Microbial communities of Antarctic soil and lithic habitats

Abstract

Global climate change is predicted to significantly alter extreme terrestrial environments. The disturbance of desert ecosystems is predicted to profoundly alter key biological processes that are thought to be mediated by micro-organisms in these delicate biomes. The Antarctic Dry Valleys are a series of hyperarid polar deserts which are highly oligotrophic, experience near-constant below-freezing temperatures, and are critically low in bioavailable moisture. However, increases in surface temperatures and ultra-violet irradiation are predicted to supply endemic microbial communities with previously unattainable levels of moisture and nutrients as ice melt intensifies. Understanding the responses of local microbial populations to changes in moisture content is the critical focus of this study. Here microbial fingerprinting and pyrosequencing in combination with multivariate statistical analyses were utilised to address this knowledge deficit. This study presents evidence supporting the concept of ecological niche partitioning between local desert habitats (Pointing et al., 2009). Multivariate analysis of bacterial 16S rRNA gene-defined communities generated using T-RFLP showed that edaphic niches; hypoliths, endoliths, soils and mat communities, were distinct in structure. However, local Cyanobacterial populations were not delineated by habitat. Pyrosequencing data revealed that soil communities were highly diverse and are predicted to ‘seed’ development of specialised communities, such as hypoliths and endoliths, which supports the concept of species recruitment from soils in desert systems (Makhalanyane et al., 2013b). The role of moisture content was less significant in determining local bacterial diversity patterns according to the fingerprinting techniques applied here. However, pyrosequencing data suggested that Cyanobacterial abundance and diversity was greater in communities exposed to higher levels of moisture content. These data suggest that increases in local moisture content may influence Cyanobacterial population abundance and diversity in this desert environment. The increase in bioavailable moisture has the potential to lead to increased proliferation of the phylum as has been predicted previously (Wood et al., 2008). Taken together, these results appear to suggest that deterministic processes supersede stochastic events in determining diversity patterns across this polar desert. This may be critical in terms of global climate changes as rapidly changing environmental parameters may lead to detrimental changes in local desert community structures.