Microbial sulfate reduction is largely associated with anaerobic methane oxidation and alkane degradation in sulfate–methane transition zone (SMTZ) of deep-sea cold seeps. How the sulfur cycling is mediated by microbes near SMTZ has not been fully understood. In this study, we detected a shallow SMTZ in three of eight sediment cores sampled from two cold seep areas in the South China Sea. One hundred ten genomes representing sulfur-oxidizing bacteria (SOB) and sulfur-reducing bacteria (SRB) strains were identified from three SMTZ-bearing cores. In the layers above SMTZ, SOB were mostly constituted by Campylobacterota, Gammaproteobacteria and Alphaproteobacteria that probably depended on nitrogen oxides and/or oxygen for oxidation of sulfide and thiosulfate in near-surface sediment layers. In the layers below the SMTZ, the deltaproteobacterial SRB genomes and metatranscriptomes revealed CO₂ fixation by Wood–Ljungdahl pathway, sulfate reduction and nitrogen fixation for syntrophic or fermentative lifestyle. A total of 68% of the metagenome assembled genomes were not adjacent to known species in a phylogenomic tree, indicating a high diversity of bacteria involved in sulfur cycling. With the large number of genomes for SOB and SRB, our study uncovers the microbial populations that potentially mediate sulfur metabolism and associated carbon and nitrogen cycles, which sheds light on complex biogeochemical processes in deep-sea environments.

中文翻译：

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深海冷渗沉积物硫酸盐-甲烷转变附近硫循环的微生物生态学

微生物硫酸盐还原主要与深海冷泉硫酸盐-甲烷过渡区（SMTZ）的厌氧甲烷氧化和烷烃降解有关。SMTZ 附近的微生物如何介导硫循环尚未完全清楚。在这项研究中，我们在南海两个冷泉区采样的八个沉积岩芯中的三个中检测到了浅层 SMTZ。从三个含 SMTZ 的核心中鉴定出 110 个代表硫氧化细菌 (SOB) 和硫还原细菌 (SRB) 菌株的基因组。在 SMTZ 上方的层中，SOB 主要由弯曲杆菌门、伽玛变形杆菌门和阿尔法变形杆菌门构成，它们可能依赖氮氧化物和/或氧气来氧化近地表沉积层中的硫化物和硫代硫酸盐。在 SMTZ 以下的层中，₂通过 Wood-Ljungdahl 途径进行固定，硫酸盐还原和固氮用于同养或发酵生活方式。总共 68% 的宏基因组组装的基因组与系统发育树中的已知物种不相邻，这表明参与硫循环的细菌高度多样性。凭借大量 SOB 和 SRB 的基因组，我们的研究揭示了可能介导硫代谢和相关碳和氮循环的微生物种群，从而揭示了深海环境中复杂的生物地球化学过程。