Epilithic Microbial Community Functionality in Deep Oligotrophic Continental Bedrock

Area of Science:

• Geomicrobiology
• Deep Biosphere Research
• Microbial Ecology

Background:

• The deep terrestrial biosphere harbors extensive rock surface communities, yet research has primarily focused on planktic microbes.
• Understanding sessile microbial life in deep subsurface environments is crucial for comprehending Earth's biosphere.

Purpose of the Study:

• To investigate microbial communities colonizing mica schist in the deep subsurface.
• To characterize the structure, diversity, and metabolic potential of sessile biofilms.

Main Methods:

• Enrichment of deep subsurface microbial communities on mica schist in microcosms.
• Scanning electron microscopy (SEM) for biofilm visualization and morphology analysis.
• Amplicon sequencing and metagenome-assembled genomes (MAGs) for community composition and metabolic profiling.

Main Results:

• Diverse microbial morphologies and attachment strategies observed on mica schist surfaces.
• Dominance of genera such as *Pseudomonas*, *Desulfosporosinus*, *Hydrogenophaga*, and *Brevundimonas* after prolonged incubation.
• Identification of genes for biofilm formation and diverse metabolic pathways, including organic carbon oxidation and arsenate/selenate reduction.

Conclusions:

• Deep subsurface microbial communities form complex biofilms on rock surfaces, demonstrating significant adaptability to oligotrophic conditions.
• The interaction between microbes and rock surfaces is vital for sustaining life in the deep, anoxic crystalline bedrock environment.
• These sessile communities possess versatile metabolic capabilities, enabling them to utilize various energy and carbon sources.