Jaussi Marion, Jørgensen Bo Barker, Kjeldsen Kasper U, Lomstein Bente A, Pearce Christof, Seidenkantz Marit-Solveig, Røy Hans
Department of Biology, Aarhus University, Aarhus, Denmark.
Department of Geoscience, Aarhus University, Aarhus, Denmark.
Front Microbiol. 2023 Jul 24;14:1198664. doi: 10.3389/fmicb.2023.1198664. eCollection 2023.
Microorganisms in subsurface sediments live from recalcitrant organic matter deposited thousands or millions of years ago. Their catabolic activities are low, but the deep biosphere is of global importance due to its volume. The stability of deeply buried sediments provides a natural laboratory where prokaryotic communities that live in steady state with their environments can be studied over long time scales. We tested if a balance is established between the flow of energy, the microbial community size, and the basal power requirement needed to maintain cells in sediments buried meters below the sea floor. We measured rates of carbon oxidation by sulfate reduction and counted the microbial cells throughout ten carefully selected sediment cores with ages from years to millions of years. The rates of carbon oxidation were converted to power (J s i.e., Watt) using the Gibbs free energy of the anaerobic oxidation of complex organic carbon. We separated energy dissipation by fermentation from sulfate reduction. Similarly, we separated the community into sulfate reducers and non-sulfate reducers based on the gene, so that sulfate reduction could be related to sulfate reducers. We found that the per-cell sulfate reduction rate was stable near 10 fmol C cell day right below the zone of bioturbation and did not decrease with increasing depth and sediment age. The corresponding power dissipation rate was 10 W sulfate-reducing cell. The cell-specific power dissipation of sulfate reducers in old sediments was similar to the slowest growing anaerobic cultures. The energy from mineralization of organic matter that was not dissipated by sulfate reduction was distributed evenly to all cells that did not possess the gene, i.e., cells operationally defined as fermenting. In contrast to sulfate reducers, the fermenting cells had decreasing catabolism as the sediment aged. A vast difference in power requirement between fermenters and sulfate reducers caused the microbial community in old sediments to consist of a minute fraction of sulfate reducers and a vast majority of fermenters.
地下沉积物中的微生物以数千或数百万年前沉积的难降解有机物质为食。它们的分解代谢活动很低，但由于其体积庞大，深层生物圈具有全球重要性。深埋沉积物的稳定性提供了一个天然实验室，在这里可以在长时间尺度上研究与环境处于稳态的原核生物群落。我们测试了在能量流动、微生物群落大小和维持海底以下数米深处沉积物中细胞所需的基础能量需求之间是否建立了平衡。我们通过硫酸盐还原测量了碳氧化速率，并对十个精心挑选的沉积岩芯中的微生物细胞进行了计数，这些岩芯的年龄从数年到数百万年不等。利用复杂有机碳厌氧氧化的吉布斯自由能，将碳氧化速率转换为能量（焦耳/秒，即瓦特）。我们将发酵产生的能量耗散与硫酸盐还原分开。同样，我们根据 基因将群落分为硫酸盐还原菌和非硫酸盐还原菌，以便将硫酸盐还原与硫酸盐还原菌联系起来。我们发现，在生物扰动带正下方，每个细胞的硫酸盐还原速率稳定在接近10飞摩尔碳/细胞·天，并且不会随着深度和沉积物年龄的增加而降低。相应的能量耗散速率为10瓦特/硫酸盐还原细胞。老沉积物中硫酸盐还原菌的细胞特异性能量耗散与生长最慢的厌氧培养物相似。未通过硫酸盐还原耗散的有机物质矿化产生的能量均匀地分配给所有不具有 基因的细胞，即被定义为发酵的细胞。与硫酸盐还原菌不同，随着沉积物老化，发酵细胞的分解代谢减少。发酵菌和硫酸盐还原菌在能量需求上的巨大差异导致老沉积物中的微生物群落由一小部分硫酸盐还原菌和绝大多数发酵菌组成。
