Effects of heavy metals on aerobic denitrification by strain Pseudomonas stutzeri PCN-1

Abstract

Effects of heavy metals on aerobic denitrification have been poorly understood compared with their impacts on anaerobic denitrification. This paper presented effects of four heavy metals (Cd(II), Cu(II), Ni(II), and Zn(II)) on aerobic denitrification by a novel aerobic denitrifying strain Pseudomonas stutzeri PCN-1. Results indicated that aerobic denitrifying activity decreased with increasing heavy metal concentrations due to their corresponding inhibition on the denitrifying gene expression characterized by a time lapse between the expression of the nosZ gene and that of the cnorB gene by PCN-1, which led to lower nitrate removal rate (1.67∼6.67 mg L h), higher nitrite accumulation (47.3∼99.8 mg L), and higher NO emission ratios (5∼283 mg L/mg L). Specially, promotion of the nosZ gene expression by increasing Cu(II) concentrations (0∼0.05 mg L) was found, and the absence of Cu resulted in massive NO emission due to poor synthesis of NO reductase. The inhibition effect for both aerobic denitrifying activity and denitrifying gene expression was as follows from strongest to least: Cd(II) (0.5∼2.5 mg L) > Cu(II) (0.5∼5 mg L) > Ni(II) (2∼10 mg L) > Zn(II) (25∼50 mg L). Furthermore, sensitivity of denitrifying gene to heavy metals was similar in order of nosZ > nirS ≈ cnorB > napA. This study is of significance in understanding the potential application of aerobic denitrifying bacteria in practical wastewater treatment.

Cadmium specific proteomic responses of a highly resistantPseudomonas aeruginosasan ai

“…Proteins of denitrication cascade which is not active, obviously, can protect microbial cells against heavy metals. In accordance with our observation Gui et al 45 found that aerobic denitrication was inhibited with heavy metals, including cadmium. Based on the similarity of ionic radii, Cd 2+ probably replaced mercury in mercuric transport protein (MERP).…”

Effects of cobalt-histidine absorbent on aerobic denitrification by Paracoccus versutus LYM

“…2b). This experiment phenomenon, which was similar to that of nitrate aerobic denitrification by Pseudomonas stutzeri PCN-1 under 2.5 mg L −1 Cd(II), 5 mg L −1 Cu(II) or 10 mg L −1 Ni(II) (Gui et al 2017), implied that the CoHis absorbent with a His/Co 2+ of 2 had stronger inhibition effect on the activity of nitrite reductase than of nitrate reductase. In the EG-nitrite, the reduction of nitrite was very slow over the entire experiment, with a final removal efficiency of 13% (Fig.…”

“…When the His/Co 2+ rose to 3, LYM could transfer 96% initial nitrate (150 mg L −1 , 10.7 mM) to nitrite within 6.3 h. As an intermediate of denitrification, nitrite accumulated to as much as 141 mg L −1 in 6.3 h, which was probably caused by the time lag between the highest activity level of nitrate reductase and nitrite reductase (Gui et al 2017). The accumulated nitrite was reduced with a distinctly slower rate than in the CG, and the decrease of accumulated nitrite stopped at 20 mg L −1 after 48 h. The reduction of added nitrite was fast in 0–24 h with a rate slower than in the CG, then slowed down, and finally stopped at 6 mg L −1 after 48 h. The descent of cobalt(II) was fast in 0–6 h and slowed down in the following time, manifesting a plateau in the middle period.…”

“…As there was substantial residual free His in the Co(II)His absorbent, the effects of His on the removal of nitrate and nitrite could not be ignored. In addition, Gui et al (2017) confirms that some heavy metals restrain aerobic denitrifying activity of Pseudomonas stutzeri PCN-1 and lead to the accumulation of nitrous oxide (N 2 O), a potent greenhouse gas (Carreira et al 2017). Thus, the gas product analysis of the aerobic denitrification process under Co(II)His absorbent was also important.…”

Nitrous oxide emissions in soils fertilized with pig manure: soil processes and strategies of control and mitigation

“…Studies in literature show the presence of heavy metals such as zinc (Zn +2 ), nickel (Ni +2 ) and cadmium (Cd +2 ) inhibit the expression of nosZ, especially copper (Cu +2 ) (at concentrations ≥ 0.5 mg L -1 ) (Gui et al, 2017). This gene is responsible for the activation of N2O reductase, an enzyme that catalyzes the reduction of N2O to N2 and is activated by nosZ (Figure 3).…”