Fungi and macroaggregation in deep-sea sediments.

Area of Science:

• Marine biology
• Deep-sea ecology
• Mycology

Background:

• Fungal presence in terrestrial soils is well-documented, but deep-sea sediment fungi remain largely unstudied.
• Previous research indicated low fungal abundance in deep-sea sediments, hindering understanding of their ecological roles.
• Fungal hyphae have been detected in deep-sea sediments, but their low abundance suggests cryptic habitats.

Purpose of the Study:

• To investigate the cryptic habitats of fungi in deep-sea sediments.
• To quantify fungal biomass in deep-sea sediments and explore factors affecting detection.
• To understand the role of deep-sea fungi in aggregate formation and carbon cycling.

Main Methods:

• Fungal biomass carbon was estimated using direct microscopic detection of fungal mycelia in deep-sea sediment cores.
• Sediment samples were treated with ethylenediamine tetra-acetic acid (EDTA) to facilitate aggregate breakdown and fungal detection.
• Experimental studies cultured deep-sea and terrestrial fungi under simulated deep-sea conditions (200 bar, 5°C).

Main Results:

• EDTA treatment significantly increased fungal detection and biomass compared to untreated samples, revealing hyphae within macroaggregates.
• Fungal hyphae were observed actively forming aggregates by accreting sediment particles, incorporating humic material, carbohydrates, and proteins.
• Both deep-sea and terrestrial fungal isolates demonstrated growth capabilities under high pressure and low temperature conditions.

Conclusions:

• Fungi in deep-sea sediments are often cryptic within macroaggregates, explaining their previously underestimated abundance.
• Deep-sea fungi likely play a significant role in forming humic aggregates, similar to terrestrial fungi.
• The contribution of fungal-mediated aggregate formation to deep-sea carbon sequestration and food webs warrants further investigation.