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 NH4+-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. Water pH, oxidation-reduction potential (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.