Deep terrestrial indigenous microbial community dominated by Candidatus Frackibacter

Area of Science:

• Geomicrobiology
• Astrobiology
• Environmental Science

Background:

• Deep subsurface microbial communities are crucial for understanding Earth's biogeochemistry and the search for extraterrestrial life.
• The Kidd Creek Observatory provides a unique environment to study ancient microbial ecosystems with residence times exceeding one billion years.

Purpose of the Study:

• To characterize the microbial communities within the Kidd Creek Observatory subsurface fracture water system.
• To investigate the metabolic potential and origins of dominant microbial species in this ancient environment.

Main Methods:

• 16S rRNA gene sequencing to identify microbial taxa.
• Analysis of phospholipid fatty acid (PLFA) δ¹³C values to infer carbon sources.
• Bioinformatic analysis for putative functional predictions of microbial communities.

Main Results:

• Microbial communities isolated from the mine environment were dominated by *Candidatus* Frackibacter, a putatively anaerobic and halophilic bacterium from the *Halobacteroidaceae* family.
• Biosamplers and biofilms exposed to the mine environment harbored aerobic *Sphingomonas* taxa.
• Evidence suggests *Candidatus* Frackibacter utilizes carbon from ancient, carbon-rich rock layers, indicating its presence in diverse deep saline groundwaters.

Conclusions:

• *Candidatus* Frackibacter is indigenous to deep, saline groundwaters in carbon-rich rock environments, not exclusive to hydraulically fractured basins.
• This research enhances our comprehension of deep subsurface microbial ecology and its implications for astrobiology.
• The study highlights the adaptability and ancient origins of microbial life in extreme subterranean ecosystems.