Power limits for microbial life.

Area of Science:

• Astrobiology and Geomicrobiology
• Understanding the energetic limits of life in extreme environments

Background:

• The minimum energy flux required for life's viability is crucial for understanding life's origins and extent.
• Directly measuring power limits for life is challenging, necessitating indirect modeling approaches.

Purpose of the Study:

• To quantify the minimum energy flux required to sustain microorganisms in an ultralow-energy marine sedimentary environment.
• To establish a link between power consumption and microbial biomass in such settings.

Main Methods:

• Application of a bioenergetic model to data from IODP Site U1370 in the South Pacific Gyre.
• Calculation of particular organic carbon (POC) degradation rates using a continuum model.
• Computation of Gibbs energies using geochemical data as a function of sediment depth.

Main Results:

• Power supply in the studied environment ranges from approximately 10^-12 to 10^-16 W cm^-3.
• Microbial biomass (cells cm^-3) is directly correlated with power consumption.
• A maintenance power of 190 zW cell^-1 effectively captures cell density, significantly lower than previously reported values.

Conclusions:

• Microorganisms at Site U1370 require an average of 50-3500 zW cell^-1, with most below ~300 zW cell^-1.
• The absolute minimum power requirement for a single viable cell is estimated to be around 1 zW cell^-1.
• This research provides critical insights into the energetic constraints on life in extreme, energy-limited environments.