Lost City (mid-Atlantic ridge) is a unique oceanic hydrothermal field where carbonate-brucite chimneys are colonized by a single phylotype of archaeal Methanosarcinales, as well as sulfur- and methane-metabolizing bacteria. So far, only one submarine analog of Lost City has been characterized, the Prony Bay hydrothermal field (New Caledonia), which nonetheless shows more microbiological similarities with ecosystems associated with continental ophiolites. This study presents the microbial ecology of the ‘Lost City’-type Old City hydrothermal field, recently discovered along the southwest Indian ridge. Five carbonate-brucite chimneys were sampled and subjected to mineralogical and geochemical analyses, microimaging, as well as 16S rRNA-encoding gene and metagenomic sequencing. Dominant taxa and metabolisms vary between chimneys, in conjunction with the predicted redox state, while potential formate- and CO-metabolizing microorganisms as well as sulfur-metabolizing bacteria are always abundant. We hypothesize that the variable environmental conditions resulting from the slow and diffuse hydrothermal fluid discharge that currently characterizes Old City could lead to different microbial populations between chimneys that utilize CO and formate differently as carbon or electron sources. Old City discovery and this first description of its microbial ecology opens up attractive perspectives for understanding environmental factors shaping communities and metabolisms in oceanic serpentinite-hosted ecosystems.

失落的城市（大西洋中脊）是一个独特的海洋热液场，碳酸盐水镁石烟囱被单一的古细菌 Methanosarcinales 以及硫和甲烷代谢细菌定殖。到目前为止，只有一个类似“失落之城”的海底类似物被描述，即普罗尼湾热液场（新喀里多尼亚），但它与大陆蛇绿岩相关的生态系统显示出更多的微生物相似性。这项研究展示了最近在印度西南部山脊发现的“失落之城”型旧城热液场的微生物生态学。对五个碳酸盐水镁石烟囱进行了取样，并对其进行了矿物学和地球化学分析、显微成像以及 16S rRNA 编码基因和宏基因组测序。烟囱之间的主要分类群和新陈代谢不同，结合预测的氧化还原状态，潜在的甲酸盐和 CO 代谢微生物以及硫代谢细菌总是很丰富。我们假设，由当前老城特征的缓慢和扩散的热液排放导致的可变环境条件可能导致烟囱之间不同的微生物种群，这些烟囱利用二氧化碳和甲酸盐作为碳或电子源的方式不同。老城的发现和对其微生物生态学的首次描述为了解影响海洋蛇纹岩生态系统中群落和新陈代谢的环境因素开辟了有吸引力的视角。我们假设，由当前老城特征的缓慢和扩散的热液排放导致的可变环境条件可能导致烟囱之间不同的微生物种群，这些烟囱利用二氧化碳和甲酸盐作为碳或电子源的方式不同。老城的发现和对其微生物生态学的首次描述为了解影响海洋蛇纹岩生态系统中群落和新陈代谢的环境因素开辟了有吸引力的视角。我们假设，由当前老城特征的缓慢和扩散的热液排放导致的可变环境条件可能导致烟囱之间不同的微生物种群，这些烟囱利用二氧化碳和甲酸盐作为碳或电子源的方式不同。老城的发现和对其微生物生态学的首次描述为了解影响海洋蛇纹岩生态系统中群落和新陈代谢的环境因素开辟了有吸引力的视角。