Compositional differences in particle-associated and free-living microbial assemblages from an extreme deep-ocean...

Area of Science:

• Microbiology
• Deep-sea ecology
• Hadal zone research

Background:

• Hadal environments represent the deepest marine ecosystems, yet their microbial community composition remains largely unexplored.
• Understanding microbial life in these extreme environments is crucial for comprehending global biogeochemical cycles.
• Particle-associated and free-living microbial fractions may exhibit different ecological niches and adaptations.

Purpose of the Study:

• To characterize the phylogenetic diversity of microbial communities in the Puerto Rico Trench at 6000m depth.
• To compare the composition of particle-associated and free-living microbial fractions.
• To identify novel microbial groups and understand their ecological roles in hadal environments.

Main Methods:

• Small subunit ribosomal RNA gene sequencing was employed to analyze microbial DNA.
• Samples were collected from particle-associated (>3 µm) and free-living (3-0.22 µm) fractions.
• Phylogenetic analysis was performed to determine the diversity of Bacteria, Archaea, and Eukarya.

Main Results:

• Bacterial species richness was higher in particle-associated fractions, with significant compositional differences compared to free-living fractions.
• Distinct bacterial taxa were enriched in each fraction, including Rhodobacterales and Bacteroidetes in particle-associated, and Caulobacterales and Burkholderiales in free-living fractions.
• Eukaryotic communities were dominated by Basidiomycota Fungi and included diverse groups like Rhizaria, Excavata, Chromalveolata, and a novel clade of diplonemid flagellates.

Conclusions:

• Hadal microbial communities exhibit distinct partitioning between particle-associated and free-living fractions, particularly for bacteria.
• The Puerto Rico Trench harbors unique microbial lineages, including novel deep-sea flagellates.
• This research contributes to understanding microbial adaptation and ecological strategies in extreme deep-sea environments.