Ammonia oxidizing archaea play a central role in the biogeochemical cycling of nitrogen in benthic sediments, at the interface between pelagic and subsurface ecosystems. However, our understanding of their niche separation and of the processes controlling their population structure in hadal and abyssal surface sediments is still limited. Here, we reconstructed 47 AOA metagenome-assembled genomes (MAGs) of varying quality from surface sediments of the Atacama and Kermadec trench systems. They formed deep-sea specific groups within the family Nitrosopumilaceae and were assigned to six amoA gene-based clades. MAGs from different clades had distinct distribution patterns along oxygen-ammonium countergradients in surface sediments. At the species level, MAGs thus seemed to form different ecotypes and follow deterministic niche-based distributions. In contrast, intraspecific population structure, defined by patterns of Single Nucleotide Variants (SNV), seemed to reflect more complex contributions of both deterministic and stochastic processes.
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Lois Maignien (université de Brest)