Cooperative denitrification by exogenous aerobic denitrifiers and indigenous sediment microbiota in nitrate-accumulating waterbodies

Artificial aeration is widely used for self-purification and ecological remediation of nitrogen-polluted waterbodies; however, the oxygen-rich environment will limit traditional denitrification, resulting in frequent nitrate accumulation. In this study, an aerobic denitrifying bacterium was isolated, characterized, and applied to the remediation of nitrate-accumulating waterbodies. This study aimed to investigate the cooperative pattern of exogenous aerobic denitrifiers and indigenous sediment microbiota. The isolated aerobic denitrifying strain contained napA, nirK, nirS, norB and nosZ genes and was identified as Pseudomonas sp. N2. The exogenous strain Pseudomonas sp. N2 enriched Pseudomonas spp. and made it the dominant genus of the community. Furthermore, there was a 21.48 % increase in the cumulative abundance of exogenous and indigenous denitrifiers. Consequently, after 30 days, the nitrate content of the overlying water and sediment was reduced by 2.75 mg/L and 30.98 mg/kg, respectively. Metagenomic analysis showed that exogenous and indigenous denitrifiers synergistically reduced nitrate via metabolic handoffs. Correspondingly, there was an upregulation in the levels of denitrification metabolic activities, including electron transport, gene expression, and enzyme activities. This study revealed metabolic cooperations between exogenous aerobic denitrifiers and indigenous microbiota in the remediation of nitrogen-polluted waterbodies.