| 1. |
- Emerson, Joanne B., et al.
(författare)
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Host-linked soil viral ecology along a permafrost thaw gradient
- 2018
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Ingår i: Nature Microbiology. - : Springer Science and Business Media LLC. - 2058-5276. ; 3:8, s. 870-880
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Tidskriftsartikel (refereegranskat)abstract
- Climate change threatens to release abundant carbon that is sequestered at high latitudes, but the constraints on microbial metabolisms that mediate the release of methane and carbon dioxide are poorly understood(1-7). The role of viruses, which are known to affect microbial dynamics, metabolism and biogeochemistry in the oceans(8-10), remains largely unexplored in soil. Here, we aimed to investigate how viruses influence microbial ecology and carbon metabolism in peatland soils along a permafrost thaw gradient in Sweden. We recovered 1,907 viral populations (genomes and large genome fragments) from 197 bulk soil and size-fractionated metagenomes, 58% of which were detected in metatranscriptomes and presumed to be active. In silico predictions linked 35% of the viruses to microbial host populations, highlighting likely viral predators of key carbon-cycling microorganisms, including methanogens and methanotrophs. Lineage-specific virus/host ratios varied, suggesting that viral infection dynamics may differentially impact microbial responses to a changing climate. Virus-encoded glycoside hydrolases, including an endomannanase with confirmed functional activity, indicated that viruses influence complex carbon degradation and that viral abundances were significant predictors of methane dynamics. These findings suggest that viruses may impact ecosystem function in climate-critical, terrestrial habitats and identify multiple potential viral contributions to soil carbon cycling.
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| 2. |
- Singleton, Caitlin M., et al.
(författare)
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Methanotrophy across a natural permafrost thaw environment
- 2018
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 12:10, s. 2544-2558
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Tidskriftsartikel (refereegranskat)abstract
- The fate of carbon sequestered in permafrost is a key concern for future global warming as this large carbon stock is rapidly becoming a net methane source due to widespread thaw. Methane release from permafrost is moderated by methanotrophs, which oxidise 20-60% of this methane before emission to the atmosphere. Despite the importance of methanotrophs to carbon cycling, these microorganisms are under-characterised and have not been studied across a natural permafrost thaw gradient. Here, we examine methanotroph communities from the active layer of a permafrost thaw gradient in Stordalen Mire (Abisko, Sweden) spanning three years, analysing 188 metagenomes and 24 metatranscriptomes paired with in situ biogeochemical data. Methanotroph community composition and activity varied significantly as thaw progressed from intact permafrost palsa, to partially thawed bog and fully thawed fen. Thirteen methanotroph population genomes were recovered, including two novel genomes belonging to the uncultivated upland soil cluster alpha (USCa) group and a novel potentially methanotrophic Hyphomicrobiaceae. Combined analysis of porewater delta C-13-CH 4 isotopes and methanotroph abundances showed methane oxidation was greatest below the oxic-anoxic interface in the bog. These results detail the direct effect of thaw on autochthonous methanotroph communities, and their consequent changes in population structure, activity and methane moderation potential.
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| 3. |
- Wilson, Rachel M., et al.
(författare)
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Hydrogenation of organic matter as a terminal electron sink sustains high CO2 : CH4 production ratios during anaerobic decomposition
- 2017
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Ingår i: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 112, s. 22-32
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Tidskriftsartikel (refereegranskat)abstract
- Once inorganic electron acceptors are depleted, organic matter in anoxic environments decomposes by hydrolysis, fermentation, and methanogenesis, requiring syntrophic interactions between microorganisms to achieve energetic favorability. In this classic anaerobic food chain, methanogenesis represents the terminal electron accepting (TEA) process, ultimately producing equimolar CO2 and CH4 for each molecule of organic matter degraded. However, CO2:CH4 production in Sphagnum-derived, mineral-poor, cellulosic peat often substantially exceeds this 1:1 ratio, even in the absence of measureable inorganic TEAs. Since the oxidation state of C in both cellulose-derived organic matter and acetate is 0, and CO2 has an oxidation state of +4, if CH4 (oxidation state -4) is not produced in equal ratio, then some other compound(s) must balance CO2 production by receiving 4 electrons. Here we present evidence for ubiquitous hydrogenation of diverse unsaturated compounds that appear to serve as organic TEAs in peat, thereby providing the necessary electron balance to sustain CO2:CH4 > 1. While organic electron acceptors have previously been proposed to drive microbial respiration of organic matter through the reversible reduction of quinone moieties, the hydrogenation mechanism that we propose, by contrast, reduces CAC double bonds in organic matter thereby serving as (1) a terminal electron sink, (2) a mechanism for degrading complex unsaturated organic molecules, (3) a potential mechanism to regenerate electron-accepting quinones, and, in some cases, (4) a means to alleviate the toxicity of unsaturated aromatic acids. This mechanism for CO2 generation without concomitant CH4 production has the potential to regulate the global warming potential of peatlands by elevating CO2:CH4 production ratios.
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| 4. |
- Woodcroft, Ben J., et al.
(författare)
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Genome-centric view of carbon processing in thawing permafrost
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 560:7716, s. 49-
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Tidskriftsartikel (refereegranskat)abstract
- As global temperatures rise, large amounts of carbon sequestered in permafrost are becoming available for microbial degradation. Accurate prediction of carbon gas emissions from thawing permafrost is limited by our understanding of these microbial communities. Here we use metagenomic sequencing of 214 samples from a permafrost thaw gradient to recover 1,529 metagenome-assembled genomes, including many from phyla with poor genomic representation. These genomes reflect the diversity of this complex ecosystem, with genus-level representatives for more than sixty per cent of the community. Meta-omic analysis revealed key populations involved in the degradation of organic matter, including bacteria whose genomes encode a previously undescribed fungal pathway for xylose degradation. Microbial and geochemical data highlight lineages that correlate with the production of greenhouse gases and indicate novel syntrophic relationships. Our findings link changing biogeochemistry to specific microbial lineages involved in carbon processing, and provide key information for predicting the effects of climate change on permafrost systems.
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