A newly isolated and rapid denitrifier Pseudomonas citronellolis WXP-4: difference in N2O emissions under aerobic and anaerobic conditions.

A novel and efficient facultative anaerobic denitrifying bacterium was isolated and identified as Pseudomonas citronellolis WXP-4. The strain WXP-4 could achieve 100% nitrate and nitrite removal efficiency utilizing sodium succinate as a carbon source, C/N ratio 7, pH 7.0, and temperature 40 °C under both aerobic and anaerobic conditions. The bacterium could tolerate a wide range of NO3--N concentrations from 100 to 1000 mg/L with a maximum nitrogen removal rate of 32.05 mg/(L h). An interesting phenomenon was found that no N2O emission occurred during the denitrifying process under anaerobic conditions, while there was 0.06 mg/L under aerobic conditions. This phenomenon had been confirmed by fluorescence quantitative PCR and the results showed that the relative abundance of nosZ gene increased by 17-fold based on the ratio of anaerobic to aerobic, and thus, nosZ gene could encode more nitrous oxide reductase to accelerate the conversion of N2O under anaerobic conditions. Moreover, the narG, nirK, and norB genes were also identified in the denitrifying pathway of the strain WXP-4. This investigation has demonstrated enormous potential for the future application in wastewater treatment systems.

Simultaneous removal of SO2 and NO by FeII(EDTA) solution: promotion of Mn powder and mechanism of reduction.

The effect of Mn powder addition on the simultaneous removal of SO2 and NO coupled with FeII(EDTA) absorption was investigated in this work. In the NO absorption system with FeII(EDTA), SO2 reduced FeII(EDTA)-NO to FeII(EDTA) with a reduction efficiency reaching 88.5% under the conditions of 4000 mg/m3 SO2, pH 8.0, 44 °C, and the flow rate of 1.2 L/min within 60 min. Introducing 0.1 M Mn powder with SO2 increased the FeII(EDTA)-NO reduction efficiency to 96.8% within 5 min. SO2 was also removed by reducing FeII(EDTA)-NO and converted into SO42- at a removal efficiency of 100%. After adding Mn powder, NO was removed through the following reaction: [Formula: see text]. Mn powder functioned as a reductant to regenerate the absorption of solution, and the coordinated NO in FeII(EDTA)-NO was reduced to NH4+. The resource utilization rate of N reached approximately 77.2%. The integrated technology is a potential solution for flue gas treatment in industrial sectors with coal-fired power plants and industrial boiler. Graphical abstract.

Gene cloning, expression, and reducing property enhancement of nitrous oxide reductase from Alcaligenes denitrificans strain TB.

Nitrous oxide (N2O) is a potent greenhouse gas and tends to accumulate as an intermediate in the process of bacteria denitrification. To achieve complete reduction of nitrogen oxide (NOx) in bacteria denitrification, the structural gene nosZ encoding nitrous oxide reductase (N2OR) was cloned from Alcaligenes denitrificans strain TB (GenBank JQ044686). The recombinant plasmid containing the nosZ gene was built, and the expression of nosZ gene in Escherichia coli was determined. Results show that the nosZ gene consisting of 1917 nucleotides achieves heterologous expression successfully by codon optimization strategy under optimal conditions (pre-induction inoculum OD600 of 0.67, final IPTG concentration of 0.5 mM, inducing time of 6 h, and inducing temperature of 28 °C). Determination result of gas chromatography confirms that N2O degradation efficiency of recombinant E. coli is strengthened by at least 1.92 times compared with that of original strain TB when treated with N2O as substrate. Moreover, N2OR activity in recombinant strain is 2.09 times higher than that in wild strain TB, which validates the aforementioned result and implies that the recombinant E. coli BL21 (DE3)-pET28b-nosZ is a potential candidate to control N2O accumulation and alleviate greenhouse effect. In addition, the N2OR structure and the possible N2O binding site in Alcaligenes sp. TB are predicted, which open an avenue for further research on the relationship between N2OR activity and its structure.