Truncated denitrifiers dominate the denitrification pathway in tundra soil metagenomes

In contrast to earlier assumptions, there is now mounting evidence for the role of tundra soils as important sources of the greenhouse gas nitrous oxide (N₂O). However, the microorganisms involved in the cycling of N₂O in these soils remain largely uncharacterized. In this study, we manually binned and curated 541 metagenome-assembled genomes (MAGs) from tundra soils in northern Finland.

We then searched for MAGs encoding enzymes involved in denitrification, the main biotic process driving N₂O emissions. Denitrifying communities were dominated by poorly characterized taxa with truncated denitrification pathways, i.e. lacking one or more denitrification genes. Among these, MAGs with the metabolic potential to produce N₂O comprised the most diverse functional group.

Re-analysis of a previously published metagenomic dataset from soils in northern Sweden supported these results, suggesting that truncated denitrifiers are dominant throughout the tundra biome.