Pyrite, or iron disulfide, is the most common sulfide mineral on the Earth’s surface and is widespread through the geological record. Because sulfides are mainly produced by sulfate-reducing bacteria (SRB) in modern sedimentary environments, microorganisms are assumed to drive the formation of iron sulfides, in particular, pyrite. However, the exact role played by microorganisms in pyrite formation remains unclear and, to date, the precipitation of pyrite in microbial cultures has only rarely been achieved. The present work relies on chemical monitoring, electron microscopy, X-ray diffraction, and synchrotron-based spectroscopy to evaluate the formation of iron sulfides by the sulfate-reducing bacteria Desulfovibrio desulfuricans as a function of the source of iron, either provided as dissolved Fe2+ or as Fe^III-phosphate nanoparticles. Dissolved ferrous iron led to the formation of increasingly crystalline mackinawite (FeS) with time, encrusting bacterial cell walls, hence preventing further sulfate reduction upon day 5 and any evolution of iron sulfides into more stable phases, e.g., pyrite. In contrast, ferric phosphate was transformed into a mixture of large flattened crystals of well-crystallized vivianite (Fe3(PO4)2⋅8H2O) and a biofilm-like thin film of poorly crystallized mackinawite. Although being hosted in the iron sulfide biofilm, most cells were not encrusted. Excess sulfide delivered by the bacteria and oxidants (such as polysulfides) promoted the evolution of mackinawite into greigite (Fe3S4) and the nucleation of pyrite spherules. These spherules were several hundreds of nanometers wide and occurred within the extracellular polymeric substance (EPS) of the biofilm after only 1 month. Altogether, the present study demonstrates that the mineral assemblage induced by the metabolic activity of sulfate-reducing bacteria strongly depends on the source of iron, which has strong implications for the interpretation of the presence of pyrite and vivianite in natural environments.

黄铁矿或二硫化铁是地球表面上最常见的硫化物矿物，并且在地质记录中广泛分布。由于硫化物主要由现代沉积环境中的硫酸盐还原细菌（SRB）产生，因此微生物被认为可驱动硫化铁的形成，特别是黄铁矿的形成。然而，微生物在黄铁矿形成中所起的确切作用仍不清楚，迄今为止，微生物培养物中黄铁矿的沉淀很少。目前的工作依靠化学监测，电子显微镜，X射线衍射和基于同步加速器的光谱学来评估硫酸盐还原细菌形成的硫化铁的形成。脱硫弧菌 根据铁的来源（以溶解状态提供） 铁2+或作为Fe ^III-磷酸盐纳米粒子。随着时间的流逝，溶解的亚铁导致逐渐形成越来越多的结晶马基钠铁矿（FeS），包裹细菌细胞壁，从而阻止了第5天硫酸盐的进一步还原以及任何硫化铁向更稳定相（如黄铁矿）的释放。相比之下，磷酸铁会转变成结晶良好的堇青石大块扁平晶体的混合物（铁3（PO4）2⋅8H2Ø）和结晶度差的麦基钠钙石的生物膜状薄膜。尽管寄居在硫化铁生物膜中，但大多数细胞并未结壳。细菌和氧化剂传递的过量硫化物（例如多硫化物）促进了麦基钠长石向钙长石的演化（铁3小号4）和黄铁矿小球的形核。这些小球的宽度为数百纳米，仅在1个月后就出现在生物膜的细胞外聚合物质（EPS）中。总而言之，本研究表明，由减少硫酸盐的细菌的代谢活性诱导的矿物组合强烈取决于铁的来源，这对解释自然环境中黄铁矿和堇青石的存在具有重要的意义。