Novel Microbial Groups Drive Productivity in an Archean Iron Formation.

Area of Science:

• Geomicrobiology
• Deep Biosphere Research
• Microbial Ecology

Background:

• Deep subsurface microbial communities are isolated and face nutrient limitations.
• These limitations drive microbe-microbe interactions and biogeochemical cycling.
• Understanding these unique ecosystems is crucial for comprehending life's limits.

Purpose of the Study:

• To characterize microbial communities in low-temperature, chemically reduced brines.
• To investigate microbial metabolism and interactions in the Soudan Underground Mine.
• To identify novel microbial lineages and their roles in deep subsurface ecosystems.

Main Methods:

• Analysis of fractured rock aquifer brines from the Soudan Iron mine.
• Amplicon sequencing to determine microbial community composition.
• Metagenome assembly and metabolic reconstruction of recovered genomes.

Main Results:

• Low-diversity communities dominated by Firmicutes and Proteobacteria.
• Identification of novel microbial families and genera.
• Dominance of Wood-Ljungdahl and Calvin-Benson-Bassham carbon fixation pathways.
• Evidence for methanogenesis by *Methanolobus* and potential cryptic sulfur cycling.
• Microorganisms possess genes for multiple element cycling, indicating metabolic flexibility.

Conclusions:

• Deep subsurface brines harbor specialized microbial communities.
• Metabolic flexibility is a key adaptation for survival in isolated, nutrient-limited environments.
• These microbes play significant roles in deep biosphere biogeochemical cycles.