Ultra‐small and abundant: Candidate phyla radiation bacteria are potential catalysts of carbon transformation in a thermokarst lake ecosystem

• Published in: Limnology and Oceanography Letters
• Main Authors: Vigneron, Adrien, Cruaud, Perrine, Langlois, Valérie, Lovejoy, Connie, Culley, Alexander I., Vincent, Warwick F.
• Other Authors: Canada First Research Excellence Fund, Consiglio Nazionale delle Ricerche, Fonds Québécois de la Recherche sur la Nature et les Technologies, Natural Sciences and Engineering Research Council of Canada
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: permafrost; Subarctic; Thermokarst
• Online Access: http://dx.doi.org/10.1002/lol2.10132; https://onlinelibrary.wiley.com/doi/pdf/10.1002/lol2.10132; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/lol2.10132; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lol2.10132

Abstract The candidate phyla radiation (CPR) is a diverse group of uncultured bacterial lineages with poorly understood metabolic functions. CPR bacteria can represent a large proportion of the total planktonic microbial community in subarctic thermokarst lakes, but their functional roles remain unexplored. We applied sequential water filtration and metagenomic shotgun sequencing to a peatland permafrost thaw lake, and found high proportions of CPR bacteria in both summer and winter (> 40% of 16S rRNA reads in the 0.02–0.22 μ m pore‐size fraction). The metagenome‐assembled genomes of CPR bacteria representatives showed capacities to degrade and ferment permafrost‐ and peatland‐derived organic matter. Potential products of their metabolic activities included acetate, CO 2 , and hydrogen, implying a syntrophic relationship with other community members, including methanogens and methanotrophs. The results indicate biogeochemical interdependencies in organic matter utilization within thermokarst microbial communities, with CPR members playing a key intermediate role in carbon and methane cycling.