Previous exploration missions have revealed Mars as a potential candidate for the existence of extraterrestrial life. If life could have existed beneath the Martian subsurface, biosignatures would have been preserved in iron-rich minerals. Prior investigations of terrestrial biosignatures and metabolic processes of geological analogues would be beneficial for identifying past metabolic processes on Mars, particularly morphological and chemical signatures indicative of past life, where biological components could potentially be denatured following continued exposure to extreme conditions. The objective of the research was to find potential implications for Martian subsurface life by characterizing morphological, mineralogical and microbial signatures of hematite deposits, both hematite rock and related soil samples, collected from Highland Complex of Sri Lanka. Rock samples examined through scanning electron microscopy-energy dispersive X-ray (SEM-EDX) spectroscopy. Analysis showed globular and spherical growth layers nucleated by bacteria. EDX results showed a higher iron to oxygen ratio in nuclei colonies compared to growth layers, which indicated a compositional variation due to microbial interaction. X-ray diffraction analysis of the hematite samples revealed variations in chemical composition along the vertical soil profile, with the top surface soil layer being particularly enriched with Fe2O3, suggesting internal dissolution of hematite through weathering. Furthermore, inductively coupled plasma-mass spectrometry analyses carried out on both rock and soil samples showed a possible indication of microbially induced mineral-weathering, particularly release of trapped trace metals in the parent rock. Microbial diversity analysis using 16S rRNA gene sequencing revealed that the rock sample was dominated by Actinobacteria and Proteobacteria, specifically, members of iron-metabolizing bacterial genera, including Mycobacterium, Arthrobacter, Amycolatopsis, Nocardia and Pedomicrobium. These results suggest that morphological and biogeochemical clues derived from studying the role of bacterial activity in hematite weathering and precipitation processes can be implemented as potential comparative tools to interpret similar processes that could have occurred on early Mars.

中文翻译：

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细菌对赤铁矿形成的影响：对火星休眠生命的影响

之前的探索任务表明，火星是外星生命存在的潜在候选者。如果生命可以存在于火星地下，那么生物特征就会保存在富含铁的矿物中。先前对地质类似物的陆地生物特征和代谢过程的研究将有利于识别火星上过去的代谢过程，特别是指示过去生命的形态和化学特征，其中生物成分在持续暴露于极端条件下可能会变性。该研究的目的是通过表征赤铁矿沉积物（包括赤铁矿岩石和相关土壤样本）的形态、矿物学和微生物特征来发现对火星地下生命的潜在影响，采集自斯里兰卡高地综合体。通过扫描电子显微镜-能量色散 X 射线 (SEM-EDX) 光谱检查岩石样品。分析显示由细菌成核的球形和球形生长层。EDX 结果显示，与生长层相比，核菌落中的铁氧比更高，这表明由于微生物相互作用而导致的成分变化。赤铁矿样品的 X 射线衍射分析揭示了沿垂直土壤剖面的化学成分变化，表层土壤层特别富含铁 EDX 结果显示，与生长层相比，核菌落中的铁氧比更高，这表明由于微生物相互作用而导致的成分变化。赤铁矿样品的 X 射线衍射分析揭示了沿垂直土壤剖面的化学成分变化，表层土壤层特别富含铁 EDX 结果显示，与生长层相比，核菌落中的铁氧比更高，这表明由于微生物相互作用而导致的成分变化。赤铁矿样品的 X 射线衍射分析揭示了沿垂直土壤剖面的化学成分变化，表层土壤层特别富含铁2○3，表明赤铁矿通过风化在内部溶解。此外，对岩石和土壤样品进行的电感耦合等离子体质谱分析表明，可能表明微生物引起的矿物风化，特别是母岩中捕获的微量金属的释放。使用 16S rRNA 基因测序的微生物多样性分析表明，岩石样品主要由放线菌和变形菌门, 具体来说, 铁代谢细菌属的成员, 包括分枝杆菌,节杆菌,无枝菌属,诺卡氏菌和土壤微生物. 这些结果表明，从研究细菌活动在赤铁矿风化和降水过程中的作用获得的形态学和生物地球化学线索可以作为潜在的比较工具来解释早期火星上可能发生的类似过程。