Hydrurus foetidus is a major primary producer in arctic and alpine streams all around the world. It is a single-celled algae, forming colonies of up to 30cm, consisting a mucosal tube with branches. It forms large blooms in winter, in snow-covered surroundings, under often very nutrient-restricted conditions. Preliminary work shows H. foetidus to have its own, specific microbiome, distinct from the surrounding stream water. This hints at a symbiotic relationship. The goal of our research is to shed light on the adaptive strategies of H. foetidus and investigate the role its microbiome is playing for its survival.