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Structure and function of denitrifying bacterial assemblages inlow-order Indiana streams

机译：低阶印第安纳流中反硝化细菌集合的结构和功能

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Anthropogenic activities increase rates of N input to the environment, and loss of this N is controlled by several factors, including denitrification. Streams are the initial receptors of terrestrial N, but the extent to which variability in stream denitrification rates are related to differences in microbial community structure are largely unexplored. In our study, the rate of denitrification and taxonomic and functional gene diversity and abundance were examined in 3 Indiana (USA) streams with differing amounts of watershed agriculture. Taxonomic and functional gene diversity were measured using terminal restriction length polymorphisms of the 16S ribosomal ribonucleic acid (rRNA) and nitrous oxide reductase (nosZ) genes, and abundance was examined using quantitative polymerase chain reaction (Q-PCR) and total direct cell counts. As expected, streams with highest amounts of watershed agriculture had highest NO~(3-) concentrations and highest sediment organic matter (OM) content leading to higher denitrification rates. Overall, denitrification rates were controlled primarily by sediment OM content and secondarily by nosZ abundance and nosZ terminal restriction fragment (T-RF) number. However, total bacterial numbers were not related to peaks in denitrification rate. The 2 sites with the most substantial differences in watershed agriculture, NO~(3-) concentrations, and sediment OM content also had the largest differences in both nosZ abundance and nosZ gene profiles. Overall, our results suggest that denitrification rates in agricultural streams are influenced by a combination of environmental variables (primarily benthic OM and NO~(3-) concentrations) and microbial community composition.
机译：人为活动增加了向环境中输入的氮的比率，该氮的损失受包括反硝化在内的若干因素控制。溪流是陆地N的初始受体，但在很大程度上尚未探究溪流反硝化速率的变化与微生物群落结构差异相关的程度。在我们的研究中，在3个印第安纳州（美国）溪流中使用不同的分水岭农业进行了研究，研究了反硝化率，分类学和功能基因多样性以及丰度。使用16S核糖体核糖核酸（rRNA）和一氧化二氮还原酶（nosZ）基因的末端限制性长度多态性来测量分类学和功能基因多样性，并使用定量聚合酶链反应（Q-PCR）和总直接细胞计数来检查丰度。不出所料，流域农业数量最多的溪流具有最高的NO〜（3-）浓度和最高的沉积物有机质（OM）含量，从而导致更高的反硝化率。总体而言，反硝化速率主要受沉积物OM含量控制，其次受nosZ丰度和nosZ末端限制片段（T-RF）数量控制。但是，总细菌数与反硝化率的峰值无关。流域农业，NO〜（3-）浓度和沉积物OM含量差异最大的2个位点在nosZ丰度和nosZ基因谱上的差异也最大。总体而言，我们的结果表明，农业流中的反硝化率受环境变量（主要是底栖生物OM和NO〜（3-）浓度）和微生物群落组成的组合影响。

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