The oceanic crustal aquifer is one of the largest habitable volumes on Earth, and it harbors a reservoir of microbial life that influences global-scale biogeochemical cycles. Here, we use time series metagenomic and metatranscriptomic data from a low-temperature, ridge flank environment representative of the majority of global hydrothermal fluid circulation in the ocean to reconstruct microbial metabolic potential, transcript abundance, and community dynamics. We also present metagenome-assembled genomes from recently collected fluids that are furthest removed from drilling disturbances. Our results suggest that the microbial community in the North Pond aquifer plays an important role in the oxidation of organic carbon within the crust. This community is motile and metabolically flexible, with the ability to use both autotrophic and organotrophic pathways, as well as function under low oxygen conditions by using alternative electron acceptors such as nitrate and thiosulfate. Anaerobic processes are most abundant in subseafloor horizons deepest in the aquifer, furthest from connectivity with the deep ocean, and there was little overlap in the active microbial populations between sampling horizons. This work highlights the heterogeneity of microbial life in the subseafloor aquifer and provides new insights into biogeochemical cycling in ocean crust.

洋壳含水层是地球上最大的可居住体积之一，它蕴藏着影响全球范围生物地球化学循环的微生物生命库。在这里，我们使用代表海洋中大多数全球热液循环的低温脊侧环境的时间序列宏基因组和宏转录组数据来重建微生物代谢潜力、转录本丰度和群落动态。我们还展示了来自最近收集的远离钻井干扰的流体的宏基因组组装基因组。我们的结果表明，北池含水层中的微生物群落在地壳内有机碳的氧化中发挥着重要作用。该群落具有运动性和代谢灵活性，能够利用自养和有机营养途径，并通过使用硝酸盐和硫代硫酸盐等替代电子受体在低氧条件下发挥作用。厌氧过程在含水层最深处、距离深海连接最远的海底层位中最为丰富，并且采样层位之间的活跃微生物种群几乎没有重叠。这项工作强调了海底含水层中微生物生命的异质性，并为洋壳中的生物地球化学循环提供了新的见解。