Geochemical and quinone biomarker concentrations in the Black Sea water column and sediments@en

The stratified water column of the Black Sea serves as a model ecosystem for studying the interactions of microorganisms with major biogeochemical cycles. Here, we provide detailed analysis of isoprenoid quinones to study microbial redox processes in the ocean. In a continuum from the photic zone through the chemocline into deep anoxic sediments of the southern Black Sea, diagnostic quinones and inorganic geochemical parameters indicate niche segregation between redox processes and corresponding shifts in microbial community composition. Quinones specific for oxygenic photosynthesis and aerobic respiration dominate oxic waters, while quinones associated with thaumarchaeal ammonia oxidation and bacterial methanotrophy, respectively, dominate a narrow interval in suboxic waters. Quinone distributions indicate highest metabolic diversity within the anoxic zone, with anoxygenic photosynthesis being a major process in its photic layer. In the dark anoxic layer, quinone profiles indicate the occurrence of bacterial sulfur and nitrogen cycling, archaeal methanogenesis, and archaeal methanotrophy. Multiple novel ubiquinone isomers, possibly originating from unidentified intra-aerobic anaerobes, occur in this zone. The respiration modes found in the anoxic zone continue into shallow subsurface sediments, but quinone abundances rapidly decrease within the upper 50 cm below the sea floor, reflecting the transition to lower energy availability. In the deep subseafloor sediments, quinone distributions and geochemical profiles indicate archaeal methanogenesis/methanotrophy and potentially bacterial fermentative metabolisms. We observed that sedimentary quinone distributions track lithology, which supports prior hypotheses that deep biosphere community composition and metabolisms are determined by environmental conditions during sediment deposition.黑海的分层水柱是研究微生物与主要生物地球化学循环相互作用的模式生态系统。在此，我们通过对类异戊二烯醌（isoprenoid quinones）的详细分析，探究海洋中的微生物氧化还原过程。研究覆盖了从透光层（photic zone）经化学跃层（chemocline）至黑海南部深层缺氧沉积物的连续剖面，标志性醌类与无机地球化学参数表明，氧化还原过程间存在生态位分化，且微生物群落组成随之发生相应转变。针对产氧光合作用与有氧呼吸的特异性醌类在含氧水体中占主导地位；而分别对应奇古菌氨氧化（thaumarchaeal ammonia oxidation）与细菌甲烷氧化（bacterial methanotrophy）的醌类，则在次含氧水体的狭窄区间内占据优势。醌类分布显示缺氧层内的代谢多样性最高，其中不产氧光合作用（anoxygenic photosynthesis）是该层透光亚层的主要过程。在黑暗缺氧层中，醌类谱图表明存在细菌硫、氮循环，古菌产甲烷作用（archaeal methanogenesis）以及古菌甲烷氧化（archaeal methanotrophy）。该区域还存在多种新型泛醌异构体（novel ubiquinone isomers），其来源可能为尚未被发现的胞内有氧厌氧菌（intra-aerobic anaerobes）。缺氧层中发现的呼吸模式同样存在于浅层地下沉积物中，但在海底以下50厘米的深度范围内，醌类丰度迅速下降，这反映了能量可利用性降低的环境转变。在海底深部沉积物中，醌类分布与地球化学特征表明存在古菌产甲烷/甲烷氧化作用，以及潜在的细菌发酵代谢。我们观察到沉积醌类分布与岩性（lithology）相匹配，这支持了此前的假说：深部生物圈（deep biosphere）的群落组成与代谢模式由沉积物沉积时的环境条件所决定。