Flonicamid (N-cyanomethyl-4-trifluoromethylnicotinamide, FLO) is a new type of pyridinecarboxamide insecticide that exhibits particularly good efficacy in pest control. However, the extensive use of ...FLO in agricultural production poses environmental risks. Hence, its environmental behavior and degradation mechanism have received increasing attention. Microvirga flocculans CGMCC 1.16731 rapidly degrades FLO to produce the intermediate N-(4-trifluoromethylnicotinoyl) glycinamide (TFNG-AM) and the end acid metabolite 4-(trifluoromethyl) nicotinol glycine (TFNG). This bioconversion is mediated by the nitrile hydratase/amidase system; however, the amidase that is responsible for the conversion of TFNG-AM to TFNG has not yet been reported. Here, gene cloning, overexpression in Escherichia coli and characterization of pure enzymes showed that two amidases—AmiA and AmiB—hydrolyzed TFNG-AM to TFNG. AmiA and AmiB showed only 20–30% identity to experimentally characterized amidase signature family members, and represent novel amidases. Compared with AmiA, AmiB was more sensitive to silver and copper ions but more resistant to organic solvents. Both enzymes demonstrated good pH tolerance and exhibited broad amide substrate specificity. Homology modeling suggested that residues Asp191 and Ser195 may strongly affect the catalytic activity of AmiA and AmiB, respectively. The present study furthers our understanding of the enzymatic mechanisms of biodegradation of nitrile-containing insecticides and may aid in the development of a bioremediation agent for FLO.
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•This is the first report on amidases involved in microbial metabolism of FLO.•M. flocculans efficiently degrades insecticide FLO via the NHase/amidase pathway.•AmiA and AmiB show less than 30% identities to other reported characterized amidases.•AmiA and AmiB exhibited good thermal stability and broad substrate specificity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The insecticide imidacloprid (IMI), which is used worldwide, pollutes environments and has significant ecotoxicological effects. Microbial metabolism and photolysis are the major pathways of IMI ...degradation in natural environments. Several studies have reported that the metabolites of IMI nitroreduction are more toxic to some insects and mammals than IMI itself. Thus, environmental degradation of IMI may enhance the ecotoxicity of IMI and have adverse effects on non-target organisms. Here, we report that an actinomycete—Gordonia alkanivorans CGMCC 21704—transforms IMI to a nitroreduction metabolite, nitroso IMI. Resting cells of G. alkanivorans at OD600 nm = 10 transformed 95.7% of 200 mg L−1 IMI to nitroso IMI in 4 d. Nitroso IMI was stable at pH 4–9. However, it rapidly degraded under sunlight via multiple oxidation, dehalogenation, and oxidative cleavage reactions to form 10 derivatives; the half-life of nitroso IMI in photolysis was 0.41 h, compared with 6.19 h for IMI. Acute toxicity studies showed that the half maximal effective concentration (EC50) values of IMI, nitroso IMI, and its photolytic metabolites toward the planktonic crustacean Daphnia magna for immobilization (exposed to the test compounds for 48 h) were 17.70, 9.38, 8.44 mg L−1, respectively. The half-life of nitroso IMI in various soils was also examined. The present study reveals that microbial nitroreduction accelerates IMI degradation and the nitroso IMI is easily decomposed by sunlight and in soil. However, nitroso IMI and its photolytic products have higher toxicity toward D. magna than the parent compound IMI, and therefore increase the ecotoxicity of IMI.
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•A new isolate Gordonia alkanivorans effectively transformed IMI to nitroso derivate.•The genome of G. alkanivorans CGMCC 21704 has been determined.•The nitroso IMI is easily degraded by photolysis and in soils.•10 derivates were produced under photolysis by sunlight.•Nitroso IMI and its photolytic products were more toxic to D. magna than IMI.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Flonicamid (N-cyanomethyl-4-trifluoromethylnicotinamide, FLO) is a new type of pyridinamide insecticide that regulates insect growth. Because of its wide application in agricultural production and ...high solubility in water, it poses potential risks to aquatic environments and food chain. In the present study, Ensifer adhaerens CGMCC 6315 was shown to efficiently transform FLO into N-(4-trifluoromethylnicotinoyl) glycinamide (TFNG-AM) via a hydration pathway mediated by two nitrile hydratases, PnhA and CnhA. In pure culture, resting cells of E. adhaerens CGMCC 6315 degraded 92% of 0.87 mmol/L FLO within 24 h at 30 degreesC (half-life 7.4 h). Both free and immobilized (by gel beads, using calcium alginate as a carrier) E. adhaerens CGMCC 6315 cells effectively degraded FLO in surface water. PnhA has, to our knowledge, the highest reported degradation activity toward FLO, V.sub.max = 88.7 U/mg (K.sub.m = 2.96 mmol/L). Addition of copper ions could increase the enzyme activity of CnhA toward FLO by 4.2-fold. Structural homology modeling indicated that residue beta-Glu56 may be important for the observed significant difference in enzyme activity between PnhA and CnhA. Application of E. adhaerens may be a good strategy for bioremediation of FLO in surface water. This work furthers our understanding of the enzymatic mechanisms of biodegradation of nitrile-containing insecticides and provides effective transformation strategies for microbial remediation of FLO contamination.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Two new isocoumarins, (3R)-methyl-8-hydroxy-6-(hydroxymethyl)-7-methoxydihydroisocoumarin (
1
) and (3R)-methyl-7,8-dimethoxy-6-(hydroxymethyl)dihydroisocoumarin (
2
), together with three known ...isocoumarins (
3
–
5
), were isolated from the fermentation products of an endophytic fungus Aspergillus versicolor. Their structures were elucidated by spectroscopic methods, including extensive 1D and 2D NMR techniques. The anti-tobacco mosaic virus (anti-TMV) activities of compounds
1
and
2
were evaluated. Compounds
1
and
2
showed anti-TMV activities with inhibition rates of 21.8 and 18.6% at the concentration of 20 μM, respectively.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Three new isocoumarins, terrecoumarins A–C (1–3), together with six known isocoumarins (4–9) were isolated from the fermentation products of the fungus Penicillium oxalicum 0403. Their structures ...were elucidated by spectroscopic methods, including extensive 1D and 2D NMR techniques. The anti-tobacco mosaic virus (anti-TMV) activities of 1 – 9 were evaluated. The results revealed that compound 1 showed high anti-TMV activity with inhibition rate 25.4 ± 3.5%. Other compounds also showed weak activity with inhibition rate in the range of 11.3–18.9%.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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