Chloroflexi are widespread in subsurface environments, and recent studies indicate that they represent a major fraction of the communities in subseafloor sediment. Here, we compare the abundance, diversity, metabolic potential and gene expression of Chloroflexi from three abyssal sediment cores from the western North Atlantic Gyre (water depth >5400 m) covering up to 15 million years of sediment deposition, where Chloroflexi were found to represent major components of the community at all sites. Chloroflexi communities die off in oxic red clay over 10–15 million years, and gene expression was below detection. In contrast, Chloroflexi abundance and gene expression at the anoxic abyssal clay site increase below the seafloor and peak in 2–3 million-year-old sediment, indicating a comparably higher activity. Metatranscriptomes from the anoxic site reveal increased expression of Chloroflexi genes involved in cell wall biogenesis, protein turnover, inorganic ion transport, defense mechanisms and prophages. Phylogenetic analysis shows that these Chloroflexi are closely related to homoacetogenic subseafloor clades and actively transcribe genes involved in sugar fermentations, gluconeogenesis and Wood–Ljungdahl pathway in the subseafloor. Concomitant expression of cell division genes indicates that these putative homoacetogenic Chloroflexi are actively growing in these million-year-old anoxic abyssal sediments.

中文翻译：

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探索百万年含氧和缺氧深海粘土中海底 Chloroflexi 的丰度、代谢潜力和基因表达

Chloroflexi 在地下环境中广泛存在，最近的研究表明它们代表了海底沉积物中群落的主要部分。在这里，我们比较了来自北大西洋环流西部（水深 > 5400 m）的三个深海沉积物核心的 Chloroflexi 的丰度、多样性、代谢潜力和基因表达，这些沉积物覆盖了长达 1500 万年的沉积物沉积，其中 Chloroflexi 被发现代表所有地点社区的主要组成部分。Chloroflexi 群落在含氧红粘土中经过 10-1500 万年就会死亡，并且基因表达低于检测范围。相比之下，缺氧深海粘土地点的 Chloroflexi 丰度和基因表达在海底以下增加，并在 2-3 百万年前的沉积物中达到峰值，表明其活动相对较高。来自缺氧位点的宏转录组揭示了参与细胞壁生物发生、蛋白质周转、无机离子运输、防御机制和前噬菌体的 Chloroflexi 基因表达增加。系统发育分析表明，这些 Chloroflexi 与海底同型产乙酸分支密切相关，并积极转录参与海底糖发酵、糖异生和 Wood-Ljungdahl 途径的基因。细胞分裂基因的同时表达表明这些假定的同型产乙酸 Chloroflexi 在这些百万年的缺氧深海沉积物中活跃生长。