Active microbial biofilms in deep poor porous continental subsurface rocks

Area of Science:

• Deep subsurface microbiology
• Microbial ecology
• Geomicrobiology

Background:

• Deep continental subsurface environments are characterized by oligotrophic conditions and extremely low microbial metabolic rates.
• The energetic costs associated with biofilm formation and maintenance have led to the assumption that biofilms do not exist in nutrient-poor, porous subsurface rocks.

Purpose of the Study:

• To investigate the prokaryotic diversity, distribution, and potential existence of biofilms in the deep continental subsurface.
• To analyze samples from the Iberian Pyrite Belt (IPB) deep drilling project.

Main Methods:

• Application of fluorescence in situ hybridization (FISH) techniques.
• Utilized confocal laser scanning microscopy (CLSM) for high-resolution imaging.
• Analyzed microbial community structure and spatial organization in rock samples.

Main Results:

• Confirmed the presence of natural microbial biofilms at all depths investigated within the IPB subsurface.
• Observed the co-occurrence of both bacterial and archaeal species within these biofilms.
• Demonstrated that biofilms are not limited by oligotrophic conditions in this deep environment.

Conclusions:

• Microbial biofilms are a prevalent and established feature of the deep continental subsurface.
• The co-occurrence of bacteria and archaea suggests that multi-species biofilms represent a common lifestyle in these extreme environments.
• These findings challenge previous assumptions about microbial life in oligotrophic subsurface habitats.