Redefining the Subsurface Biosphere: Characterization of Fungi Isolated From Energy-Limited Marine Deep Subsurface...

Area of Science:

• Marine microbiology
• Deep subsurface ecosystems
• Biogeochemical cycles

Background:

• Current deep subsurface ecosystem models primarily focus on bacterial and archaeal populations.
• Marine fungi have been studied for decades, but their role in the deep subsurface remains underexplored.
• Fungi possess unique metabolic capabilities to utilize previously non-bioavailable energy sources.

Purpose of the Study:

• To characterize metabolically active fungal populations in the deep marine subsurface.
• To assess the potential role of fungi in transforming energy reserves and influencing subsurface carbon cycling.
• To update living biomass estimates in marine ecosystems.

Main Methods:

• Sediment samples were collected from the South Pacific Gyre subsurface during Integrated Ocean Drilling Program Expedition 329.
• Anoxic and oxic sediment slurry enrichments were performed using varied organic carbon substrates and concentrations to isolate fungal strains.
• Nucleic acids from in situ cryopreserved sediments were analyzed to determine metabolically active and dormant fungal populations.

Main Results:

• Multiple fungal strains were successfully isolated from South Pacific Gyre sediments, demonstrating metabolic activity.
• Fungi were found to be adapted to the energy-limited deep subsurface environment.
• Two isolates were selected for further characterization based on their representation of the overall fungal community.

Conclusions:

• Fungi are metabolically active and integral members of the South Pacific Gyre sediment communities.
• The metabolic activity of these fungi has significant implications for subsurface organic carbon sources and energy budgets.
• These findings suggest a broader role for fungi in global biogeochemical cycles than previously recognized.