Deamination is ubiquitous in nature and has important biological significance. Leucobacter triazinivorans JW-1, recently isolated from sludge, can rapidly degrade s-triazine herbicides. The responsible enzymes, however, have not been purified and characterized.Herein, we purified an amidohydrolase, i.e., N-isopropylammelide isopropylaminohydrolase (AtzC) from JW-1 cells by ammonium sulfate precipitation and three chromatography steps. The purified AtzC catalyzed amidohydrolysis of N-isopropylammelide to cyanuric acid. The optimal catalytic conditions of the purified AtzC were 42 °C and pH 7.0, and the Kₘ and Vₘₐₓ of AtzC was 0.811 mM and 28.19 mmol/min·mg. AtzC could catalyze amidohydrolysis of an N-alkyl substituent from dihydroxy s-triazines to cyanuric acid. Molecular docking and structural alignments were used to infer AtzC catalytic mechanism. The structural architecture of AtzC resembled that of cytosine deaminase in class III amidohydrolase, with a single Zn²⁺ coordinated by His and Asp. Interestingly, the AtzC lacks an acidic residue putatively to activate water for hydrolysis as compared to the other amidohydrolases. His253 in AtzC probably functions as a single general acid-base catalyst. These findings further enhance our understanding how aminohydrolases catalyze the metabolism of s-triazine herbicides.

Antibiotics can effectively protect livestock from pathogen infection, but residual antibiotics in manure bring risks to ecosystems and public health. Here, we demonstrated that black soldier fly larvae (BSFL) could provide an environmentally friendly manure treatment based on their ability to effectively and rapidly degrade tetracycline (TC). Investigation of the biological mechanisms and degradation pathways of TC by BSFL indicated that nearly 97% of TC was degraded within 12 days in a non-sterile BSFL treatment system, which is up to 1.6-fold faster than that achieved by normal composting. Our results showed that rapid TC-degradation was largely carried out by the intestinal microbiota of the larvae, which doubled the TC-degradation rates compared to those achieved in sterile BSFL systems. This conclusion was further supported by highly-efficient TC-biodegradation both in vivo and in vitro by four larval intestinal isolates. Moreover, detailed microbiome analysis indicated that intestinal bacterial and fungal communities were modified along with significantly increased tet gene copy number in the gut, providing the means to tolerate and degrade TC. Through analysis of TC degradation in vitro, four possible biodegradation products, two hydrolysis products and three conceivable inactivation products were identified, which suggested TC degradation reactions including hydrolysis, oxygenation, deamination, demethylation, ring-cleavage, modification, etc. In conclusion, our studies suggested an estimation of the fate of TC antibiotics in manure treatment by BSFL colonized by gut microbes. These results may provide a strategy for accelerating the degradation of antibiotics by adjusting the intestinal microbiota of BSFL.

The aim of the present study is to investigate the effects of operating conditions and establish the mechanism of xanthene dye removal from aqueous solutions by electrocoagulation (EC) using a batch-stirred cell operated under galvanostatic regime. The influence of the operating parameters such as: initial pH and dye concentration, electrolysis time, current density, electrode configuration, and electrical current type on the EC performances was investigated. EC tests were performed at current density values ranging from 45 to 109 A/m, initial dye concentrations ranged between 0.1 and 1 g/L, and initial pH values adjusted in the range from 3 to 9. The effects of several electrode configurations (aluminum–aluminum, mild steel–mild steel, and aluminum–mild steel) and current regimes (direct current and alternating pulsed current) on the removal efficiency and energy and material consumption are also discussed. Total organic carbon (TOC) analysis, UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry (CV) were employed in order to elucidate the decolorization mechanism of Rhodamine 6G (R6G) dye by EC in aqueous solutions. With this aim in view, chemical coagulation tests were also carried out. The best performance was obtained when the EC process was conducted with iron-based electrode configuration in alternative pulse current (APC) mode. It was found that the removal of R6G is due to the co-precipitation of polymeric iron flocs with the phenyl-xanthene radicals remained in the bulk solution after the demethylation and deamination processes. Furthermore, the flocs are separated by flotation with the support of the molecular hydrogen generated at the cathode (in particular at relatively high values of current density) or by sedimentation.

Fludioxonil is a post-harvest fungicide contained in effluents produced by fruit packaging plants, which should be treated prior to environmental dispersal. We developed and evaluated an immobilized cell bioreactor, operating under microaerophilic conditions and gradually reduced hydraulic retention times (HRTs) from 10 to 3.9 days, for the biotreatment of fludioxonil-rich wastewater. Fludioxonil removal efficiency was consistently above 96%, even at the shortest HRT applied. A total of 12 transformation products were tentatively identified during fludioxonil degradation by using liquid chromatography coupled to quadrupole time-of-flight Mass spectrometry (LC-QTOF-MS). Fludioxonil degradation pathway was initiated by successive hydroxylation and carbonylation of the pyrrole moiety and disruption of the oxidized cyanopyrrole ring at the NH-C bond. The detection of 2,2-difluoro-2H-1,3-benzodioxole-4-carboxylic acid verified the decyanation and deamination of the molecule, whereas its conversion to the tentatively identified compound 2,3-dihydroxybenzoic acid indicated its defluorination. High-throughput amplicon sequencing revealed that HRT shortening led to reduced α-diversity, significant changes in the β-diversity, and a shift in the bacterial community composition from an initial activated sludge system typical community to a community composed of bacterial taxa like Clostridium, Oligotropha, Pseudomonas, and Terrimonas capable of performing advanced degradation and/or aerobic denitrification. Overall, the immobilized cell bioreactor operation under microaerophilic conditions, which minimizes the cost for aeration, can provide a sustainable solution for the depuration of fludioxonil-contaminated agro-industrial effluents.

In this work, the effect of supporting electrolytes on the simultaneous electrochemical oxidation of the pharmaceuticals sulfamethoxazole (SMX), propranolol (PRO), and carbamazepine (CBZ) in aqueous solutions has been studied. Based on the identified by-products, the degradation mechanisms were proposed and the acute toxicity was evaluated for each electrolyte. Assays were carried out in batch mode in a 2 L undivided reactor using a niobium coated with boron-doped diamond (Nb/BDD) mesh anode and Ti cathode at 2.5 A in presence of different supporting electrolytes (Na₂SO₄, NaCl, or NaBr) at the same concentration of 7 mM. The degradation rates were higher in the assays with NaCl and NaBr. Reaction by-products were identified by gas chromatography–mass spectrometry. Indirect oxidation by electrogenerated reactive halogen species (RHS) was the main mechanism when halide ions were used as electrolytes. Ten by-products were detected using Na₂SO₄ as electrolyte, while 19 (12 non-halogenated and 7 halogenated) and 20 (10 non-halogenated and 10 halogenated) using NaCl and NaBr respectively. The proposed degradation pathways involve transformation (hydroxylation, deamination, desulfonation, and halogenation) and bond rupture to produce less molecular weight compounds and their further transformation until total degradation. Chlorinated and brominated by-products confirm halogenation reactions. The electrogenerated RHS presented a significant inhibition effect on Vibrio fischeri; nevertheless, acute toxicity was not presented using Na₂SO₄ as electrolyte and a pharmaceutical concentration of 5 μg/L. In this view, the role of the supporting electrolyte in electrochemical oxidation process is crucial since it strongly influence degradation rate, by-products, and acute toxicity.

Handling of two nitro-aromatic compounds, 4-nitroaniline (4NA) and 4-nitrophenol (4NP), simultaneously by Chlorella pyrenoidosa was investigated. Algae would secrete or degrade nitro-aromatic compounds depending on different environmental conditions, in which the mode of handling was determined by the relative formation and degradation rate of the compound. Repeated intermittent trigger with externally added 4NA would induce the continuous secretion of 4NA by algae. Simultaneous exposure of both 4NA and 4NP to algae at normal condition would induce the algae to secrete both compounds. An increase in 4NA exposure concentration would elevate both 4NA and 4NP secretion, and that would be inhibited by the stress conditions of starving or lack of oxygen. Increased 4NA degradation per production rate induced by starving or lack of oxygen might explain the subsequent decrease in 4NA secretion in the presence of 4NP in algae. For 4NP in the presence of 4NA, secretion at normal condition was completely stopped and turned to degradation mode in stress conditions. The decreased formation and increased degradation of 4NP during starving for replenishing energy would explain the net degradation of 4NP in starving condition. The condition of lack of oxygen would inhibit the 4NP formation from 4NA via oxidative deamination, while the degradation of 4NP might not be significantly affected because alternative pathway of degradation via nitro-reduction was available. It may lead to the degradation rate exceeding the formation and explain the net degradation of 4NP in the condition of lack of oxygen.

Certain aromatic amines generated by the decolorization of some azo dyes are not removed substantially by conventional anaerobic–aerobic biotreatment. These aromatic amines are potentially toxic and often released in the wastewater of industrial plants. In this study, the fate and transformation of the naphthylaminesulfonic azo dye Reactive Black 5 (RB5) during different phases of a sequencing batch reactor were investigated. The major products of RB5 decolorization during the anaerobic phase include 2-[(4-aminophenyl)sulfonyl]ethyl hydrogen sulfate (APSEHS) and 1-2-7-triamino-8-hydroxy-3-6-naphthalinedisulfate (TAHNDS). During the aerobic phase, APSEHS was hydrolyzed and produced 4-aminobenzenesulfonic acid, which was further degraded via dearomatization. TAHNDS was transformed rapidly via auto-oxidation into TAHNDSDP₋₁and TAHNDSDP₋₂, which were not further removed by the activated sludge during the entire 30-day aerobic phase. In contrast, different behaviors of TAHNDS were observed during the anoxic phase. The transformation of TAHNDS was initiated either by deamination or desulfonation reaction. TAHNDS was then converted into 3,5-diamino-4-hydroxynaphthalene-2-sulfonic acid, which was subsequently removed via ring cleavage reaction under aerobic condition. In conclusion, complete degradation of TAHNDS by activated sludge occurs only during anoxic/aerobic processes instead of the conventional anaerobic/aerobic processes.

In the present study, oxido-reductive degradation of diazo dye, Direct Red 23, has been carried out by Ziziphus mauritiana peroxidases (specific activity 17.6 U mg⁻¹). Peroxidases have been immobilized via simple adsorption and cross-linking by glutaraldehyde; adsorbed and cross-linked enzyme retained 94.28% and 91.23% of original activity, respectively. The stability of peroxidases was enhanced significantly upon immobilization; a marked widening in both pH and temperature activity profiles were observed. Adsorbed peroxidases exhibited similar pH and temperature optima as reported for the free enzyme. Thermal stability was significantly enhanced in case of cross-linked enzyme which showed 80.52% activity even after 2 h of incubation at 60 °C. Packed bed reactors containing adsorbed and cross-linked peroxidases were run over a period of 4 weeks; adsorbed peroxidases retained 52.86% activity whereas cross-linked peroxidases maintained over 77% dye decolorization ability at the end of the fourth week of its continuous operation. Gas chromatography coupled with mass spectrometry was used to analyze the degradation products; it showed the presence of four major metabolites. Degradation of dye starts with the 1-Hydroxybenzotriazole radical attack on the carbon atom of the phenolic ring bearing azo linkage, converting it into cation radical which underwent nucleophilic attack by a water molecule and results in cleavage of chromophore via symmetric and asymmetric cleavage pathways. Intermediates undergo spontaneous removal of nitrogen, deamination, and oxidation reactions to produce maleic acid as the final degradation product. Graphical abstract