Corpse decomposition increases nitrogen pollution and alters the succession of nirK-type denitrifying communities in different water types

Cadaver decomposition as high-quality nutrient inputs may exert strong perturbation on the aquatic environments, such as high nitrogen or nitrate pollution. Denitrifying bacteria may reduce nitrate to nitrogen gas, thereby decreasing the nitrogen pollution and improving self-purification ability of aquatic ecosystem. However, how nirK denitrifying communities in water respond to cadaver decomposition remains unknown. Thus, we employed high-throughput sequencing and chemical analysis to investigate the succession of nirK-type denitrifying communities in tap water and Yellow river water (experimental groups) as well as their corresponding control groups during two important stages of fish corpse decomposition called advanced floating decay and sunken remains. Our data showed that the concentration of NH3-N in the experimental groups increased approximately 3-4 times compared with the control groups. Proteobacteria was the predominant phylum for nirK denitrifying communities. Several potential pathogenic genera, such as Brucella and Achromobacter, were enriched in the corpse groups. Notably, nirK-type community structures were significantly impacted by cadaver decomposition. Community structures in the corpse groups become more similar with succession, indicating community convergence at the final stage. Aquatic pH, ORP and treatment were three important factors affecting the community structures. However, water type was not a main driving factor determining carcass-associated nirK-type bacterial communities. Four phylogenetic clusters were detected in the denitrifying communities, but showed significantly different distribution between the corpse and control groups. These results provide an in-depth understanding for nirK denitrifying functional bacteria and potential pathogenic bacteria during carrion decomposition process, which offer valuable reference to environmental evaluation and management.

尸体分解作为优质营养输入源，可对水生环境产生强烈扰动，例如引发高浓度氮或硝酸盐污染。反硝化细菌可将硝酸盐还原为氮气，从而缓解氮污染、提升水生生态系统的自净能力。然而，水体中nirK型反硝化细菌群落（nirK denitrifying communities）如何响应尸体分解过程，目前仍不明晰。为此，本研究采用高通量测序与化学分析方法，探究了鱼类尸体分解两个关键阶段——高级漂浮分解期与沉没残体期——中，自来水和黄河水样（实验组）及其相应对照组内nirK型反硝化细菌群落的演替规律。研究数据显示，实验组的氨氮（NH3-N）浓度较对照组提升约3~4倍。变形菌门（Proteobacteria）是nirK型反硝化细菌群落的优势菌门。布鲁氏菌属（Brucella）、无色杆菌属（Achromobacter）等若干潜在致病菌属在尸体实验组中显著富集。值得注意的是，nirK型群落结构受尸体分解过程的显著影响；随着演替推进，尸体组的群落结构愈发相似，表明最终阶段出现群落趋同现象。水体pH值、氧化还原电位（ORP）与处理方式是影响群落结构的三大核心因素，而水体类型并非决定与尸体相关的nirK型细菌群落的主要驱动因子。本研究在反硝化细菌群落中检测到4个系统发育簇，但其在尸体组与对照组间的分布存在显著差异。上述结果深入解析了尸体分解过程中的nirK型反硝化功能菌与潜在致病菌，可为环境评价与管理提供有价值的参考依据。