Novel metagenome-assembled genomes involved in the nitrogen cycle from a Pacific oxygen minimum zone

Oxygen minimum zones (OMZs) are unique marine regions where broad redox gradients stimulate biogeochemical cycles. Despite the important and unique role of OMZ microbes in these cycles, they are less characterized than microbes from the oxic ocean. Here we recovered 39 high- and medium-quality metagenome-assembled genomes (MAGs) from the Eastern Tropical South Pacific OMZ. More than half of these MAGs were not represented at the species level among 2631 MAGs from global marine datasets. OMZ MAGs were dominated by denitrifiers catalyzing nitrogen loss and especially MAGs with partial denitrification metabolism. A novel bacterial genome with nitrate-reducing potential could only be assigned to the phylum level. A Marine-Group II archaeon was found to be a versatile denitrifier, with the potential capability to respire multiple nitrogen compounds including N(2)O. The newly discovered denitrifying MAGs will improve our understanding of microbial adaptation strategies and the evolution of denitrification in the tree of life.