Podbielski Melanie, Knoll Pamela, Brown Georgia, Huld Sigrid, Neubeck Anna, Cartwright Julyan H E, Sainz-Díaz C Ignacio, Pimentel Carlos, McMahon Sean
Grant Institute, School of GeoSciences, University of Edinburgh, Edinburgh, Scotland.
School of Biological Sciences, University of Edinburgh, Edinburgh, Scotland.
Geobiology. 2025 May-Jun;23(3):e70021. doi: 10.1111/gbi.70021.
Microscopic tubules and filaments composed of iron minerals occur in various rock types of all ages. Although typically lacking carbonaceous matter, many are reasonably interpreted as the remains of filamentous microorganisms coated with crystalline iron oxyhydroxides. Iron-oxidizing bacteria (IOB) acquire such a coating naturally during life. However, recent debates about purported microfossils have highlighted the potential for self-organized nonbiological mineral growth (particularly in chemical gardens) to form compositionally and morphologically similar tubules. How can biogenic and abiogenic iron-mineral tubules be differentiated? Here, we use optical and electron microscopy and Mössbauer spectroscopy to compare the composition, microtexture, and morphology of ferruginous chemical gardens and iron-mineralized sheaths of bacteria in the genus Leptothrix. Despite broad morphological similarity, we find that Leptothrix exhibits a narrower range of filament diameters and lower filament tortuosity than chemical gardens. Chemical gardens produced from a ferrous salt also tend to incorporate Fe whereas Leptothrix sheaths predominantly do not. Finally, the oxyhydroxides formed in Leptothrix sheaths tend to be smoother and denser on the inward-facing side, rougher and sparser on the outward side, whereas for chemical garden tubules the reverse is true. Some of these differences show promise for the diagnosis of natural samples.
由铁矿物组成的微观小管和细丝存在于各个地质年代的各类岩石中。尽管通常不含碳质物质，但许多都被合理地解释为被结晶氢氧化铁包覆的丝状微生物的遗骸。铁氧化细菌（IOB）在生命过程中会自然形成这样的包覆层。然而，最近关于所谓微化石的争论凸显了自组织非生物矿物生长（特别是在化学花园中）形成成分和形态相似小管的可能性。如何区分生物成因和非生物成因的铁矿物小管呢？在这里，我们使用光学显微镜、电子显微镜和穆斯堡尔光谱来比较铁锈色化学花园和纤发菌属细菌的铁矿化鞘的成分、微观结构和形态。尽管在形态上有广泛的相似性，但我们发现纤发菌的细丝直径范围更窄，细丝的曲折度比化学花园更低。由亚铁盐产生的化学花园也倾向于包含铁，而纤发菌的鞘主要不含铁。最后，纤发菌鞘中形成的氢氧化铁在内侧往往更光滑、更致密，外侧更粗糙、更稀疏，而化学花园小管则相反。其中一些差异有望用于天然样品的诊断。
