Microbiomes in the Challenger Deep slope and bottom-axis sediments.

Area of Science:

• Deep-sea microbiology
• Oceanography
• Geochemistry

Background:

• Hadal trenches represent the ocean's deepest, most remote environments.
• The Challenger Deep, at 11 km, is challenging to sample, limiting exploration.
• Organic matter and heavy metals accumulate uniquely in the Challenger Deep's topography.

Purpose of the Study:

• To investigate in situ microbial communities in Challenger Deep sediments.
• To understand the diversity and metabolic capabilities of hadal microbes.
• To explore microbially-mediated elemental cycling in extreme deep-sea environments.

Main Methods:

• Sediment collection from Challenger Deep slopes and bottom-axis.
• Analysis of 37 metagenomes yielding 586 metagenome-assembled genomes.
• Metagenomic and metatranscriptomic analyses of microbial communities.

Main Results:

• Distinct microbial diversity and metabolic capacities were observed between bottom-axis and slope sites.
• 26% of prokaryotic 16S rDNA reads were novel, increasing with depth.
• Evidence for arsenate reduction/biotransformation and anaerobic ammonia oxidation was found, with variations across the trench.

Conclusions:

• Microbial communities in the Challenger Deep are adapted to extreme conditions with unique metabolic potentials.
• Hadal sediment microbial life plays a role in elemental cycling, including arsenic and nitrogen transformations.
• Differences in microbial processes across the trench topography highlight the heterogeneity of hadal ecosystems.