"Sifarchaeota," a Novel Asgard Phylum from Costa Rican Sediment Capable of Polysaccharide Degradation and Anaerobic Methylotrophy.

The Asgard superphylum is a deeply branching monophyletic group of Archaea, recently described as some of the closest relatives of the eukaryotic ancestor. The wide application of genomic analyses from metagenome sequencing has established six distinct phyla, whose genomes encode diverse metabolic capacities and which play important biogeochemical and ecological roles in marine sediments. Here, we describe two metagenome-assembled genomes (MAGs) recovered from deep marine sediments off the Costa Rica margin, defining a novel lineage phylogenetically married to "Candidatus Thorarchaeota"; as such, we propose the name "Sifarchaeota" for this phylum. The two Sifarchaeota MAGs encode an anaerobic pathway for methylotrophy enabling the utilization of C1 to C3 compounds (methanol and methylamines) to synthesize acetyl coenzyme A (acetyl-CoA). The MAGs showed a remarkable saccharolytic capabilities compared to other Asgard lineages and encoded diverse classes of carbohydrate active enzymes (CAZymes) targeting different mono-, di-, and oligosaccharides. Comparative genomic analysis based on the full metabolic profiles of different Asgard lineages revealed the close relation between Sifarchaeota and "Candidatus Odinarchaeota" MAGs, which suggested similar metabolic potentials and ecological roles. Furthermore, we identified multiple HGT events from different bacterial donors within Sifarchaeota MAGs, which hypothetically expanded Sifarchaeota capacities for substrate utilization, energy production, and niche adaptation.IMPORTANCE The exploration of deep marine sediments has unearthed many new lineages of microbes. The finding of this novel phylum of Asgard archaea is important, since understanding the diversity and evolution of Asgard archaea may inform also about the evolution of eukaryotic cells. The comparison of metabolic potentials of the Asgard archaea can help inform about selective pressures the lineages have faced during evolution.