Heterotrophic microbes are central to organic matter degradation and transformation in marine sediments. Currently, most investigations of benthic microbiomes do not differentiate between processes in the porewater and on the grains and, hence, only show a generalized picture of the community. This limits our understanding of the structure and functions of sediment microbiomes. To address this problem, we fractionated sandy surface sediment microbial communities from a coastal site in Isfjorden, Svalbard, into cells associated with the porewater, loosely attached to grains, and firmly attached to grains; we found dissimilar bacterial communities and metabolic activities in these fractions. Most (84%–89%) of the cells were firmly attached, and this fraction comprised more anaerobes, such as sulfate reducers, than the other fractions. The porewater and loosely attached fractions (3% and 8%–13% of cells, respectively) had more aerobic heterotrophs. These two fractions generally showed a higher frequency of dividing cells, polysaccharide (laminarin) hydrolysis rates, and per-cell O2 consumption than the firmly attached cells. Thus, the different fractions occupy distinct niches within surface sediments: the firmly attached fraction is potentially made of cells colonizing areas on the grain that are protected from abrasion, but might be more diffusion-limited for organic matter and electron acceptors. In contrast, the porewater and loosely attached fractions are less resource-limited and have faster growth. Their cell numbers are kept low possibly through abrasion and exposure to grazers. Differences in community composition and activity of these cell fractions point to their distinct roles and contributions to carbon cycling within surface sediments.

中文翻译：

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细菌群落中的生态位分离和孔隙水中的活动，渗透性表面沉积物中松散附着和牢固附着的部分


异养微生物是海洋沉积物中有机物降解和转化的核心。目前，大多数对底栖微生物组的研究并没有区分孔隙水和颗粒上的过程，因此仅显示了群落的一般情况。这限制了我们对沉积物微生物组结构和功能的理解。为了解决这个问题，我们将来自斯瓦尔巴群岛伊斯峡湾沿海地区的沙质表面沉积物微生物群落分成与孔隙水相关的细胞、松散地附着在谷物上的细胞和牢固地附着在谷物上的细胞；我们在这些部分中发现了不同的细菌群落和代谢活动。大多数（84％–89％）的细胞牢固地附着，并且该部分比其他部分包含更多的厌氧菌，例如硫酸盐还原剂。孔隙水和松散附着的部分（分别占细胞的 3% 和 8%–13%）有更多的需氧异养生物。与牢固附着的细胞相比，这两个部分通常表现出更高的分裂细胞频率、多糖（昆布多糖）水解率和每个细胞的 O2 消耗量。因此，不同的部分在表面沉积物中占据不同的位置：牢固附着的部分可能由细胞在谷物上的定植区域组成，这些区域受到保护而免受磨损，但对于有机物和电子受体来说可能更受扩散限制。相比之下，孔隙水和松散附着部分的资源限制较少，并且增长较快。它们的细胞数量可能由于磨损和暴露于食草动物而保持在较低水平。这些细胞组分的群落组成和活性的差异表明它们对表面沉积物内碳循环的不同作用和贡献。