Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Earth and Environmental Systems Institute, University Park, Pennsylvania, USA.
Geobiology. 2022 Mar;20(2):271-291. doi: 10.1111/gbi.12474. Epub 2021 Oct 11.
Oxidative weathering of pyrite plays an important role in the biogeochemical cycling of Fe and S in terrestrial environments. While the mechanism and occurrence of biologically accelerated pyrite oxidation under acidic conditions are well established, much less is known about microbially mediated pyrite oxidation at circumneutral pH. Recent work (Percak-Dennett et al., 2017, Geobiology, 15, 690) has demonstrated the ability of aerobic chemolithotrophic microorganisms to accelerate pyrite oxidation at circumneutral pH and proposed two mechanistic models by which this phenomenon might occur. Here, we assess the potential relevance of aerobic microbially catalyzed circumneutral pH pyrite oxidation in relation to subsurface shale weathering at Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) in Pennsylvania, USA. Specimen pyrite mixed with native shale was incubated in groundwater for 3 months at the inferred depth of in situ pyrite oxidation. The colonized materials were used as an inoculum for pyrite-oxidizing enrichment cultures. Microbial activity accelerated the release of sulfate across all conditions. 16S rRNA gene sequencing and metagenomic analysis revealed the dominance of a putative chemolithoautotrophic sulfur-oxidizing bacterium from the genus Thiobacillus in the enrichment cultures. Previously proposed models for aerobic microbial pyrite oxidation were assessed in terms of physical constraints, enrichment culture geochemistry, and metagenomic analysis. Although we conclude that subsurface pyrite oxidation at SSCHZO is largely abiotic, this work nonetheless yields new insight into the potential pathways by which aerobic microorganisms may accelerate pyrite oxidation at circumneutral pH. We propose a new "direct sulfur oxidation" pathway, whereby sulfhydryl-bearing outer membrane proteins mediate oxidation of pyrite surfaces through a persulfide intermediate, analogous to previously proposed mechanisms for direct microbial oxidation of elemental sulfur. The action of this and other direct microbial pyrite oxidation pathways have major implications for controls on pyrite weathering rates in circumneutral pH sedimentary environments where pore throat sizes permit widespread access of microorganisms to pyrite surfaces.
黄铁矿的氧化风化在陆地环境中铁和硫的生物地球化学循环中起着重要作用。虽然在酸性条件下生物加速黄铁矿氧化的机制和发生已经得到很好的证实，但在近中性 pH 值条件下微生物介导的黄铁矿氧化过程却知之甚少。最近的研究（Percak-Dennett 等人，2017 年，《地球生物学》，15，690）已经证明了好氧化能自养微生物在近中性 pH 值条件下加速黄铁矿氧化的能力，并提出了两种可能发生这种现象的机制模型。在这里，我们评估了好氧微生物催化近中性 pH 值黄铁矿氧化与美国宾夕法尼亚州萨斯奎哈纳页岩丘陵关键带观测站（Susquehanna Shale Hills Critical Zone Observatory，SSHCZO）地下页岩风化的潜在相关性。将与原生页岩混合的标本黄铁矿在地下水中孵育 3 个月，模拟原位黄铁矿氧化的推测深度。用这些被微生物定殖的材料作为黄铁矿氧化富集培养物的接种物。微生物活性加速了所有条件下硫酸盐的释放。16S rRNA 基因测序和宏基因组分析显示，在富集培养物中，一种来自硫杆菌属的假定化能自养硫氧化细菌占主导地位。先前提出的好氧微生物黄铁矿氧化模型从物理限制、富集培养物地球化学和宏基因组分析方面进行了评估。尽管我们得出结论，SSCHZO 地下黄铁矿氧化主要是无生命的，但这项工作为有氧微生物在近中性 pH 值下加速黄铁矿氧化的潜在途径提供了新的见解。我们提出了一种新的“直接硫氧化”途径，其中带有巯基的外膜蛋白通过过硫酸盐中间体介导黄铁矿表面的氧化，类似于先前提出的直接微生物氧化元素硫的机制。这种和其他直接微生物黄铁矿氧化途径的作用对近中性 pH 值沉积环境中黄铁矿风化速率的控制有重大影响，在这些环境中，孔隙喉道的大小允许微生物广泛接触黄铁矿表面。
