Seasonal Regime Shift in the Viral Communities of a Permafrost Thaw Lake.

Catherine Girard,Warwick F Vincent,Alexander I Culley,Adrien Vigneron,Valérie Langlois

doi:10.3390/v12111204

Abstract

Permafrost thaw lakes including thermokarst lakes and ponds are ubiquitous features of Subarctic and Arctic landscapes and are hotspots of microbial activity. Input of terrestrial organic matter into the planktonic microbial loop of these lakes may greatly amplify global greenhouse gas emissions. This microbial loop, dominated in the summer by aerobic microorganisms including phototrophs, is radically different in the winter, when metabolic processes shift to the anaerobic degradation of organic matter. Little is known about the viruses that infect these microbes, despite evidence that viruses can control microbial populations and influence biogeochemical cycling in other systems. Here, we present the results of a metagenomics-based study of viruses in the larger than 0.22 µm fraction across two seasons (summer and winter) in a permafrost thaw lake in Subarctic Canada. We uncovered 351 viral populations (vOTUs) in the surface waters of this lake, with diversity significantly greater during the summer. We also identified and characterized several phage genomes and prophages, which were mostly present in the summer. Finally, we compared the viral community of this waterbody to other habitats and found unexpected similarities with distant bog lakes in North America.

Highlights

Permafrost covers approximately 17% of the globe’s land surface [1] and holds an estimated1330–1580 Pg of carbon [2]
The low number of viral operational taxonomic unit (vOTU) identified from our metagenomes (Supplementary Table S1) is due to these reads being acquired from water filtered onto 0.22 μm SterivexTM filters that were comprised mostly of cellular genomes
Of the 351 vOTUs detected in this study, the majority were found in the summer

Summary

Introduction

Permafrost covers approximately 17% of the globe’s land surface [1] and holds an estimated1330–1580 Pg of carbon [2]. Permafrost thawing can result in the release of stocks of ground carbon that are metabolized by microbes and decomposed into CH4 and CO2 [2,4,5]. It has been estimated that the contribution of permafrost thawing to the production of greenhouse gases alone to the atmosphere will result in an increase of global temperatures from 0.13–0.27 ◦ C by 2100 [2]. Carbon released from degraded permafrost is introduced into thaw lakes that include thermokarst lakes, small freshwater ecosystems formed from the thaw of ice-rich permafrost [6]. These waterbodies are ubiquitous features of continuous and discontinuous permafrost landscapes in northern latitudes [7]

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Conclusion