New insight into biodegradation mechanism of phenylurea herbicides by cytochrome P450 enzymes: Successive N-demethylation mechanism

A novel micromagnetic carrier-modified integrated fixed-film activated sludge system for simultaneous efficient removal of tetracycline and mitigation of antibiotic resistance genes proliferation and dissemination

To address the challenge of antibiotic-containing wastewater, a novel micromagnetic carrier-modified integrated fixed-film activated sludge system (MC-IFAS) was developed for treating tetracycline (TC)-containing swine wastewater in this study. The magnetic effects of the MC significantly enhanced TC removal by improving TC biosorption and biodegradation in both the suspended activated sludge and the carrier-attached biofilm in the MC-IFAS. The increased electrostatic attraction and number of binding sites in both the activated sludge and the biofilm enhanced their TC biosorption capacities, particularly in the activated sludge. Additionally, the MC shifted microbial community assembly from stochastic to deterministic factors, amplifying the selection pressure induced by TC on the microbial community, thus enriching organic compound-degrading genera Dokdonella and TM7a; it also stimulated ammonia monooxygenase-mediated and cytochrome P450-mediated TC metabolisms and upregulated functional genes encoding lyases, transferases, hydrolases, and oxidoreductases- all of which enhanced TC biodegradation capacity in the MC-IFAS, particularly in the biofilm. While enhancing TC removal efficiency, the MC mitigated the proliferation and dissemination of antibiotic resistance genes (ARGs) by suppressing the abundances of ARGs hosts, the mobile genetic element intI1, and genes encoding ATP-binding cassette transporters and putative transposases. This study provides novel insights into the large-scale applications of magnetic field-enhanced TC removal strategies.

How Rhodococcus ruber accelerated biodegradation of benzophenone-3

Benzophenone-3 (2-hydroxy-4-methoxybenzophenone, BP-3) poses risks to human health and natural ecosystems, and means to improve its biodegradation are necessary. When a small mass of Rhodococcus ruber, isolated from BP-3-acclimated biomass, was bioaugmented into the acclimated biomass, BP-3 removal was accelerated by 120 %. The first step of BP-3 biodegradation generates either 2,5-dihydroxy-4-methoxybenzophenone (5-OH-BP-3) or benzophenone-1 (2,4-dihydoxybenzophenone, BP-1). BP-1 is generated by sequential demethylation, hydroxylation, and dehydrogenation reactions, while 5-OH-BP-3 is generated by one mono-oxygenation reaction. Of the two intermediates, 5-OH-BP-3 exhibited stronger inhibition than BP-1 or the original BP-3. Gene-completion mapping showed that R. ruber contains genes for demethylase, hydrolase, dehydrogenase, and mono-oxygenase reaction, which means that R. ruber could generate the less-toxic BP-1. Thus, bioaugmentation of R. ruber into BP-3-acclimated biomass eliminated the accumulation of 5-OH-BP-3 and, consequently, accelerated of BP-3 biodegradation via BP-1.

Evidence for the formation of 6PPD-quinone from antioxidant 6PPD by cytochrome P450

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) as a rubber antioxidant has attracted global concern, since its ozone-oxidation product 6PPD-quinone (6PPDQ) was found to be the primary toxicant responsible for urban runoff mortality syndrome in coho salmon. However, the biotransformation fate and associated toxicological mechanism of 6PPD have not received much study yet. In this work, the in vitro assays showed 6PPD can be transformed into 6PPDQ by cytochromes P450 (CYP450) in human liver microsomes (HLMs) with 0.98 % production rate, and the adducts of 6PPDQ with calf thymus DNA and the N-N coupling product between 6PPD and 6PPDQ were further identified after 6PPD incubation in HLMs. Further evidence for the 6PPDQ formation can be obtained from the in vivo assays that the 6PPDQ-DNA adducts and 6PPD-N-N-6PPDQ dimer were detected in mice by oral gavage with 6PPD, and the latter dimer species was detected as well in 6PPD exposure to zebrafish larvae. Especially, the bioaccumulation property and high reactivity of 6PPDQ result in the continuous formation of the significant DNA adducts and 6PPD-N-N-6PPDQ dimer even in case of low production rate of biotransformation of 6PPD to 6PPDQ, which may provide potentially effective biomarkers for such process. DFT computations revealed the formation mechanism of 6PPDQ is the (N)H-abstraction of 6PPD by CYP450, followed by amino radical rebound at the nearby ortho-carbon, yielding a quinol intermediate due to spin delocalization, that might readily undergo further oxidation by CYP450 into 6PPDQ.

Biochemical and transcriptomic analyses reveal the toxicological response and potential mechanism of butyl benzyl phthalate in zebrafish gills

Butyl benzyl phthalate (BBP), a common phthalate plasticizer, is frequently detected in aquatic environments. However, there has been relatively little research on its effects on gill-related responses. This study exposed adult zebrafish to BBP concentrations ranging from 5 to 500 μg/L for 28 days, specifically investigating its toxicity in the gills. Assessment of oxidative stress biomarkers and gene expression related to apoptosis and mitochondria was conducted. Results demonstrated that exposure to 500 μg/L of BBP disrupted the antioxidant defense system, leading to lipid peroxidation and DNA damage. Moreover, the expression level of the caspase-3 gene exhibited an approximate two-fold increase, whereas the expression of 18rs-rrn decreased by 50 % on day 28. Gene Ontology enrichment analysis indicated suppressed expression of antioxidant and metabolic process terms, alongside inhibition of metabolism, immune, and signal transduction-related pathways. This study offers novel insights into the toxic effects and mechanisms of BBP on fish, providing valuable data for assessing environmental risks linked to BBP contamination and advocating for its management in aquatic ecosystems.

Efficient degradation of benzalkonium chloride (BAC) by zero-valent iron activated persulfate: Kinetics, reaction mechanisms, theoretical calculations and toxicity evolution

The present study systematically investigated the elimination of benzalkonium chloride (BAC) in the zero valent iron activated persulfate (Fe0/PS) system. The influence of operational parameters, including PS concentration, Fe0 dosage and pH, were investigated through a series of kinetic experiments. When the Fe0 dosage was 5.0 mM, the initial ratio of [PS]: [BAC] was 10:1, the degradation efficiency could achieve 91.7% at pH 7.0 within 60 min. Common inorganic anions and humic acid did not significantly affect BAC degradation, implying that Fe0/PS system had a potential application prospect in the actual wastewater remediation. Based on the electron paramagnetic resonance test and quenching experiments, the BAC degradation was found to be contributed by •OH, SO4•- and Fe(IV). A total of 23 intermediates were identified by the liquid chromatography-mass spectrometry, and the degradation pathways were proposed accordingly, including dealkylation and demethylation, hydroxylation, sulfate substitution and benzyl C-N cleavage reactions. Density functional theory based calculations were conducted to realize the rationality of the proposed reaction mechanisms. The toxicity of transformation products was predicted by ECOSAR program. This work demonstrated the possibility of BAC removal in hospital and municipal wastewater by Fe0/PS treatment, and also provides a safe choice for deep treatment of quaternary ammonium salt wastewater.

Computational simulations uncover enantioselective metabolism of chiral triazole fungicides by human CYP450 enzymes: A case study of tebuconazole

Tebuconazole (TEB), a prominent chiral triazole fungicide, has been extensively utilized for plant pathogen control globally. Despite experimental evidence of TEB metabolism in mammals, the enantioselectivity in the biotransformation of R- and S-TEB enantiomers by specific CYP450s remains elusive. In this work, integrated in silico simulations were employed to unveil the binding interactions and enantioselective metabolic fate of TEB enantiomers within human CYP1A2, 2B6, 2E1, and 3A4. Molecular dynamics (MD) simulations clearly delineated the binding specificity of R- and S-TEB to the four CYP450s, crucially determining their differences in metabolic activity and enantioselectivity. The primary driving force for robust ligand binding was identified as van der Waals interactions with CYP450s, particularly involving the hydrophobic residues. Mechanistic insights derived from quantum mechanics/molecular mechanics (QM/MM) calculations established C2-methyl hydroxylation as the predominant route of R-/S-TEB metabolism, while C6-hydroxylation and triazol epoxidation were deemed kinetically infeasible pathways. Specifically, the resulting hydroxy-R-TEB metabolite primarily originates from R-TEB biotransformation by 1A2, 2E1 and 3A4, whereas hydroxy-S-TEB is preferentially produced by 2B6. These findings significantly contribute to our comprehension of the binding specificity and enantioselective metabolic fate of chiral TEB by CYP450s, potentially informing further research on human health risk assessment associated with TEB exposure.

Remediation of isoproturon-contaminated soil by Sphingobium sp. strain YBL2: Bioaugmentation, detoxification and community structure

The widely used phenylurea herbicide isoproturon (IPU) and its residues can inhibit the growth of subsequently planted crops. However, reports on bioremediation of IPU-contaminated soil are scarce. In this study, Sphingobium sp. strain YBL2-gfp (a derivative of the IPU-degrading Sphingobium sp. strain YBL2 isolated by our lab) was constructed to bioremediate IPU-contaminated soil. In pot experiments, strain YBL2-gfp colonized the roots of wheat and eliminated IPU residues in the soil within 21 d, effectively alleviating its toxicity and restoring wheat growth. IPU treatment reduced the richness and diversity of soil bacteria, while inoculation YBL2-gfp mainly affected richness with less impact on diversity. The high concentrations of IPU and inoculation of YBL2-gfp alone reduced the soil microbial community connections, while bioaugmentation treatment enhanced the soil microbial community connections. Additionally, strain YBL2-gfp stimulated the metabolic capacity of the indigenous microbes, promoting the degradation of IPU and reducing the negative impact of high concentrations of IPU on microbial community. Taken together, this study offers relatively comprehensive insights into the practical application of bioaugmentation, demonstrating that strain YBL2 has the potential to remediate IPU-contaminated soils.

Uptake and Biotransformation of Guvermectin in Three Crops after In Vivo and In Vitro Exposure

Guvermectin, as a novel nucleoside-like biopesticide, could increase the rice yield excellently, but the potential environmental behaviors remain unclear, which pose potential health risks. Therefore, the uptake and biotransformation of guvermectin in three types of crops (rice, lettuce, and carrot) were first evaluated with a hydroponic system. Guvermectin could be rapidly absorbed and reached equilibrium in roots (12-36 h) and shoots (24-60 h) in three plants, and guvermectin was also vulnerable to dissipation in roots (t1/2 1.02-3.65 h) and shoots (t1/2 9.30-17.91 h). In addition, 8 phase I and 2 phase II metabolites, transformed from guvermectin degradation in vivo and in vitro exposure, were identified, and one was confirmed as psicofuranine, which had antibacterial and antitumor properties; other metabolites were nucleoside-like chemicals. Molecular simulation and quantitative polymerase chain reaction further demonstrated that guvermectin was metabolized by the catabolism pathway of an endogenous nucleotide. Guvermectin had similar metabolites in three plants, but the biotransformation ability had a strong species dependence. In addition, all the metabolites exhibit neglectable toxicities (bioconcentration factor <2000 L/kg b.w., LC50,rat > 5000 mg/kg b.w.) by prediction. The study provided valuable evidence for the application of guvermectin and a better understanding of the biological behavior of nucleoside-like pesticides.

Insight into chemically reactive metabolites of aliphatic amine pollutants: A de novo prediction strategy and case study of sertraline

The uncommon metabolic pathways of organic pollutants are easily overlooked, potentially leading to idiosyncratic toxicity. Prediction of their biotransformation associated with the toxic effects is the very purpose that this work focuses, to develop a de novo method to mechanistically predict the reactive toxicity pathways of uncommon metabolites from start aliphatic amine molecules, which employed sertraline triggered by CYP450 enzymes as a model system, as there are growing concerns about the effects on human health posed by antidepressants in the aquatic environment. This de novo prediction strategy combines computational and experimental methods, involving DFT calculations upon sequential growth, in vitro and in vivo assays, dissecting chemically reactive mechanism relevant to toxicity, and rationalizing the fundamental factors. Significantly, desaturation and debenzylation-aromatization as the emerging metabolic pathways of sertraline have been elucidated, with the detection of DNA adducts of oxaziridine metabolite in mice, highlighting the potential reactive toxicity. Molecular orbital analysis supports the reactivity preference for toxicological-relevant C-N desaturation over N-hydroxylation of sertraline, possibly extended to several other aliphatic amines based on the Bell-Evans-Polanyi principle. It was further validated toward some other wide-concerned aliphatic amine pollutants involving atrazine, ε-caprolactam, 6PPD via in silico and in vitro assays, thereby constituting a complete path for de novo prediction from case study to general applications.