Molecular Detection of Candidatus Scalindua pacifica and Environmental Responses of Sediment Anammox Bacterial Community in the Bohai Sea, China

The Bohai Sea is a large semi-enclosed shallow water basin, which receives extensive river discharges of various terrestrial and anthropogenic materials such as sediments, nutrients and contaminants. How these terrigenous inputs may influence the diversity, community structure, biogeographical distribution, abundance and ecophysiology of the sediment anaerobic ammonium oxidation (anammox) bacteria was unknown. To answer this question, an investigation employing both 16S rRNA and hzo gene biomarkers was carried out. Ca. Scalindua bacteria were predominant in the surface sediments of the Bohai Sea, while non-Scalindua anammox bacteria were also detected in the Yellow River estuary and inner part of Liaodong Bay that received strong riverine and anthropogenic impacts. A novel 16S rRNA gene sequence clade was identified, putatively representing an anammox bacterial new candidate species tentatively named “Ca. Scalindua pacifica”. Several groups of environmental factors, usually with distinct physicochemical or biogeochemical natures, including general marine and estuarine physicochemical properties, availability of anammox substrates (inorganic N compounds), alternative reductants and oxidants, environmental variations caused by river discharges and associated contaminants such as heavy metals, were identified to likely play important roles in influencing the ecology and biogeochemical functioning of the sediment anammox bacteria. In addition to inorganic N compounds that might play a key role in shaping the anammox microbiota, organic carbon, organic nitrogen, sulfate, sulfide and metals all showed the potentials to participate in the anammox process, releasing the strict dependence of the anammox bacteria upon the direct availability of inorganic N nutrients that might be limiting in certain areas of the Bohai Sea. The importance of inorganic N nutrients and certain other environmental factors to the sediment anammox microbiota suggests that these bacteria were active for the in situ N transforming process and maintained a versatile life style well adapted to the varying environmental conditions of the studied coastal ocean.

渤海是大型半封闭浅海盆地，接纳大量河流输入的各类陆源及人为来源物质，包括沉积物、营养盐与污染物。目前尚不明确这些陆源输入物会如何影响沉积物中厌氧氨氧化（anaerobic ammonium oxidation, anammox）细菌的多样性、群落结构、生物地理分布、丰度及生理生态特性。为解答该问题，本研究同时采用16S rRNA与hzo基因生物标志物开展了调查分析。候选梯状菌属（Candidatus Scalindua）细菌是渤海表层沉积物中的优势类群，而在受强烈河流与人为活动影响的黄河口及辽东湾内湾区域，也检测到了非梯状菌属的厌氧氨氧化细菌。本研究鉴定出一个全新的16S rRNA基因序列进化枝，推测其代表一个厌氧氨氧化细菌新候选物种，暂命名为“候选太平洋梯状菌（Candidatus Scalindua pacifica）”。研究识别出多组具有独特物理化学或生物地球化学属性的环境因子，涵盖常规海洋与河口物理化学特征、厌氧氨氧化底物（无机氮化合物）的可利用性、替代还原剂与氧化剂、河流输入及其伴生污染物（如重金属）引发的环境变化，上述因子可能对沉积物厌氧氨氧化细菌的生态及生物地球化学功能具有重要调控作用。除了可能在塑造厌氧氨氧化微生物群落结构中发挥关键作用的无机氮化合物外，有机碳、有机氮、硫酸盐、硫化物及重金属均显示出参与厌氧氨氧化过程的潜力，打破了厌氧氨氧化细菌对无机氮营养盐直接可利用性的严格依赖——而在渤海部分区域，无机氮营养盐可能为限制性因子。无机氮营养盐及其他部分环境因子对沉积物厌氧氨氧化微生物群落的重要性表明，这些细菌在原位氮转化过程中具有活性，并演化出灵活的生活策略以适应所研究近海区域多变的环境条件。