Methylotrophic Communities Associated with a Greenland Ice Sheet Methane Release Hotspot

Abstract

Subglacial environments provide conditions suitable for the microbial production of methane, an important greenhouse gas, which can be released from beneath the ice as a result of glacial melting. High gaseous methane emissions have recently been discovered at Russell Glacier, an outlet of the southwestern margin of the Greenland Ice Sheet, acting not only as a potential climate amplifier but also as a substrate for methane consuming microorganisms. Here, we describe the composition of the microbial assemblage exported in meltwater from the methane release hotspot at Russell Glacier and its changes over the melt season and as it travels downstream. We found that a substantial part (relative abundance 27.2% across the whole dataset) of the exported assemblage was made up of methylotrophs and that the relative abundance of methylotrophs increased as the melt season progressed, likely due to the seasonal development of the glacial drainage system. The methylotrophs were dominated by representatives of type I methanotrophs from the Gammaproteobacteria; however, their relative abundance decreased with increasing distance from the ice margin at the expense of type II methanotrophs and/or methylotrophs from the Alphaproteobacteria and Betaproteobacteria. Our results show that subglacial methane release hotspot sites can be colonized by microorganisms that can potentially reduce methane emissions.

Understanding microbial sourcing in Greenland subglacial runoff

“…How widespread these conditions are beneath the ice sheet, however, is unclear, but very similar methane-oxidizing populations have been reported for example in the (micro)oxic and methane-rich water and sediment layers of subglacial lakes in Antarctica (Davis et al, 2023;Achberger et al, 2016). Near identical methanotrophic populations were also overrepresented in small methane-rich subglacial outflows of the same GrIS sector throughout the 2012, 2018 and 2019 melt seasons (Dieser et al, 2014;Znamínko et al, 2023). Unlike for the LG river here, however, these relatively smaller outflows drain much smaller areas of the bed constrained near the ice margin and might not be representative of ice sheet environments at large (Hawkings et al, 2021b).…”

“…However, major clades of both methanotrophic and methanogenic populations from subglacial outflows in the same GrIS sector have been described previously (Vrbická et al, 2022;Lamarche-Gagnon et al, 2019;Dieser et al, 2014;Stibal et al, 2012;Znamínko et al, 2023). Based on these previous reports, we herein define putative methanotroph bacterial populations as OTUs of the genera Methylobacter and Crenothrix (Znamínko et al, 2023), and putative methanogen populations as OTUs of the orders Methanobacteriales, Methanomicrobiales, Methanosarcinales (Lamarche-Gagnon et al, 2019).…”