Abstract Many microorganisms including free-living and symbiotic fungi weather minerals through the formation of biofilms on their surface. Weathering thus proceeds not only according to the mineral's chemistry and the environmental conditions but also according to the local biofilm chemistry. These processes can be dissected in experiments with defined environmental settings and by employing genetic tools to modify traits of the fungal biofilm. Biofilms of the rock-inhabiting fungus Knufia petricola strain A95 (wild-type, WT) and its melanin-deficient mutant (ΔKppks) were grown on polished olivine sections in subaerial (air-exposed) and subaquatic (submerged) conditions. After seven months of interaction at pH 6 and 25 °C, the fungus-mineral interface and abiotic olivine surface were compared using high resolution transmission electron microscopy (HRTEM). The abiotic, subaquatic olivine section showed a 25 nm thick, continuous amorphous layer, enriched in Fe and depleted in Si compared to the underlying crystalline olivine. This amorphous layer formed either through a coupled interfacial dissolution reprecipitation mechanism or through the adsorption of silicic acid on precipitated ferric hydroxides. Its thickness was likely enhanced by mechanical stresses of polishing. Directly underneath a fungal biofilm (WT and mutant alike), the surface remained mostly crystalline and was strongly etched and weathered, indicating enhanced olivine dissolution. The correlation between enhanced olivine dissolution and the absence of a continuous amorphous layer is a strong indication of the dissolution-inhibiting qualities of the latter. We propose that the fungal biofilm sequesters significant amounts of Fe, preventing formation of the amorphous layer and driving olivine dissolution onwards. The seemingly similar olivine surface underneath both WT and mutant biofilms illustrates the comparably insignificant role of specific biofilm traits in the weathering of olivine once biofilm attachment is imposed. Under subaerial conditions, the absence of water on the abiotic surface prohibited olivine dissolution. This was overcome by the water retention capacities of both the WT and mutant biofilm: the olivine surface underneath subaerial fungal biofilms was as weathered as the corresponding subaquatic olivine surface. Under the studied environmental settings, the effect of fungal biofilms on olivine weathering seems to be universal, independent of the production of melanin, the composition of extracellular polymeric substances (EPS) or air-exposure.

中文翻译：

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真菌生物膜诱导橄榄石风化的高分辨率成像

摘要 许多微生物，包括自由生活和共生真菌，通过在其表面形成生物膜来风化矿物质。因此，风化作用不仅取决于矿物的化学性质和环境条件，还取决于当地的生物膜化学性质。这些过程可以在具有定义环境设置的实验中进行剖析，并通过使用遗传工具来修改真菌生物膜的特征。岩石栖息真菌 Knufia petricola 菌株 A95（野生型，WT）及其黑色素缺乏突变体（ΔKppks）的生物膜在地面（空气暴露）和水下（淹没）条件下在抛光橄榄石切片上生长。在 pH 6 和 25 °C 下相互作用七个月后，使用高分辨率透射电子显微镜 (HRTEM) 比较了真菌-矿物界面和非生物橄榄石表面。与下面的结晶橄榄石相比，非生物、水下橄榄石剖面显示出 25 nm 厚的连续无定形层，富含 Fe 并缺乏 Si。该无定形层通过耦合的界面溶解再沉淀机制或通过硅酸吸附在沉淀的氢氧化铁上形成。它的厚度可能因抛光的机械应力而增加。在真菌生物膜（WT 和突变体等）的正下方，表面大部分保持结晶，并被强烈蚀刻和风化，表明橄榄石溶解增强。增强的橄榄石溶解与不存在连续无定形层之间的相关性强烈表明后者具有抑制溶解的特性。我们建议真菌生物膜隔离大量的铁，防止形成无定形层并推动橄榄石溶解。WT 和突变生物膜下方看似相似的橄榄石表面表明，一旦施加生物膜附着，特定生物膜特征在橄榄石风化中的作用相对微不足道。在地下条件下，非生物表面没有水会阻止橄榄石溶解。这被 WT 和突变生物膜的保水能力所克服：水下真菌生物膜下方的橄榄石表面与相应的水下橄榄石表面一样风化。在研究的环境设置下，真菌生物膜对橄榄石风化的影响似乎是普遍的，与黑色素的产生、细胞外聚合物 (EPS) 的组成或空气暴露无关。