Carcass decay deteriorates water quality and modifies the nirS denitrifying communities in different degradation stages.

Corpse degradation may release amounts of hazardous materials (e.g., cadaverine, putrescine and ammonia) into surrounding areas, which deteriorate environments and result in nitrogen contamination. Nitrate or nitrite can be reduced to nitrogen gas by denitrifying bacteria, thus alleviating nitrogen contamination and purifying aquatic environments. However, the reaction of nirS-encoding denitrifiers to carcass degradation is less studied. Therefore, water physiochemical analysis and high-throughput sequencing were applied to explore the successional pattern of nirS denitrifying communities in the Yellow River water and tap water during three stages of animal cadaver decay (submerged fresh, advanced floating decay as well as sunken remains) and relevant control group. Nitrate nitrogen (NO-N) and ammonia nitrogen (NH-N) concentration in corpse groups were highly elevated compared with control groups. The dominant phylum for nirS denitrifying communities was Proteobacteria. Abundant denitrifying genera Paracoccus, Alicycliphilus and Diaphorobacter were detected, and these genera have been reported to participate in the degradation of organic pollutants. Particularly, nirS-type community structures were remarkably influenced by corpse decay and became similar with succession. Water total dissolved solids (TDS), salinity, conductivity (CON) and phosphate were primary impacting factors driving the community structures, but the effect of water type was almost negligible. Notably, denitrifying community assembly was dominated by deterministic processes rather than stochastic processes, and the relative importance of deterministic processes among most corpse groups was higher than that in control groups, indicating that environmental filtering regulates the denitrifying communities. Our results provide new insight into environmental purification for hazardous materials produced by corpse degradation, thereby providing valuable advice to environmental administration.