Numerous diverse microorganisms reside in the cold desert soils of continental Antarctica, though we lack a holistic understanding of the metabolic processes that sustain them. Here, we profile the composition, capabilities, and activities of the microbial communities in 16 physicochemically diverse mountainous and glacial soils. We assembled 451 metagenome-assembled genomes from 18 microbial phyla and inferred through Bayesian divergence analysis that the dominant lineages present are likely native to Antarctica. In support of earlier findings, metagenomic analysis revealed that the most abundant and prevalent microorganisms are metabolically versatile aerobes that use atmospheric hydrogen to support aerobic respiration and sometimes carbon fixation. Surprisingly, however, hydrogen oxidation in this region was catalyzed primarily by a phylogenetically and structurally distinct enzyme, the group 1l [NiFe]-hydrogenase, encoded by nine bacterial phyla. Through gas chromatography, we provide evidence that both Antarctic soil communities and an axenic Bacteroidota isolate (Hymenobacter roseosalivarius) oxidize atmospheric hydrogen using this enzyme. Based on ex situ rates at environmentally representative temperatures, hydrogen oxidation is theoretically sufficient for soil communities to meet energy requirements and, through metabolic water production, sustain hydration. Diverse carbon monoxide oxidizers and abundant methanotrophs were also active in the soils. We also recovered genomes of microorganisms capable of oxidizing edaphic inorganic nitrogen, sulfur, and iron compounds and harvesting solar energy via microbial rhodopsins and conventional photosystems. Obligately symbiotic bacteria, including Patescibacteria, Chlamydiae, and predatory Bdellovibrionota, were also present. We conclude that microbial diversity in Antarctic soils reflects the coexistence of metabolically flexible mixotrophs with metabolically constrained specialists. Significance Diverse microbial life has been detected in the cold desert soils of Antarctica once thought to be barren. Here, we provide metagenomic, biogeochemical, and culture-based evidence that Antarctic soil microorganisms are phylogenetically and functionally distinct from those in other soils and adopt various metabolic and ecological strategies. The most abundant community members are metabolically versatile aerobes that use ubiquitous atmospheric trace gases to potentially meet energy, carbon, and, through metabolic water production, hydration needs. Lineages capable of harvesting solar energy, oxidizing edaphic inorganic substrates, or adopting symbiotic lifestyles were also identified. Altogether, these findings provide insights into microbial adaptation to extreme water and energy limitation and will inform ongoing efforts to conserve the unique biodiversity on this continent.

Tree stems are an important and unconstrained source of methane, yet it is uncertain whether internal microbial controls (i.e. methanotrophy) within tree bark may reduce methane emissions. Here we demonstrate that unique microbial communities dominated by methane-oxidising bacteria (MOB) dwell within bark of Melaleuca quinquenervia, a common, invasive and globally distributed lowland species. In laboratory incubations, methane-inoculated M. quinquenervia bark mediated methane consumption (up to 96.3 µmol m⁻² bark d⁻¹) and reveal distinct isotopic δ¹³C-CH₄ enrichment characteristic of MOB. Molecular analysis indicates unique microbial communities reside within the bark, with MOB primarily from the genus Methylomonas comprising up to 25 % of the total microbial community. Methanotroph abundance was linearly correlated to methane uptake rates (R² = 0.76, p = 0.006). Finally, field-based methane oxidation inhibition experiments demonstrate that bark-dwelling MOB reduce methane emissions by 36 ± 5 %. These multiple complementary lines of evidence indicate that bark-dwelling MOB represent a potentially significant methane sink, and an important frontier for further research.

Molecular hydrogen (H₂) is an abundant and readily accessible energy source in marine systems, but it remains unknown whether marine microbial communities consume this gas. Here we use a suite of approaches to show that marine bacteria consume H₂to support growth. Genes for H₂-uptake hydrogenases are prevalent in global ocean metagenomes, highly expressed in metatranscriptomes and found across eight bacterial phyla. Capacity for H₂oxidation increases with depth and decreases with oxygen concentration, suggesting that H₂is important in environments with low primary production. Biogeochemical measurements of tropical, temperate and subantarctic waters, and axenic cultures show that marine microbes consume H₂supplied at environmentally relevant concentrations, yielding enough cell-specific power to support growth in bacteria with low energy requirements. Conversely, our results indicate that oxidation of carbon monoxide (CO) primarily supports survival. Altogether, H₂is a notable energy source for marine bacteria and may influence oceanic ecology and biogeochemistry.

Significance: Termites are important decomposers of plant material in tropical ecosystems, and thereby produce globally significant amounts of the greenhouse gas CH ₄ . Here, we provide a mechanistic understanding of CH ₄ turnover in termite mounds to fill a long-standing knowledge gap. Using field measurements, we show that termite mounds oxidize, on average, half of the CH ₄ produced by termites before emission. This “hidden” biofilter mechanism is mediated by methanotrophic bacteria living in the mound walls or the soil beneath, for which internal termite-mound structures can facilitate CH ₄ transport. Process links within the mound stabilize the filter efficiency. Moreover, we estimate undisturbed termite biomass via CH ₄ emissions. This knowledge is crucial to reduce uncertainty in global termite-derived CH ₄ emissions.

The global methane (CH₄) cycle is largely driven by methanogenic archaea and methane-oxidizing bacteria (MOB), but little is known about their activity and diversity in pioneer ecosystems. We conducted a field survey in forefields of 13 receding Swiss glaciers on both siliceous and calcareous bedrock to investigate and quantify CH₄ turnover based on soil-gas CH₄ concentration profiles, and to characterize the MOB community by sequencing and terminal restriction fragment length polymorphism (T-RFLP) analysis of pmoA. Methane turnover was fundamentally different in the two bedrock categories. Of the 36 CH₄ concentration profiles from siliceous locations, 11 showed atmospheric CH₄ consumption at concentrations of ~1–2 μL L⁻¹ with soil-atmosphere CH₄ fluxes of –0.14 to –1.1 mg m⁻² d⁻¹. Another 11 profiles showed no apparent activity, while the remaining 14 exhibited slightly increased CH₄ concentrations of ~2–10 μL L⁻¹ , most likely due to microsite methanogenesis. In contrast, all profiles from calcareous sites suggested a substantial, yet unknown CH₄ source below our sampling zone, with soil-gas CH₄ concentrations reaching up to 1400 μL L⁻¹. Remarkably, most soils oxidized ~90 % of the deep-soil CH₄, resulting in soil-atmosphere fluxes of 0.12 to 31 mg m⁻² d⁻¹. MOB showed limited diversity in both siliceous and calcareous forefields: all identified pmoA sequences formed only 5 operational taxonomic units (OTUs) at the species level and, with one exception, could be assigned to either Methylocystis or the as-yet-uncultivated Upland Soil Cluster γ (USCγ). The latter dominated T-RFLP patterns of all siliceous and most calcareous samples, while Methylocystis dominated in 4 calcareous samples. Members of Upland Soil Cluster α (USCα) were not detected. Apparently, USCγ adapted best to the oligotrophic cold climate conditions at the investigated pioneer sites.