On the Possibility of Aerobic Methane Production by Pelagic Microbial Communities of the Laptev Sea

O S Samylina,A A Grinko,E V Yakushev,I I Rusanov,N V Pimenov,I P Semiletov,T A Kanapatskiy,A Yu Merkel,E E Zakharova,I Yu Tarnovetskii

doi:10.1134/s0026261721020119

Abstract

—The taxonomic diversity and metabolic activity of microbial communities in the Laptev Sea water column above and outside the methane seep field were studied. The concentrations of dissolved methane in the water column at both stations were comparable until the depth of the pycnocline (25 m). At this depth, local methane maxima were recorded, with the highest concentration (116 nM CH4) found at the station outside the methane seep field. Results of the 16S rRNA gene sequencing and measurements of the rates of hydrogenotrophic methanogenesis indicated the absence of methanogenesis caused by the methanogenic archaea in the pycnocline and in other horizons of the water column. The 16S rRNA-based analysis of microbial phylogenetic diversity, as well as radiotracer analysis of the rates of primary production (PP), dark CO2 assimilation (DCA), and methane oxidation (MO), indicated the functioning of a diverse community of pelagic microorganisms capable of transforming a wide range of organic compounds under oligotrophic conditions of the Arctic basin. Hydrochemical prerequisites and possible microbial agents of aerobic methane production via demethylation of methylphosphonate and decomposition of dimethylsulfoniopropionate using dissolved organic matter synthesized in the PP, DCA, and MO processes are discussed.

Highlights

The methane cycle is an important component of the carbon biogeochemical cycle in the ocean
Unidentified members of the family Nitrincolaceae were related to uncultured clones of marine gammaproteobacteria Arctic96B-16 and Ant4D3. It was earlier found for the central part of the Arctic Ocean that the subsurface methane concentrations were close to the values in equilibrium with the atmosphere (3.5−4 nM) in the Atlantic-derived waters, while it reached 5−7 nM in Pacific-derived waters, which in the second case was associated with the aerobic biological production of methane by pelagic communities (Damm et al, 2010)
Methane concentrations in the upper horizons of the water column at the studied stations above the methane seep (AMK736045) and at a distance from it (AMK73-6053) had comparable values and were in the range of 25.9− 50.4 nM (Table 1), which indicates a significant oversaturation of surface waters of the studied region with methane

Summary

Introduction

The methane cycle is an important component of the carbon biogeochemical cycle in the ocean. Recent studies revealed methane production by diverse phytoplanktonic microorganisms: cyanobacteria, coccolithophorids and other haptophytes, diatoms (see review by Bižić et al, 2020 and references therein) In this case, the issue is associated not with previously known metabolic pathways (MPn demethylation or production of hydrogen by nitrogenase and hydrogenases, with its subsequent utilization in hydrogenotrophic methanogenesis), but with an unknown mechanism of CO2 conversion to methane linked to the basic metabolism of oxygenic phototrophs. In order to assess the possible agents of microbial methane production under oxic conditions of the Laptev Sea water column, comparative study of the hydrochemical parameters was carried out in the present work, as well as determination of the taxonomic diversity and functional activity of pelagic microbial communities at stations located both above and outside the field of methane seeps

Methods

Results

Conclusion