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The ultramafic-hosted Logatchev hydrothermal field (LHF) is characterized by vent fluids, which are enriched in dissolved hydrogen and methane compared with fluids from basalt-hosted systems. Thick sediment layers in LHF are partly covered by characteristic white mats. In this study, these sediments were investigated in order to determine biogeochemical processes and key organisms relevant for primary production. Temperature profiling at two mat-covered sites showed a conductive heating of the sediments. Elemental sulfur was detected in the overlying mat and metal-sulfides in the upper sediment layer. Microprofiles revealed an intensive hydrogen sulfide flux from deeper sediment layers. Fluorescence in situ hybridization showed that filamentous and vibrioid, Arcobacter-related Epsilonproteobacteria dominated the overlying mats. This is in contrast to sulfidic sediments in basalt-hosted fields where mats of similar appearance are composed of large sulfur-oxidizing Gammaproteobacteria. Epsilonproteobacteria (7- 21%) and Deltaproteobacteria (20-21%) were highly abundant in the surface sediment layer. The physiology of the closest cultivated relatives, revealed by comparative 16S rRNA sequence analysis, was characterized by the capability to metabolize sulfur com- ponents. High sulfate reduction rates as well as sulfide depleted in 34S further confirmed the importance of the biogeochemical sulfur cycle. In contrast, methane was found to be of minor relevance for microbial life in mat-covered surface sediments. Our data indicate that in conductively heated surface sediments microbial sulfur cycling is the driving force for bacterial biomass production although ultramafic- hosted systems are characterized by fluids with high levels of dissolved methane and hydrogen.

以超镁铁质岩为赋存基底的洛加切夫热液田（Logatchev hydrothermal field, LHF）的喷口流体具有显著特征：与玄武岩赋存热液系统的流体相比，其喷口流体富含溶解氢与甲烷。洛加切夫热液田内的厚沉积物层部分被特征性白色菌席覆盖。本研究针对这些沉积物展开调查，旨在明确与初级生产相关的生物地球化学过程及关键微生物类群。对两处被菌席覆盖的点位开展温度剖面测量，结果显示沉积物存在传导加热现象。在覆盖于沉积物之上的菌席中检出单质硫，上层沉积物层则检测到金属硫化物。微剖面分析结果显示，沉积物深层存在强烈的硫化氢通量。荧光原位杂交（Fluorescence in situ hybridization）结果显示，丝状、弧菌形且与弓形杆菌属（Arcobacter）相关的ε-变形菌门（Epsilonproteobacteria）在上方覆盖的菌席中占据主导地位。这与玄武岩赋存热液田的硫化物沉积物形成鲜明反差：后者外观相似的菌席由大型硫氧化γ-变形菌门（Gammaproteobacteria）构成。表层沉积物层中，ε-变形菌门（7%~21%）与δ-变形菌门（Deltaproteobacteria，20%~21%）的丰度极高。通过16S rRNA序列比对分析获得的最近缘可培养菌株的生理特性显示，此类微生物具备代谢硫化合物的能力。高硫酸盐还原速率以及贫化34S的硫化物，进一步证实了生物地球化学硫循环的重要性。与之相反，甲烷在被菌席覆盖的表层沉积物的微生物生命活动中仅具有次要作用。本研究数据表明，尽管超镁铁质岩赋存热液系统的流体富含溶解氢与甲烷，但在传导加热的表层沉积物中，微生物硫循环是驱动细菌生物量生产的核心动力。