Geomicrobiology, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
Appl Environ Microbiol. 2012 Oct;78(20):7185-96. doi: 10.1128/AEM.01440-12. Epub 2012 Aug 3.
Fuschna Spring in the Swiss Alps (Engadin region) is a bicarbonate iron(II)-rich, pH-neutral mineral water spring that is dominated visually by dark green microbial mats at the side of the flow channel and orange iron(III) (oxyhydr)oxides in the flow channel. Gradients of O(2), dissolved iron(II), and bicarbonate establish in the water. Our goals were to identify the dominating biogeochemical processes and to determine to which extent changing geochemical conditions along the flow path and seasonal changes influence mineral identity, crystallinity, and microbial diversity. Geochemical analysis showed microoxic water at the spring outlet which became fully oxygenated within 2.3 m downstream. X-ray diffraction and Mössbauer spectroscopy revealed calcite (CaCO(3)) and ferrihydrite [Fe(OH)(3)] to be the dominant minerals which increased in crystallinity with increasing distance from the spring outlet. Denaturing gradient gel electrophoresis banding pattern cluster analysis revealed that the microbial community composition shifted mainly with seasons and to a lesser extent along the flow path. 16S rRNA gene sequence analysis showed that microbial communities differ between the flow channel and the flanking microbial mat. Microbial community analysis in combination with most-probable-number analyses and quantitative PCR (qPCR) showed that the mat was dominated by cyanobacteria and the channel was dominated by microaerophilic Fe(II) oxidizers (1.97 × 10(7) ± 4.36 × 10(6) 16S rRNA gene copies g(-1) using Gallionella-specific qPCR primers), while high numbers of Fe(III) reducers (10(9) cells/g) were identified in both the mat and the flow channel. Phototrophic and nitrate-reducing Fe(II) oxidizers were present as well, although in lower numbers (10(3) to 10(4) cells/g). In summary, our data suggest that mainly seasonal changes caused microbial community shifts, while geochemical gradients along the flow path influenced mineral crystallinity.
瑞士阿尔卑斯山的富歇纳泉（恩加丁地区）是一处重碳酸盐铁(II)丰富、pH 值中性的矿泉，泉水从渠道一侧的深绿色微生物垫到渠道中的橙色铁(III)（氧）氢氧化物，视觉上呈现出明显的分带。在水中建立了氧气(O2)、溶解的铁(II)和重碳酸盐的浓度梯度。我们的目标是确定主要的生物地球化学过程，并确定沿水流路径和季节变化的变化地球化学条件对矿物成分、结晶度和微生物多样性的影响程度。地球化学分析表明，泉水出口处的水呈微氧状态，在下游 2.3 米处完全充氧。X 射线衍射和穆斯堡尔光谱表明，方解石（CaCO3）和水铁矿[Fe(OH)(3)]是主要矿物，随着距离泉水出口的增加，结晶度增加。变性梯度凝胶电泳带型聚类分析表明，微生物群落组成主要随季节变化，其次是沿水流路径变化。16S rRNA 基因序列分析表明，微生物群落在流道和侧翼微生物垫之间存在差异。微生物群落分析结合最可能数分析和定量 PCR(qPCR)表明，垫主要由蓝藻主导，而通道主要由微需氧 Fe(II)氧化菌主导（使用 Gallionella 特异性 qPCR 引物，1.97×10(7)±4.36×10(6)16S rRNA 基因拷贝/g），而在垫和流道中都鉴定出大量的 Fe(III)还原菌（10(9)个细胞/g）。虽然数量较少（10(3)至 10(4)个细胞/g），但也存在光养和硝酸盐还原的 Fe(II)氧化菌。总之，我们的数据表明，主要是季节性变化导致了微生物群落的变化，而沿水流路径的地球化学梯度影响了矿物的结晶度。
