Unveiling active microbial processes in Earth's deepest seawater

Area of Science:

• Marine Microbiology
• Deep-Sea Ecology
• Biogeochemistry

Background:

• The hadal zone, Earth's deepest marine environment, is dominated by microorganisms.
• Extreme sampling challenges and low biomass have limited understanding of their in situ activities.
• Characterizing hadal microbial life is essential for comprehending deep-ocean ecosystems.

Purpose of the Study:

• To characterize the in situ activities and metabolic functions of hadal zone microorganisms.
• To identify specific microbial taxa and their biogeographic origins in the hadal environment.
• To elucidate the unique biogeochemical processes driven by hadal microbiomes.

Main Methods:

• In situ filtration of hadal seawater samples using human-occupied vehicles.
• DNA-protein co-extraction followed by metagenome-guided metaproteomic analysis.
• Proteomic quantification to distinguish active microbial taxa and their functions.

Main Results:

• Identification of 135,073 non-redundant active proteins, with over 95% being hadal-specific.
• Hadal microorganisms display a distinct metabolic regime, utilizing refractory organic matter and expanded electron acceptors (thiosulfate, heavy metals).
• Active viruses contribute to host adaptation via auxiliary metabolic genes, extending beyond simple 'Piggyback-the-Winner' dynamics.

Conclusions:

• Proteome-level evidence confirms unique microbial activities in the hadal zone.
• Hadal biogeochemical cycling is fundamentally distinct from the upper ocean, driven by specialized microbial metabolisms.
• Hadal microbiomes play a significant, underappreciated role in global ocean ecosystems.