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.
