Life at the frozen limit: Microbial carbon metabolism across a Late Pleistocene permafrost chronosequence

Frontiers in Microbiology
By: , and 



Permafrost is an extreme habitat yet it hosts microbial populations that remain active over millennia. Using permafrost collected from a Pleistocene chronosequence (19 to 33 ka), we hypothesized that the functional genetic potential of microbial communities in permafrost would reflect microbial strategies to metabolize permafrost soluble organic matter (OM) in situ over geologic time. We also hypothesized that changes in the metagenome across the chronosequence would correlate with shifts in carbon chemistry, permafrost age, and paleoclimate at the time of permafrost formation. We combined high-resolution characterization of water-soluble OM by Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS), quantification of organic anions in permafrost water extracts, and metagenomic sequencing to better understand the relationships between the molecular-level composition of potentially bioavailable OM, the microbial community, and permafrost age. Both age and paleoclimate had marked effects on both the molecular composition of dissolved OM and the microbial community. The relative abundance of genes associated with hydrogenotrophic methanogenesis, carbohydrate active enzyme families, nominal oxidation state of carbon (NOSC), and number of identifiable molecular formulae significantly decreased with increasing age. In contrast, genes associated with fermentation of short chain fatty acids (SCFAs), the concentration of SCFAs and ammonium all significantly increased with age. We present a conceptual model of microbial metabolism in permafrost based on fermentation of OM and the buildup of organic acids that helps to explain the unique chemistry of ancient permafrost soils. These findings imply long-term in situ microbial turnover of ancient permafrost OM and that this pooled biolabile OM could prime ancient permafrost soils for a larger and more rapid microbial response to thaw compared to younger permafrost soils.

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Publication type Article
Publication Subtype Journal Article
Title Life at the frozen limit: Microbial carbon metabolism across a Late Pleistocene permafrost chronosequence
Series title Frontiers in Microbiology
DOI 10.3389/fmicb.2020.01753
Volume 11
Year Published 2020
Language English
Publisher Frontiers Media
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 1753, 15 p.
Country United States
State Alaska
City Fairbanks
Other Geospatial Cold Regions Research and Engineering Laboratory
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