-of-the- art methods to unravel the exceptional properties of these highly unusual and important microbes. The experiments will be performed in one of the world best equipped laboratories for microbial ecology.