Studying the effects of chemical contaminants on the structure and function of microbial and meiofauna communities have traditionally focused on specific effects of single contaminants on single species. This has left the complex interactions between mixtures of contaminants and its non-specific toxicity effects on the functions and structure of sediment microbial communities mostly overlooked. In order to improve our insights on such questions, we performed an experiment where Baltic Sea sediments were spiked with an ecologically relevant mixture of seven organic contaminants below specific toxicity levels and used 16S and 18S rRNA metabarcoding from RNA extracts to monitor changes in active microbial and meiofauna diversity and community structure in the spiked treatment compared to controls. In addition, we investigated the effects of exposure to this contaminant mixture on potential nitrification rates and on the expression of key-genes in the microbial nitrification and PAH degradation pathways with qPCR. There were significant differences in both eukaryotic and microbial community structures in sediments spiked with a mixture of organic contaminants. Nematoda showed a significant increase in overall relative abundance to the added contaminants (5.5 ± 1.1% higher in spiked), particularly taxa of the genus Leptolaimus (increased from 10.2 ± 5.4% in the controls to 32.5 ± 10.2% in the spiked treatment). Conversely, a significant decrease in relative abundance from 18.2 ± 5.6% in control to 7 ± 3.4% in of the genus Paraplectana was also detected. Additionally, while the abundance of active PAH degraders was significantly higher in spiked sediments than in the controls, no significant effect of our organic mixture was found on nitrification rates or the expression of AmoA (bacterial ammonia oxidizer gene). Our data indicate that mixtures of organic contaminants can have significant effects on microbenthic community structure even when its individual components are present at concentrations below its specific toxicity. In addition, we suggest that eRNA-based metabarcoding can offer important insights in microbenthic community structure and activities, and further empathizes the potential of meiofauna as bio-indicators of chemical contamination in benthic ecosystems.

中文翻译：

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有机污染物混合物显着改变底栖微生物群落结构并增加多环芳烃降解基因的表达

研究化学污染物对微生物和小型动物群落结构和功能的影响历来侧重于单一污染物对单一物种的特定影响。这使得污染物混合物之间复杂的相互作用及其对沉积物微生物群落的功能和结构的非特异性毒性影响大多被忽视。为了提高我们对这些问题的见解，我们进行了一项实验，在波罗的海沉积物中加入了低于特定毒性水平的七种有机污染物的生态相关混合物，并使用来自 RNA 提取物的 16S 和 18S rRNA 元条形码来监测活性微生物和与对照相比，加标处理中的小型动物多样性和群落结构。此外，我们使用 qPCR 研究了暴露于这种污染物混合物对潜在硝化速率以及微生物硝化和 PAH 降解途径中关键基因表达的影响。在掺有有机污染物混合物的沉积物中，真核和微生物群落结构存在显着差异。线虫对添加的污染物显示出总体相对丰度的显着增加（加标的高 5.5 ± 1.1%），尤其是钩端虫属的分类群（从对照的 10.2 ± 5.4% 增加到加标处理的 32.5 ± 10.2%）。相反，还检测到相对丰度从对照的 18.2 ± 5.6% 显着降低到 Paraplectana 属的 7 ± 3.4%。此外，虽然加标沉积物中活性 PAH 降解剂的丰度显着高于对照，但我们的有机混合物对硝化速率或 AmoA（细菌氨氧化剂基因）的表达没有显着影响。我们的数据表明，即使有机污染物的各个组分以低于其特定毒性的浓度存在，有机污染物的混合物也会对底栖微生物群落结构产生显着影响。此外，我们建议基于 eRNA 的元条形码可以提供对微型底栖动物群落结构和活动的重要见解，并进一步了解小型动物作为底栖生态系统中化学污染生物指标的潜力。未发现我们的有机混合物对硝化速率或 AmoA（细菌氨氧化剂基因）的表达有显着影响。我们的数据表明，即使有机污染物的各个组分以低于其特定毒性的浓度存在，有机污染物的混合物也会对底栖微生物群落结构产生显着影响。此外，我们建议基于 eRNA 的元条形码可以提供对微型底栖动物群落结构和活动的重要见解，并进一步了解小型动物作为底栖生态系统中化学污染生物指标的潜力。未发现我们的有机混合物对硝化速率或 AmoA（细菌氨氧化剂基因）的表达有显着影响。我们的数据表明，即使有机污染物的各个组分以低于其特定毒性的浓度存在，有机污染物的混合物也会对底栖微生物群落结构产生显着影响。此外，我们建议基于 eRNA 的元条形码可以提供对微型底栖动物群落结构和活动的重要见解，并进一步了解小型动物作为底栖生态系统中化学污染生物指标的潜力。