Maider J. Echeveste Medrano and colleagues characterized the physiological and metabolic response of freshwater methanotrophic archaea to salt stress. The study performed metaproteomics, gene expression profiles and dedicated metabolomics to identify the pathways involved in the salt stress response and the osmolyte present in anaerobic methanotrophic archaea. Correspondence to Cornelia U. Welte c.welte@science.ru.nl