Microbial ecosystems and ecological driving forces in the deepest ocean sediments

Area of Science:

• Marine Biology
• Microbial Ecology
• Oceanography

Background:

• The hadal zone, Earth's deepest oceanic realm (6-11 km), presents extreme conditions and has been historically difficult to explore.
• Understanding microbial life in these environments is crucial for comprehending deep-sea ecosystems.

Purpose of the Study:

• To systematically explore the microbial diversity and ecological drivers in the hadal zone.
• To analyze the genomic adaptations of microbes to extreme hadal conditions.

Main Methods:

• Collection of 1,648 sediment samples from the Mariana Trench, Yap Trench, and Philippine Basin.
• Generation of a 92-Tbp dataset using metagenomic and 16S rRNA gene amplicon sequencing (MEER dataset).
• Analysis of ecological drivers, including neutral drift, homogeneous selection (HoS), and dispersal limitation (DL).

Main Results:

• Discovery of 7,564 microbial species, with 89.4% being previously unreported, indicating significant taxonomic novelty.
• Homogeneous selection (50.5%) and dispersal limitation (43.8%) were identified as dominant ecological drivers, with minimal role for neutral drift.
• Homogeneous selection favored streamlined genomes with functions for oligotrophic and high-pressure adaptation (e.g., aromatic compound utilization, antioxidation).
• Dispersal limitation promoted versatile metabolism and larger genomes.

Conclusions:

• Environmental factors, particularly homogeneous selection and dispersal limitation, are primary drivers of high microbial taxonomic novelty in the hadal zone.
• Microbial genomes in the hadal zone exhibit specific adaptations for survival in extreme oligotrophic and high-pressure conditions.
• This study advances the understanding of ecological mechanisms governing microbial ecosystems in Earth's deepest oceanic environments.