Aerobic denitrification by Paracoccus sp. YF1 in the presence of Cu(II)

This study of Cu(II)'s impact on aerobic denitrification of Paracoccus sp. YF1 revealed that the denitrification rate decreased markedly from 99.8%, 98.0%, 68.7% to 16.3% when the concentrations of Cu(II) rose from 0, 0.01 mM, 0.05 mM to 0.1 mM, respectively. This outcome was confirmed by the successful test of OD₆₀₀, total protein and enzyme activities. As the concentration of Cu(II) increased from 0 to 0.1 mM, the total protein contents declined over a period of 48 h, and the activities of nitrate reductase (NR) and nitrite reductase (NIR) decreased remarkably during the first 24 h in a NO₃^- sufficient state. Meanwhile, the reduction of NO₃^- and NO₂^- was positively correlated with the expression level of NR and NIR. The removal rate of nitrate in the control treatment and different concentration of Cu(II) treatment fitted approximately to the zero-order model. Scanning electron microscopy (SEM) confirmed that the cell surfaces of Paracoccus sp. YF1 were disrupted when exposed to 0.1 mM Cu(II). The adsorption of Cu(II) onto the cells' surface was confirmed by Energy dispersive spectrometer (EDS), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy analysis (XPS). The insights obtained here regarding the influence of Cu(II) on aerobic denitrification will be of great significance for the treatment of heavy metals and nitrite co-existing sewage.