Effects of arsenic and trace metals on bacterial denitrification process from estuarine sediments and associated nitrous oxide emission.

Coastal ecosystems currently face significant challenges due to nutrient enrichment and trace metal contamination. However, the effects of arsenic (As) and other trace metals (copper, lead, zinc, cadmium, mercury) on denitrification processes and nitrous oxide (N2O) emissions in estuarine sediments remain poorly understood. Here, we examined the influence of As and other trace metals on denitrification and N2O emissions in a single denitrifying strain, Marinobacter sp. MSD-1, isolated from metal-contaminated estuarine sediments based on its As(III)-oxidizing and denitrifying abilities and functional microbial composition. The results showed that As did not significantly affect the denitrification or N2O emission of MSD-1. However, Cd(II) at concentrations of 5-10 mg/L significantly induced the accumulation of N2O, while not significantly affecting the reduction of nitrate (NO3-) and nitrite (NO2-). The presence of As(III) further inhibited the N2O reduction under Cd exposure, but it had no significant effect on the N2O reduction after exposure to other trace metals. A negative correlation was observed between N2O reductase (NO2R) activity and N2O emissions, indicating that Cd(II) inhibits the reduction process of N2O mainly by suppressing the activity of NO2R. This study highlights the detrimental effects of cadmium on microbial denitrification and subsequent emissions of the greenhouse gas N2O, thereby improving our understanding of how estuarine and coastal ecosystems respond and adapt to trace metal pollution.