Modeled energetics of bacterial communities in ancient subzero brines

Area of Science:

• Geomicrobiology
• Permafrost Science
• Astrobiology

Background:

• Cryopeg brines are ancient, isolated hypersaline water bodies found in subzero permafrost.
• The Utqiaġvik, Alaska cryopeg system, dating back to the late Pleistocene, contains high organic carbon and bacterial densities.
• The energetic basis for supporting these extreme ecosystems remains poorly understood.

Purpose of the Study:

• To investigate the energetics of the Utqiaġvik cryopeg brine ecosystem.
• To estimate microbial metabolic rates in a subzero, hypersaline environment.
• To model the organic carbon cycle and microbial community growth trajectories.

Main Methods:

• Estimated initial organic carbon quantities using literature data and archived borehole samples.
• Calculated bounds for cell-specific metabolic rates based on bacterial growth trajectories.
• Developed and applied an organic carbon cycle model to borehole data, incorporating enzymatic conversion rates and dissolved inorganic carbon/nitrogen measurements.

Main Results:

• The study provides the first community estimates of metabolic rates in subzero hypersaline environments.
• Model simulations successfully reconstructed microbial growth, predicting current cell densities and organic carbon content.
• Cell-specific metabolic rates were found to be relatively high compared to marine sediments, attributed to energy investment in extracellular enzymes and polysaccharides.

Conclusions:

• The Utqiaġvik cryopeg ecosystem's high microbial metabolic rates are supported by efficient organic carbon cycling and cryoprotective strategies.
• These findings offer insights into microbial life in isolated, extreme environments on Earth.
• The study has implications for understanding potential life in extraterrestrial ice-bound brines, such as on Europa, Enceladus, and Mars.