Carcass decay inhibits denitrification indirectly by regulating the microbiota and physicochemical properties in a model water system

Animal carcass decomposition is involved in nitrogen (N) cycle in the
aquatic ecosystems, e.g., denitrification, volatilization, and leaching.
The denitrification process is a crucial part of the nitrogen cycle,
helping to alleviate biological toxicity resulting from nitrate
accumulation. However, it is still unknown whether and how cadaver decay
affects the denitrifiers and their activity in river water. In this study,
six denitrifiers (encoding napA, narG, nirK, nirS, norB, and
nosZ, respectively) and denitrifying activity were investigated in a model
water system with nitrogen pollution from corpse decomposition using
high-throughput sequencing, real-time quantitative PCR, and denitrifying
enzyme activity (DEA) assay. Cadaver decay increased the quantity and
altered the composition of denitrifying microbiota. Multiple regression on
distance matrices revealed that corpse decay had a significantly greater
impact on the denitrification communities compared to temperature. To our
surprise, the DEA decreased in the contaminated water by cadavers. The
multiple regression models revealed that the abundance of denitrifying
taxa and the gene copies may jointly predict changes in DEA, with the
highest contribution coming from the norB-type Hydrogenophaga. Further,
the partial least squares path model (PLS-PM) showed that corpse decay
indirectly inhibited DEA via the denitrification community and water
physicochemical properties. Synthesis and applications. This study
provides important insights into how cadaver decomposition can reduce
denitrification activity in water systems. These findings can assist us in
scientifically managing and remediating polluted water bodies.