Bathyarchaeia (formerly Bathyarchaeota or MCG), a widespread archaeal lineage, thrives in anoxic sediments worldwide, from marine and terrestrial environments to hydrothermal vents and hot springs. As metabolic generalists, they play a critical role in carbon cycling, degrading complex organic matter like proteins, lipids, and lignin, with capabilities for acetogenesis and potential methane metabolism. Their success across gradients of temperature and salinity is well-documented, yet their resilience to biological threats like viruses and abiotic stresses such as heavy metals and osmotic pressure remains poorly understood.
This research investigates three key adaptive mechanisms behind the ecological dominance of Bathyarchaeia. Analysis revealed 56 Bathyarchaeia-associated viral genomes, including four novel families, highlighting sophisticated virus-host dynamics with counter-defense strategies like atypical CRISPR-Cas systems. Genomic surveys of 318 Bathyarchaeia genomes showed arsenic resistance genes in 60% of them, linked to evolutionary responses during ancient geological shifts, such as the great oxygenation events and several Glaciations. For osmotic adaptation, comparative genomics of 404 genomes uncovered widespread systems for compatible solute synthesis (e.g., proline) and ion transport, with mangrove sediment meta-transcriptomes confirming enhanced expression of these pathways under high-salinity conditions. These findings underscore integrated genomic and evolutionary strategies of Bathyarchaeia, cementing their vital role in global sedimentary ecosystems.
 

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