The Desert in Bottles: The Culturable Microbiome of the Atacama Desert's Grit Crust

Biological soil crusts (biocrusts) are associations of microorganisms coexisting in the top millimetres of soil, which are found predominantly in arid biomes. Recently, a new type of biocrust, termed grit crust, of the coastal range of the Atacama Desert was discovered. Here, we explore the culturable microbiome of the grit crust based on an integrative isolation approach combining morphological and phylogenetic analyses, focusing on cyanobacteria, green algae and the often overlooked non-lichenised fungi with climate records and soil data. The 122 generated isolates from four contrasting locations were distributed over three organismic groups: cyanobacteria (38), green algae (26) and non-lichenised fungi (58). The distribution of the organisms among the four locations followed a water availability gradient as shown by relative air humidity data, resulting in communities shaping the biochemistry of the substrate in terms of texture, carbon and nitrogen contents. Novel species, genera and the functional roles of the different organisms within the biocrust environment are discussed. The high abundance of endemic and presumably new species, including five potentially new genera within the cyanobacterial order of the Chroococcidiopsidales-not found in other deserts-underpins the uniqueness and further distinguishes the grit crust from other biocrusts in extreme environments.