The structure and role of the cyanobacterial communities that colonise bare soils and fix nitrogen in the arctic ecosystem will be studied. The planned activities will focus on the isolation, identification and characterisation of cyanobacteria from arctic habitats and on the changes of the cyanobacterial community along a transect from a retreating glacier front to a more stable habitat characterised by the presence of mature vegetation. For these purposes, a polyphasic approach encompassing microbiological, morphological and molecular techniques will be applied to environmental samples and isolated cultures. The obtained results will give new insights on the diversity and role of nitrogen fixing cyanobacteria in the arctic and, in more general terms, on ecosystem development under changing climatic conditions.