Fatty acids and intact polar lipids of laminated microbial sediments from St. Peter Ording, German Wadden Sea

Hidden for the untrained eye through a thin layer of sand, laminated microbial sediments occur in supratidal beaches along the North Sea coast. The inhabiting microbial communities organize themselves in response to vertical gradients of light, oxygen or sulfur compounds. We performed a fine-scale investigation on the vertical zonation of the microbial communities using a lipid biomarker approach, and assessed the biogeochemical processes using a combination of microsensor measurements and a 13C-labeling experiment. Lipid biomarker fingerprinting showed the overarching importance of cyanobacteria and diatoms in these systems, and heterocyst glycolipids revealed the presence of diazotrophic cyanobacteria even in 9 to 20 mm depth. High abundance of ornithine lipids (OL) throughout the system may derive from sulfate reducing bacteria, while a characteristic OL profile between 5 and 8 mm may indicate presence of purple non-sulfur bacteria. The fate of 13C-labeled bicarbonate was followed by experimentally investigating the uptake into microbial lipids, revealing an overarching importance of cyanobacteria for carbon fixation. However, in deeper layers, uptake into purple sulfur bacteria was evident, and a close microbial coupling could be shown by uptake of label into lipids of sulfate reducing bacteria in the deepest layer. Microsensor measurements in sediment cores collected at a later time point revealed the same general pattern as the biomarker analysis and the labeling experiments. Oxygen and pH-microsensor profiles showed active photosynthesis in the top layer. The sulfide that diffuses from deeper down and decreases just below the layer of active oxygenic photosynthesis indicates the presence of sulfur bacteria, like anoxygenic phototrophs that use sulfide instead of water for photosynthesis.

沿北海海岸的潮上带海滩中，存在着被薄层沙土覆盖、未经训练者难以察觉的层纹状微生物沉积。其中栖息的微生物群落会根据光照、氧气或硫化合物的垂直梯度进行空间排布。本研究采用脂质生物标志物法，对微生物群落的垂直分异进行了高精度调查，并结合微传感器测量与13C标记实验，对生物地球化学过程进行了评估。脂质生物标志物指纹分析结果显示，蓝细菌与硅藻在该生态系统中占据主导地位；而异形胞糖脂则表明，即便在9至20毫米的深度，也存在固氮蓝细菌。系统中广泛存在的高丰度鸟氨酸脂质（ornithine lipids, OL）可能源自硫酸盐还原菌；而5至8毫米深度区间内特征性的OL谱图，则可能指示紫色非硫细菌的存在。通过实验追踪13C标记碳酸氢盐在微生物脂质中的摄取过程，明确了蓝细菌在碳固定中的核心作用。但在更深的沉积层中，13C标记物被紫色硫细菌摄取的现象十分显著；而最底层硫酸盐还原菌的脂质中也检测到标记物，这证明了微生物间存在紧密的协同耦合关系。后续采集的沉积岩芯微传感器测量结果，与生物标志物分析及标记实验得出的整体趋势一致。氧与pH微传感器剖面数据显示，表层沉积发生了活跃的光合作用。从深部向上扩散的硫化物在产氧光合作用活跃层下方浓度降低，这表明硫细菌的存在——例如以硫化物替代水作为光合电子供体的不产氧光合营养型细菌。