Filterable microorganisms participate in dissolved organic carbon (DOC) cycling in freshwater systems, however their exact functional role remains unknown. We determined the taxonomic identity and community dynamics of prokaryotic microbiomes in the 0.22 µm-filtered fraction and unfiltered freshwater from the Conwy River (North Wales, UK) in microcosms and, using targeted metabolomics and ¹⁴C-labelling, examined their role in the utilization of amino acids, organic acids and sugars spiked at environmentally-relevant (nanomolar) concentrations. To identify changes in community structure, we used 16S rRNA amplicon and shotgun sequencing. Unlike the unfiltered water samples where the consumption of DOC was rapid, the filtered fraction showed a 3-day lag phase before the consumption started. Analysis of functional categories of clusters of orthologous groups of proteins (COGs) showed that COGs associated with energy production increased in number in both fractions with substrate addition. The filtered fraction utilized low-molecular-weight (LMW) DOC at much slower rates than the whole community. Addition of nanomolar concentrations of LMW DOC did not measurably influence the composition of the microbial community nor the rate of consumption across all substrate types in either fraction. We conclude that due to their low activity, filterable microorganisms play a minor role in LMW DOC processing within a short residence time of lotic freshwater systems.

中文翻译：

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通过大量微生物组的可过滤部分利用低分子量有机化合物


可过滤微生物参与淡水系统中的溶解有机碳（DOC）循环，但其确切的功能作用仍不清楚。我们确定了微观世界中 0.22 µm 过滤级分和康威河（英国北威尔士）未过滤淡水中原核微生物组的分类学特性和群落动态，并使用靶向代谢组学和¹⁴ C 标记，检查了它们在利用中的作用氨基酸、有机酸和糖的浓度与环境相关（纳摩尔）。为了识别群落结构的变化，我们使用了 16S rRNA 扩增子和鸟枪法测序。与 DOC 快速消耗的未过滤水样不同，过滤后的水样在消耗开始前显示出 3 天的滞后期。对蛋白质直系同源基团 (COG) 簇功能类别的分析表明，随着底物的添加，两个组分中与能量产生相关的 COG 数量均有所增加。过滤后的部分利用低分子量 (LMW) DOC 的速度比整个群落慢得多。添加纳摩尔浓度的 LMW DOC 并没有显着影响微生物群落的组成，也没有显着影响任一部分中所有底物类型的消耗率。我们得出的结论是，由于可过滤微生物的活性较低，因此在流动淡水系统的短停留时间内的 LMW DOC 处理中发挥着次要作用。