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Another chemolithotrophic metabolism missing in nature: sulfur comproportionation
Jan P Amend1,2, Heidi S Aronson1, Jennifer Macalady3
1Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
Environmental Microbiology
|March 12, 2020
Summary
Researchers predict a new microbial metabolism: sulfur comproportionation. This process, occurring in acidic, sulfide-rich environments, could provide sufficient energy for chemolithotrophic life, expanding our understanding of microbial energy strategies.
Area of Science:
- Microbial metabolism
- Geochemistry
- Biogeochemical cycles
Background:
- Chemotrophic microorganisms utilize oxidation-reduction (redox) reactions for energy.
- Gibbs energy change (ΔGr) calculations determine reaction favorability and energy yield.
- Existing microbial metabolisms do not fully account for energy in certain geochemical environments.
Discussion:
- A novel metabolism, sulfur comproportionation (3H2S + SO42- + 2H+ ⇌ 4S0 + 4H2O), is thermodynamically favorable under specific conditions.
- This reaction yields significant energy (~30-50 kJ mol-1) in acidic, high-sulfide, and high-sulfate environments across a range of temperatures.
- Alternative sulfur comproportionation pathways yielding thiosulfate or sulfite are less energetically favorable.
Key Insights:
- Sulfur comproportionation is predicted to be an exergonic process capable of supporting microbial life.
- This finding introduces a potentially significant, previously unrecognized chemolithotrophic metabolism.
- The energy yield is sufficient to support microbial cellular functions.
Outlook:
- Environments like sulfidic karst systems, hydrothermal vents, acid mine drainage sites, and crater lakes are prime locations to search for these novel microorganisms.
- Further research is needed to experimentally validate and characterize microbial sulfur comproportionators.
- This discovery could reshape our understanding of microbial roles in sulfur cycling and energy flow in extreme environments.
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