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.

Ecology and biogeochemistry of cyanobacteria in soils, permafrost, aquatic and cryptic polar habitats

“…Hypolithic communities have been reported from a number of Dry Valleys in the East Antarctic region and in other ice-free areas, with these sub-lithic communities typically dominated by cyanobacteria Khan et al 2011;de los Rios et al 2014). Antarctic hypolithic communities have been surveyed in considerable detail (Smith et al 2000;Wood et al 2008b;Pointing et al 2009;Makhalanyane et al 2013a).…”

“…The variability in the environmental factors, together with the less than ideal levels of nutrients required for biological activity, severely restrict microbial communities in polar environments. In the absence of other photoautotrophic clades, it is accepted that cyanobacteria are largely responsible for providing the most important ecosystem services, and that cyanobacterial autotrophy supports substantial and diverse populations of heterotrophic microorganisms (such as Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes) together with smaller numbers of organisms in higher trophic levels (Aislabie et al 2006;Babalola et al 2009;Chan et al 2012;Stomeo et al 2012;Makhalanyane et al 2013a;de los Rios et al 2014;Yung et al 2014).…”

“…Both classical and modern microbiological techniques have highlighted the presence of cyanobacteria in a wide range of terrestrial Arctic and Antarctic niches, including permafrost (Jansson and Tas¸ 2014), ice shelves Bottos et al 2008), rocks (Chan et al 2012;de los Rios et al 2014;Makhalanyane et al 2014), ponds and lakes (Taton et al 2003b;Bonilla et al 2005), glaciers and the resulting meltwater streams (Nadeau and Castenholz 2000;Jungblut et al 2005), and mineral soils (Wood et al 2008b; Lee et al 2012;Makhalanyane et al 2013a). Cyanobacteria are thought to be the primary colonizers in these niches (Vincent 2000), and are known to contribute to structural stability, moisture retention and fertility (Belnap and Gardner 1993).…”

“…Indeed, microbial components of cyanobacteria-driven biofilms produce large amount of exopolysaccharides (EPS), generating an exopolymer matrix where the biological and biogeochemical interactions take place (Paerl and Pinckney 1996;Nichols et al 2005). This EPS matrix also plays an important structural role in these microbial consortia (Dupraz et al 2009;de los Rios et al 2014) and is responsible for the creation and maintenance of microenvironments within relatively spacious pores (Ve´zina and Vincent 1997;Krembs et al 2002). EPS also facilitates important buffering, cryoprotection and desiccation protection for a wide range of microorganisms (de los Rios et al 2014).…”

“…This EPS matrix also plays an important structural role in these microbial consortia (Dupraz et al 2009;de los Rios et al 2014) and is responsible for the creation and maintenance of microenvironments within relatively spacious pores (Ve´zina and Vincent 1997;Krembs et al 2002). EPS also facilitates important buffering, cryoprotection and desiccation protection for a wide range of microorganisms (de los Rios et al 2014).…”