Diversity of bacterial populations in abandoned Sitarjevec mine (Slovenia) with iron oxide/hydroxide formations

Abandoned Sitarjevec mine represents specific environment (completely dark, 10 degrees C, pH<3) with various ores (lead, mercury, zinc, iron, copper) and many different minerals (anglesite, baryte, cinnabar, pyrite, cerussite, quartz, siderite). The aim of the study was characterisation of iron oxide/hydroxide speleothem with extremely fast growth of up to 5 cm/year. Morphological and chemical characterisation of iron oxide/hydroxide speleothem showed that it has layered structure with different ferrihydrite minerals (goethite, feroxyhyte, lepidocrocite). SEM-EDS confirmed that surface layers are very porous while inner parts, bulk is compact. Bacterial populations in iron oxide/hydroxide speleothem and its environment were evaluated with analysis of 16S rRNA sequencing. Results revealed great diversity of bacteria including 19-34 phyla in different samples. Proteobacteria were dominant (60-95%) in all samples, but in sample of water at iron oxide/hydroxide speleothem the highest bacterial diversity was found with 670 different genera and 100 different species. Among them typical iron oxidizing bacteria such as Gallionella capsiferriformans, Sideroxydans lithotrophicus, Sphingomonas echinoides, Candidatus Nitrotoga Nitrotoga, Leptospirillum ferrooxidans, and Ferrovum myxofaciens were identified. These iron oxidizing bacteria were not found in other samples and along with structure of iron oxide/hydroxide speleothem these might indicate involvement of bacteria in growth of this speleothem. But specific bacterial interactions with minerals and environmental conditions in the mine need to be further analysed and evaluated.

废弃西塔尔耶维奇矿（Abandoned Sitarjevec mine）是一类特殊极端环境：全程黑暗、温度恒定10℃、pH值小于3，赋存多种金属矿石（铅、汞、锌、铁、铜）与丰富矿物（铅矾（anglesite）、重晶石（baryte）、辰砂（cinnabar）、黄铁矿（pyrite）、白铅矿（cerussite）、石英（quartz）、菱铁矿（siderite））。本研究旨在对生长速率高达5 cm/年的铁氧化物/氢氧化物洞穴沉积体（iron oxide/hydroxide speleothem）进行表征分析。对该铁氧化物/氢氧化物洞穴沉积体的形貌与化学表征结果显示，其具有层状结构，且包含多种水铁矿族矿物（针铁矿（goethite）、六方纤铁矿（feroxyhyte）、斜方纤铁矿（lepidocrocite））。扫描电子显微镜-能谱仪联用（SEM-EDS）分析证实，其表层孔隙度极高，而内部主体结构致密紧实。通过16S核糖体RNA测序（16S rRNA sequencing）技术，对该铁氧化物/氢氧化物洞穴沉积体及其所处环境中的细菌群落进行了评估分析。分析结果揭示了样本中极高的细菌多样性：不同样本的细菌类群涵盖19至34个菌门。所有样本中均以变形菌门（Proteobacteria）为优势菌门，占比达60%~95%；而在该铁氧化物/氢氧化物洞穴沉积体周边的水样样本中，细菌多样性最高，共检出670个不同菌属与100个不同菌种。其中检出了典型的铁氧化细菌，包括磁尖杆菌（Gallionella capsiferriformans）、嗜铁栖氧菌（Sideroxydans lithotrophicus）、刺鞘氨醇单胞菌（Sphingomonas echinoides）、候选硝化螺菌属（Candidatus Nitrotoga）、氧化钩端螺菌（Leptospirillum ferrooxidans）以及黏质铁生菌（Ferrovum myxofaciens）。这类铁氧化细菌仅在该水样样本中被检出，结合该铁氧化物/氢氧化物洞穴沉积体的结构特征，提示细菌可能参与了该沉积体的形成过程。但该矿井内细菌与矿物间的特异性相互作用及环境调控机制仍有待进一步分析与验证。