Microbe-mineral interactions can produce unique composite materials, which can preserve biosignatures. Geological evidence suggests that iron sulfide (Fe-S) minerals are abundant in the subsurface of Mars. On Earth, the formation of Fe-S minerals is driven by sulfate-reducing microorganisms (SRM) that produce reactive sulfide. Moreover, SRM metabolites, as well as intact cells, can influence the morphology, particle size, aggregation, and composition of biogenic Fe-S minerals. In this work, we evaluated how simple and complex organic molecules—hexoses and amino acid/peptide mixtures, respectively—influence the formation of Fe-S minerals (simulated prebiotic conditions), and whether the observed patterns mimic the biological influence of SRM. To this end, organo-mineral aggregates were characterized with X-ray diffraction, scanning electron microscopy, and scanning transmission X-ray microscopy coupled to near-edge X-ray absorption fine structure spectroscopy. Overall, Fe-S minerals were found to have a strong affinity for proteinaceous organic matter. Fe-S minerals precipitated at simulated prebiotic conditions yielded organic carbon distributions that were more homogeneous than treatments with whole SRM cells. In prebiotic experiments, spectroscopy detected potential organic transformations during Fe-S mineral formation, including conversion of hexoses to sugar acids and polymerization of amino acids/peptides into larger peptides/proteins. In addition, prebiotic mineral-carbon assemblages produced nanometer-scaled filamentous aggregated morphologies. On the contrary, in biotic treatments with cells, organic carbon in minerals displayed a more heterogeneous distribution. Notably, “hot spots” of organic carbon and oxygen-containing functional groups, with the size, shape, and composition of microbial cells, were preserved in mineral aggregates. We propose a list of characteristics that could be used to help distinguish biogenic from prebiotic/abiotic Fe-S minerals and help refine the search of extant or extinct microbial life in the martian subsurface.

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硫化铁矿物和有机碳之间的相互作用：对生物特征保存和检测的影响

微生物-矿物质相互作用可以产生独特的复合材料，可以保留生物特征。地质证据表明，硫化铁 (Fe-S) 矿物在火星的地下丰富。在地球上，Fe-S 矿物的形成是由产生活性硫化物的硫酸盐还原微生物 (SRM) 驱动的。此外，SRM 代谢物以及完整细胞会影响生物 Fe-S 矿物的形态、粒径、聚集和组成。在这项工作中，我们评估了简单和复杂的有机分子（分别是己糖和氨基酸/肽混合物）如何影响 Fe-S 矿物质的形成（模拟益生元条件），以及观察到的模式是否模拟了 SRM 的生物影响。为此，有机矿物聚集体用 X 射线衍射表征，扫描电子显微镜和扫描透射 X 射线显微镜与近边缘 X 射线吸收精细结构光谱耦合。总体而言，发现 Fe-S 矿物对蛋白质有机物具有很强的亲和力。在模拟的益生元条件下沉淀的 Fe-S 矿物质产生的有机碳分布比用整个 SRM 细胞处理更均匀。在益生元实验中，光谱学检测到 Fe-S 矿物形成过程中潜在的有机转化，包括己糖转化为糖酸以及氨基酸/肽聚合成更大的肽/蛋白质。此外，益生元矿物碳组合产生了纳米级的丝状聚集形态。相反，在用细胞进行生物治疗时，矿物中的有机碳呈现出更不均匀的分布。值得注意的是，有机碳和含氧官能团的“热点”，以及微生物细胞的大小、形状和组成，都保存在矿物聚集体中。我们提出了一系列特征，可用于帮助区分生物与益生元/非生物 Fe-S 矿物质，并有助于完善对火星地下现存或灭绝微生物生命的搜索。