Manganese oxidation-reduction coupling denitrification performance of strain Pseudomonas sp. XFQ: Dual-function comparison and potential mechanisms.

In response to the nitrate (NO-N) and manganese (Mn) contamination in aquatic systems polluted by industrial and agricultural activities, this study isolated a strain Pseudomonas sp. XFQ that can simultaneously achieve Mn redox coupled denitrification. In the Mn(Ⅱ) oxidation-coupled denitrification system (carbon to nitrogen ratio = 2.0, Mn(Ⅱ) = 10 mg L, and pH = 7.0), the denitrification process by strain XFQ reached 98 % NO-N elimination within 12 h. Meanwhile, the Mn(Ⅳ)-driven denitrification system achieved 99 % NO-N removal within 16 h at a MnO dosage of 500 mg L. A comparison between Mn(Ⅱ) oxidation and Mn(Ⅳ) reduction driven denitrification systems showed that the nitrate reductase and nitrite reductase levels, electron transfer capacity, the intensity of Mn(III), and the membrane-intact cell counts are all lower in the Mn reduction-driven system. The introduction of gallic acid (GA) enhanced the electron transfer chain activity by regulating the complex stability of Mn(Ⅲ), redox-mediating ability, and the denitrification enzyme activity in the Mn(Ⅳ) reduction-coupled denitrification system, while promoting the co-metabolic degradation efficiency of NO-N and diclofenac. This significantly enhances Mn transformation efficiency in the Mn redox-coupled denitrification system, thereby improving Mn cycling, denitrification effectiveness, and DCF removal.