Expanding Antarctic biogeography: microbial ecology of Antarctic island soils

The majority of islands surrounding the Antarctic continent are poorly characterized in terms of microbial macroecology due to their remote locations, geographical isolation and access difficulties. The 2016/2017 Antarctic Circumnavigation Expedition (ACE) provided unprecedented access to a number of these islands. In the present study we use metagenomic methods to investigate the microbial ecology of soil samples recovered from 11 circum-Antarctic islands as part of ACE, and to investigate the functional potential of their soil microbial communities. Comparisons of the prokaryote and lower eukaryote phylogenetic compositions of the soil communities indicated that the various islands harbored spatially distinct microbiomes with limited overlap. In particular, we identified a high prevalence of lichen-associated fungal taxa in the soils, suggesting that terrestrial lichens may be one of the key drivers of soil microbial ecology on these islands. Differential abundance and redundancy analyses suggested that these soil microbial communities are also strongly shaped by multiple abiotic factors, including soil pH and average annual temperatures. Most importantly, we demonstrate that the islands sampled in this study can be clustered into three distinct large-scale biogeographical regions in a conservation context, the sub-, Maritime and Continental Antarctic, which are distinct in both environmental conditions and microbial ecology, but are consistent with the widely-used regionalization applied to multicellular Antarctic terrestrial organisms. Functional profiling of the island soil metagenomes from these three broad biogeographical regions also suggested a degree of functional differentiation, reflecting their distinct microbial ecologies. Taken together, these results represent the most extensive characterization of the microbial ecology of Antarctic island soils to date.