Reductive biomining of pyrite by methanogens.

Pyrite (FeS) is the most abundant iron sulfide mineral in Earth's crust. Until recently, FeS has been considered a sink for iron (Fe) and sulfur (S) at low temperature in the absence of oxygen or oxidative weathering, making these elements unavailable to biology. However, anaerobic methanogens can transfer electrons extracellularly to reduce FeS via direct contact with the mineral. Reduction of FeS occurs through a multistep process that generates aqueous sulfide (HS) and FeS-associated pyrrhotite (FeS). Subsequent dissolution of FeS provides Fe(II), but not HS, that rapidly complexes with HS generated from FeS reduction to form soluble iron sulfur clusters [nFeS]. Cells assimilate nFeS to meet Fe/S nutritional demands by mobilizing and hyperaccumulating Fe and S from FeS. As such, reductive dissolution of FeS by methanogens has important implications for element cycling in anoxic habitats, both today and in the geologic past.