Surface sediment microbial communities remain viable, culturable, and metabolically active during sequential heating

Area of Science:

• Microbiology
• Geochemistry
• Environmental Science

Background:

• Marine sediments host diverse microbial life.
• Understanding microbial adaptation to deep subsurface conditions is crucial for studying the deep hot biosphere.

Purpose of the Study:

• To investigate the transition of temperate marine microbial communities to high-temperature subsurface conditions.
• To simulate deep burial effects on microbial community structure and function.

Main Methods:

• Sequential heating of estuarine sediment from 15°C to 90°C over 434 days.
• Monitoring cell counts, viability, and culturability.
• Analyzing microbial community composition using molecular methods.
• Measuring metabolic activity with radiolabeled substrates.

Main Results:

• Initial increase in total cell counts and culturability for specific groups (heterotrophs, sulfate reducers, methanogens) at moderate temperatures.
• Progressive decline in cell numbers and viability at higher temperatures (42°C to 90°C).
• Detection of culturable cells even at 90°C, capable of growing across a wide temperature range.
• Dominance of bacterial classes Clostridia (Caldicoprobacteraceae, Peptococcaceae) at elevated temperatures.
• Rapid metabolism of substrates at 90°C.

Conclusions:

• Temperate marine microbial communities can restructure functionally and compositionally under thermal stress.
• A cryptic thermophilic 'seed bank' likely facilitates adaptation to deep, hot environments.
• This process explains microbial inoculation and sustenance in the deep hot biosphere.