Biocrusts (BC) are intriguing communities composed of heterotrophic bacteria and fungi as well as photoautotrophic cyanobacteria, algae, mosses and lichens. Often referred to as the Skin of the Earth, latest estimates state that they cover about 12% of all terrestrial surface. BC are found globally where light is available but otherwise harsh conditions make the prevailing growth of higher plants impossible. They dominate arid regions such as the poles, deserts, and high alpine environments, where they are pivotal ecosystem engineers that offer a wide array of ecosystem services stabilising the soil surface, preventing erosion, fixing carbon and nitrogen, and building up organic soil biomass that enables later plant settlement. Moreover, BC immobilise heavy metals in contaminated soils, making them promising communities for bioremediation applications.

Despite their long-known ecological importance, many aspects of BC are still poorly understood. While their biogeography and ecology is well-researched, detailed studies are confined to few geographical regions, resulting in limited knowledge about both photo- and heterotrophic species composition. Biochemical and molecular processes underlying their ecological functions, interactions between the many different microorganisms that build a BC, and the role of secondary metabolites in these interactions are, with very few exceptions, still unknown. To investigate these intricate and important communities on a molecular level, model systems consisting of at least two organisms are needed. Such a system, however, so far only exists for cyanobacteria-dominated BC from temperate North American deserts, which is unsuited to study BC from other ecoregions like Europe, where BC are also found in cold climate zones like the Alps or the Arctic.

To develop a model system to investigate molecular mechanisms in BC from Europe, we isolated bacteria from an Arctic BC for further studies. Here, we present the first results of our work towards deciphering interactions within the living Skin of the Earth.