Abstract
The formation and fate of pyrite (FeS2) modulates global iron, sulfur, carbon, and oxygen biogeochemical cycles and has done so since early in Earth’s geological history. A longstanding paradigm is that FeS2 is stable at low temperature and is unavailable to microorganisms in the absence of oxygen and oxidative weathering. Here, we show that methanogens can catalyze the reductive dissolution of FeS2 at low temperature (≤38 °C) and utilize dissolution products to meet cellular iron and sulfur demands associated with the biosynthesis of simple and complex co-factors. Direct access to FeS2 is required to catalyze its reduction and/or to assimilate iron monosulfide that likely forms through coupled reductive dissolution and precipitation, consistent with close associations observed between cells and FeS2. These findings demonstrate that FeS2 is bioavailable to anaerobic methanogens and can be mobilized in low temperature anoxic environments. Given that methanogens evolved at least 3.46 Gya, these data indicate that the microbial contribution to the iron and sulfur cycles in ancient and contemporary anoxic environments may be more complex and robust than previously recognized, with impacts on the sources and sinks of iron and sulfur and other bio-essential and thiophilic elements such as nickel and cobalt.
Highlights
Pyrite (FeS2) is the most abundant sulfide mineral in Earth’s crust and its formation and fate are key controls on the biogeochemical cycles of iron (Fe), sulfur (S), carbon, and oxygen (O2) [1]
Cultivation of M. voltae and M. barkeri, when provided with formate or methanol and acetate as the methanogenesis substrates, respectively, resulted in significant cell and CH4 production in cultures containing nanoparticulate FeS2 or canonical forms of Fe and S but were not observed in cultures unamended with Fe or S (Fig. 1a–d and Extended Data File 1)
Growth of both M. voltae and M. barkeri was observed with powdered specimen FeS2 as the sole Fe and S source (SOM Fig. S3)
Summary
Pyrite (FeS2) is the most abundant sulfide mineral in Earth’s crust and its formation and fate are key controls on the biogeochemical cycles of iron (Fe), sulfur (S), carbon, and oxygen (O2) [1]. The specific role of sulfide minerals, such as FeS2, in these cycles has changed drastically over geological time [2, 3]. Prior to the advent of oxygenic photosynthesis and the gradual accumulation of O2 ~2.4 Gya (as reviewed in [5, 6]), biotic and abiotic oxidative weathering of FeS2 with O2, the primary driver of sulfate (SO42−) input into oceans [7], was of minimal importance [3, 6, 8, 9]. Reduction of FeS2 has only been demonstrated at high temperature (>90 °C) in abiotic laboratory reactors containing artificially high
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