Radiolytic support for oxidative metabolism in an ancient subsurface brine system

Area of Science:

• * Astrobiology and Geomicrobiology: Investigating life in extreme subsurface environments.

Background:

• * Deep subsurface brine environments, isolated for millions to billions of years, present unique challenges and opportunities for microbial habitability.
• * Limited understanding exists regarding microbial communities in these low-biomass, hypersaline, and radiolytically active systems.

Purpose of the Study:

• * To characterize the taxonomic and metabolic potential of microbial life in a deep, isolated brine from the Moab Khotsong mine.
• * To assess the habitability of such extreme environments by analyzing microbial energy acquisition and survival strategies.

Main Methods:

• * Single-cell genome amplification and sequencing of 95 genomes from a low-biomass brine sample.
• * Taxonomic and functional annotation of obtained genomes to infer metabolic capabilities.
• * Comparison of microbial communities with surrounding mine water and aquifer samples.

Main Results:

• * The dominant microbial families identified were Halomondaceae (58%), Microbacteriaceae (24%), and Idiomarinaceae (8%), distinct from other mine water samples.
• * Metabolic pathways indicated capabilities for aerobic heterotrophy, fermentation, denitrification, and thiosulfate oxidation.
• * Microbes possessed pathways for complex organic degradation, biosynthesis, and motility, suggesting adaptation to the extreme conditions.

Conclusions:

• * Subsurface brines with high radionuclide concentrations can support microbial life fueled by radiolytically generated substrates like oxygen.
• * These environments are potentially habitable and redox-sustainable over geological timescales (thousands to billions of years).
• * The findings expand our understanding of life's limits in extreme subsurface ecosystems.