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 .

BackgroundMicrobial inhabitants of soils are important to ecosystem and planetary functions, yet there are large gaps in our knowledge of their diversity and ecology. The ‘Biomes of Australian Soil Environments’ (BASE) project has generated a database of microbial diversity with associated metadata across extensive environmental gradients at continental scale. As the characterisation of microbes rapidly expands, the BASE database provides an evolving platform for interrogating and integrating microbial diversity and function.FindingsBASE currently provides amplicon sequences and associated contextual data for over 900 sites encompassing all Australian states and territories, a wide variety of bioregions, vegetation and land-use types. Amplicons target bacteria, archaea and general and fungal-specific eukaryotes. The growing database will soon include metagenomics data. Data are provided in both raw sequence (FASTQ) and analysed OTU table formats and are accessed via the project’s data portal, which provides a user-friendly search tool to quickly identify samples of interest. Processed data can be visually interrogated and intersected with other Australian diversity and environmental data using tools developed by the ‘Atlas of Living Australia’.ConclusionsDeveloped within an open data framework, the BASE project is the first Australian soil microbial diversity database. The database will grow and link to other global efforts to explore microbial, plant, animal, and marine biodiversity. Its design and open access nature ensures that BASE will evolve as a valuable tool for documenting an often overlooked component of biodiversity and the many microbe-driven processes that are essential to sustain soil function and ecosystem services.

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Traditional microbiological methods of cultivation recover less than 1% of the total bacterial species, and the culturable portion of bacteria is not representative of the total phylogenetic diversity. Classical cultivation strategies are now known to supply excessive nutrients to a system and therefore select for fast-growing bacteria that are capable of colony or biofilm formation. New approaches to the cultivation of bacteria which rely on growth in dilute nutrient media or simulated environments are beginning to address this problem of selection. Here we describe a novel microcultivation method for soil bacteria that mimics natural conditions. Our soil slurry membrane system combines a polycarbonate membrane as a growth support and soil extract as the substrate. The result is abundant growth of uncharacterized bacteria as microcolonies. By combining microcultivation with fluorescent in situ hybridization, previously "unculturable" organisms belonging to cultivated and noncultivated divisions, including candidate division TM7, can be identified by fluorescence microscopy. Successful growth of soil bacteria as microcolonies confirmed that the missing culturable majority may have a growth strategy that is not observed when traditional cultivation indicators are used.