Unveiling the life of archaea in sediments: Diversity, metabolic potentials, and ecological roles

The domain Archaea was initially characterized as extremophiles upon its proposal. Recent significant discoveries have redrawn our views of archaeal biology, encompassing the identification of mesophilic archaeal groups, the expansion of archaeal diversity and metabolic capabilities, and the elucidation of evolutionary relationships among archaea, bacteria, and eukaryotes. Archaea are ubiquitous and constitute a substantial fraction of the microbial biomass within sediments. Therefore, comprehending their ecological roles is paramount for understanding their contributions to global geochemical cycles. In this review, we summarize the diversity of archaea across various sediment ecosystems, from terrestrial inland to deep-sea environments, utilizing representative genomes supported by the Genome Taxonomy Database, which encompasses habitats such as hot springs, salt lakes, freshwater lakes, rivers, mangroves, estuaries, coastal regions, seafloor sediments, cold seeps, and hydrothermal vents. Furthermore, we integrate analyses of representative genomes with recent studies to highlight the metabolic potentials, novel enzymatic functions, and significant discoveries related to the carbon, nitrogen, and sulfur cycles across different archaeal lineages. Finally, we discuss recent research hotspots and achievements in archaeal studies, while projecting future exploration directions. The expanding diversity and metabolic capacities of archaea have broadened our perspective on the tree of life and underscored their critical impacts on ecosystems.