The spatial structures of hypolithic communities in the Dry Valleys of East Antarctica

Abstract

Hypolithic communities represent important reservoirs of microbial life in hyper-arid deserts. A number of studies on the diversity and ecology of these communities from different geographic areas have been reported in the past decade, but the spatial distribution of the different components of these communities is still not understood. Moss- and cyanobacteria-dominated hypolithic communities morphotypes from Miers Valley (McMurdo Dry Valleys, East Antarctica) were analyzed by electron microscopy in order to characterize the micro-scale spatial structure. The two communities showed a high degree of internal organization, but differing according to the biological composition. In moss-dominated hypoliths, the moss plantlets are intermixed with mineral fragments of soil origin. However, in cyanobacteria-dominated hypoliths, a layered spatial organization was structured by filamentous cyanobacteria and associated extracellular polymeric components. While moss cells were lacking in cyanobacteria-dominated communities, biofilms formed by cyanobacteria and heterotrophic bacteria were observed in both community morphotypes. The waterholding capacity of both live and dead moss cells and the associated organic matrix, together with the protective properties of the extracellular polymeric substances, could facilitate the survival and activity of these communities. Similar structural strategies can favour the survival of microbial communities in different extreme environments.