Table_2_The Active Sulfate-Reducing Microbial Community in Littoral Sediment of Oligotrophic Lake Constance.XLSX

Active sulfate-reducing microorganisms (SRM) in freshwater sediments are under-examined, despite the well-documented cryptic sulfur cycle occurring in these low-sulfate habitats. In Lake Constance sediment, sulfate reduction rates of up to 1,800 nmol cm-3 day-1 were previously measured. To characterize its SRM community, we used a tripartite amplicon sequencing approach based on 16S rRNA genes, 16S rRNA, and dsrB transcripts (encoding the beta subunit of dissimilatory sulfite reductase). We followed the respective amplicon dynamics in four anoxic microcosm setups supplemented either with (i) chitin and sulfate, (ii) sulfate only, (iii) chitin only, or (iv) no amendment. Chitin was used as a general substrate for the whole carbon degradation chain. Sulfate turnover in sulfate-supplemented microcosms ranged from 38 to 955 nmol day-1 (g sediment f. wt.)-1 and was paralleled by a decrease of 90–100% in methanogenesis as compared to the respective methanogenic controls. In the initial sediment, relative abundances of recognized SRM lineages accounted for 3.1 and 4.4% of all bacterial 16S rRNA gene and 16S rRNA sequences, respectively. When normalized against the 1.4 × 108 total prokaryotic 16S rRNA gene copies as determined by qPCR and taking multiple rrn operons per genome into account, this resulted in approximately 105–106 SRM cells (g sediment f. wt.)-1. The three amplicon approaches jointly identified Desulfobacteraceae and Syntrophobacteraceae as the numerically dominant and transcriptionally most active SRM in the initial sediment. This was corroborated in the time course analyses of sulfate-consuming sediment microcosms irrespective of chitin amendment. Uncultured dsrAB family-level lineages constituted in sum only 1.9% of all dsrB transcripts, with uncultured lineage 5 and 6 being transcriptionally most active. Our study is the first holistic molecular approach to quantify and characterize active SRM including uncultured dsrAB lineages not only in Lake Constance but for lake sediments in general.

尽管淡水沉积物中的活性硫酸盐还原微生物（SRM）未得到充分研究，但这些低硫酸盐栖息地中发生的隐秘硫循环已被广泛记录。在康斯坦茨湖沉积物中，先前测得的硫酸盐还原速率高达1,800 nmol cm-3 日-1。为了表征其SRM群落，我们采用了基于16S rRNA基因、16S rRNA和dsrB转录本（编码异化亚硫酸盐还原酶的β亚基）的三联体扩增子测序方法。我们在四种无氧微宇宙设置中追踪了相应扩增子的动态变化，这些设置分别补充了（i）几丁质和硫酸盐，（ii）仅硫酸盐，（iii）仅几丁质，或（iv）不添加任何物质。几丁质被用作整个碳降解链的通用底物。在补充硫酸盐的微宇宙中，硫酸盐周转率范围为38至955 nmol 日-1（g沉积物 f. wt.-1），与相应的产甲烷控制相比，甲烷生成量下降了90–100%。在初始沉积物中，已识别的SRM谱系的相对丰度占所有细菌16S rRNA基因和16S rRNA序列的3.1%和4.4%。当将qPCR确定的1.4 × 10^8总原核生物16S rRNA基因拷贝数进行标准化，并考虑到每个基因组中多个rrn操纵子时，这导致大约105–106个SRM细胞（g沉积物 f. wt.-1）。三种扩增子方法共同确定了Desulfobacteraceae和Syntrophobacteraceae为初始沉积物中数量上占主导地位且转录活性最高的SRM。这一发现通过无论是否添加几丁质的硫酸盐消耗沉积物微宇宙的时间进程分析得到了证实。未培养的dsrAB家族水平谱系总共只占所有dsrB转录本的1.9%，其中未培养谱系5和6在转录上最为活跃。本研究是首次采用整体分子方法对活性SRM进行定量和表征，包括未培养的dsrAB谱系，不仅针对康斯坦茨湖，而且针对湖泊沉积物总体而言。