Reductive biomining of pyrite by methanogens

Area of Science:

• Geochemistry
• Microbiology
• Biogeochemistry

Background:

• Pyrite (FeS2) is a common iron sulfide mineral.
• FeS2 was previously considered a nutrient sink in anoxic environments.
• Anaerobic methanogens are microorganisms that produce methane.

Purpose of the Study:

• To investigate the role of anaerobic methanogens in the reductive dissolution of pyrite.
• To understand how FeS2 reduction impacts iron and sulfur bioavailability for microbial assimilation.

Main Methods:

• Studied extracellular electron transfer from methanogens to FeS2.
• Analyzed the multistep reduction process of FeS2.
• Characterized the formation and dissolution of intermediate mineral phases like pyrrhotite (Fe1-xS).
• Investigated the complexation of iron and sulfide into soluble iron-sulfur clusters (nFeS).

Main Results:

• Methanogens reductively dissolve FeS2 through direct mineral contact.
• FeS2 reduction generates aqueous sulfide (HS-) and pyrrhotite (Fe1-xS).
• Pyrrhotite dissolution releases Fe(II)aq, which complexes with HS-aq to form bioavailable nFeS clusters.
• Microbial cells assimilate nFeS clusters to meet iron and sulfur nutritional requirements.

Conclusions:

• Reductive dissolution of FeS2 by methanogens makes iron and sulfur bioavailable.
• This process is crucial for element cycling in anoxic habitats.
• Findings have implications for understanding ancient and modern biogeochemical cycles.