Cultivation-independent surveys have shown that the desert soils of Antarctica harbour surprisingly rich microbial communities 1-3 . Given that phototroph abundance varies across these Antarctic soils 2,4 , an enduring question is what supports life in those communities with low photosynthetic capacity 3,5 . Here we provide evidence that atmospheric trace gases are the primary energy sources of two Antarctic surface soil communities. We reconstructed 23 draft genomes from metagenomic reads, including genomes from the candidate bacterial phyla WPS-2 and AD3. The dominant community members encoded and expressed high-affinity hydrogenases, carbon monoxide dehydrogenases, and a RuBisCO lineage known to support chemosynthetic carbon fixation 6,7 . Soil microcosms aerobically scavenged atmospheric H 2 and CO at rates sufficient to sustain their theoretical maintenance energy and mediated substantial levels of chemosynthetic but not photosynthetic CO 2 fixation. We propose that atmospheric H 2 , CO 2 and CO provide dependable sources of energy and carbon to support these communities, which suggests that atmospheric energy sources can provide an alternative basis for ecosystem function to solar or geological energy sources 8,9 . Although more extensive sampling is required to verify whether this process is widespread in terrestrial Antarctica and other oligotrophic habitats, our results provide new understanding of the minimal nutritional requirements for life and open the possibility that atmospheric gases support life on other planets.Terrestrial Antarctica is among the most extreme environments on Earth. Its inhabitants experience the cumulative stresses of freezing temperatures, limited carbon, nitrogen and water availability, strong UV radiation, and frequent freeze-thaw cycles 2,10,11 . Although it was once believed that these conditions restrict life, we now know that the continent hosts a surprising diversity of macrofauna and microbiota 1,2,12 . Surveys indicate that the phylum-level composition of microbial communities in Antarctic soils is similar to those of temperate soils 3 , but Antarctic communities are highly specialized at the species level and strongly structured by physicochemical factors 1,3,10 . In many Antarctic soils, microorganisms are thought to live in dormant states 2 , with metabolic energy directed towards cell maintenance rather than growth 13 . However, it is unclear how these communities obtain the energy and carbon needed for maintenance, given that these soils are often low in organic carbon and contain few classical primary producers 2,5 .

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Despite decreasing costs, generating large-scale, well-replicated and multivariate microbial ecology investigations with sequencing remains an expensive and time-consuming option. As a result, many microbial ecology investigations continue to suffer from a lack of appropriate replication. We evaluated two fingerprinting approaches - terminal restriction fragment length polymorphism (T-RFLP) and automated ribosomal intergenic spacer analysis (ARISA) against 454 pyrosequencing, by applying them to 225 polar soil samples from East Antarctica and the high Arctic. By incorporating local and global spatial scales into the dataset, our aim was to determine whether various approaches differed in their ability and hence utility, to identify ecological patterns. Through the reduction in the 454 sequencing data to the most dominant OTUs, we revealed that a surprisingly small proportion of abundant OTUs (< 0.25%) was driving the biological patterns observed. Overall, ARISA and T-RFLP had a similar capacity as sequencing to separate samples according to distance at a local scale, and to correlate environmental variables with microbial community structure. Pyrosequencing had a greater resolution at the global scale but all methods were capable of significantly differentiating the polar sites. We conclude fingerprinting remains a legitimate approach to generating large datasets as well as a cost-effective rapid method to identify samples for elucidating taxonomic information or diversity estimates with sequencing methods.

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