Neonicotinoid insecticides are one of the most important commercial insecticides used worldwide. The potential toxicity of the residues present in environment to humans has received considerable attention. In this study, a novel Ochrobactrum sp. strain D-12 capable of using acetamiprid as the sole carbon source as well as energy, nitrogen source for growth was isolated and identified from polluted agricultural soil. Strain D-12 was able to completely degrade acetamiprid with initial concentrations of 0–3000 mg·L⁻¹ within 48 h. Haldane inhibition model was used to fit the special degradation rate at different initial concentrations, and the parameters q_max, K_s and K_i were determined to be 0.6394 (6 h)⁻¹, 50.96 mg·L⁻¹ and 1879 mg·L⁻¹, respectively. The strain was found highly effective in degrading acetamiprid over a wide range of temperatures (25–35°C) and pH (6–8). The effects of co-substrates on the degradation efficiency of acetamiprid were investigated. The results indicated that exogenously supplied glucose and ammonium chloride could slightly enhance the biodegradation efficiency, but even more addition of glucose or ammonium chloride delayed the biodegradation. In addition, one metabolic intermediate identified as N-methyl-(6-chloro-3-pyridyl)methylamine formed during the degradation of acetamiprid mediated by strain D-12 was captured by LC-MS, allowing a degradation pathway for acetamiprid to be proposed. This study suggests the bacterium could be a promising candidate for remediation of environments affected by acetamiprid.

Quizalofop-p-ethyl (QPE) is a post-emergence herbicide that effectively controls grass weeds and is often detected in the environment. However, the biochemical and molecular mechanisms of QPE degradation in the environment remains unclear. In this study, a highly effective QPE-degrading bacterial strain J-2 was isolated from acclimated activated sludge and identified as a Pseudomonas sp., containing the QPE breakdown metabolite quizalofop acid (QA) identified by Liquid Chromatography-Ion Trap-Mass Spectrometry (LC-IT-MSn) analysis. A novel QPE hydrolase esterase-encoding gene qpeH was cloned from strain J-2 and functionally expressed in Escherichia coli BL21 (DE3). The specific activity of recombinant QpeH was 198.9 ± 2.7 U mg−1 for QPE with K m and K cat values of 41.3 ± 3.6 μM and 127.3 ± 4.5 s−1. The optimal pH and temperature for the recombinant QpeH were 8.0 and 30 °C, respectively and the enzyme was activated by Ca2+, Cd2+, Li+, Fe3+ and Co2+ and inhibited by Ni2+, Fe2+, Ag+, DEPC, SDS, Tween 80, Triton X, β-mercaptoethanol, PMSF, and pCMB. In addition, the catalytic efficiency of QpeH toward different AOPP herbicides in descending order was as follows: fenoxaprop-P-ethyl > quizalofop-P-tefuryl > QPE > haloxyfop-P-methyl > cyhalofopbutyl > clodinafop-propargyl. On the basis of the phylogenetic analysis and multiple sequence alignment, the identified enzyme QpeH, was clustered with esterase family V, suggesting a new member of this family because of its low similarity of amino acid sequence with esterases reported previously.

Denitrification is an important microbial process in soils and leads to the emission of nitrous oxide (N₂O). However, studies about the microbial community involved in denitrification processes in polluted paddy fields are scarce. Here, we studied two rice paddies which had been polluted for more than three decades by metal mining and smelter activities. Abundance and community composition were determined using real-time polymerase chain reaction (PCR) assay and denaturing gradient gel electrophoresis of nitrite reductase and nitrous oxide reductase gene amplicons (nirK and nosZ), while denitrifying activities were assessed by measuring potential denitrifier enzyme activity. We found that the community structure of both nirK and nosZ containing denitrifiers shifted under pollution in the two rice paddies. All the retrieved nirK sequences did not group into either α- or β-proteobacteria, while most of the nosZ species were affiliated with α-proteobacteria. While the abundance of both nirK and nosZ was significantly reduced in the polluted soils at “Dexing” (with relatively higher Cu levels), these parameters did not change significantly at “Dabaoshan” (polluted with Cd, Pb, Cu, and Zn). Furthermore, total denitrifying activity and N₂O production and reduction rates also only decreased under pollution at “Dexing.” These findings suggest that nirK and nosZ containing denitrifier populations and their activities could be sensitive to considerable Cu pollution, which could potentially affect N₂O release from polluted paddy soils.