Degradation Of Indole Research Articles

Construction of bienzyme-inorganic hybrid nanoflowers as a high-efficiency biocatalyst for the degradation of indole

Compared to traditional enzyme immobilization techniques, organic-inorganic hybrid nanoflowers (HNFs) are an effective method for enzyme immobilization that can enhance the stability and catalytic activity of free enzymes. Therefore, in this study, glucose oxidase (GOD) and horseradish peroxidase (HRP) were used as the organic components, phosphate copper was used as the inorganic component, and a bienzyme-inorganic hybrid nanoflowers biocatalyst (referred to as biE-HNFs) was prepared using a co-milling self-assembly growth method. The biE-HNFs exhibited complete flower-shaped morphology, the largest specific surface area, highest enzyme activity, and highest loading enzyme concentration when the bienzyme concentration was 1.0 mg mL–1, incubation time was 72 h, HRP-GOD bienzyme concentration ratio was 2:1, phosphate-buffered saline solution (PBS) concentration was 0.10 M and Cu2+ concentration was 0.12 M. Furthermore, compared to free bienzyme, biE-HNFs demonstrated better temperature stability, pH stability, and storage stability. Even after 60 days of storage, the indole degradation rate remained above 90 %. Using organic-inorganic hybrid nanoflowers for immobilizing bienzyme not only retains the advantages of high activity and large specific surface area, but also allows for synergistic effects between HRP-GOD bienzyme in indole degradation, suggesting a new approach for efficient removal of indole by immobilizing bienzyme.

A novel bio-photocatalytic system for efficient degradation of indole by Bi2WO6-Ni-DA@HRP photoperoxidase microspheres

The photoperoxidase microspheres Bi2WO6-Ni-DA@HRP were prepared by covalent binding under the action of electrostatic adsorption for the first time. It was achieved that horseradish peroxidase (HRP) was immobilized on the Bi2WO6via the self-polymerization of dopamine (DA). In this bio-photocatalytic system, the free radicals produced in situ on the surface of Bi2WO6 can activate HRP and induce the photo-enzyme synergistic catalysis function. The interfacial binding force between HRP and the photocatalyst significantly enhanced the electron conduction effect, which improved the separation efficiency and mobility of photogenerated electron-holes, and thus the catalytic effect was improved successfully. Compared with Bi2WO6 and free HRP, Bi2WO6-Ni-DA@HRP under no-added H2O2 have exhibited excellent catalytic activity for indole. The degradation efficiency reached 99.9 % for 20 mg·L−1 indole solution treated with Bi2WO6-Ni-DA@HRP for 210 min under visible light initiation. The free radical trapping experiment showed that holes (h+) and ·OH were the main active substances in the catalytic process. The photoperoxidase catalyst constructed in this study proposed a novel practical approach for the degradation of indole in water and significantly improved the application of HRP in water treatment.

Mechanistic insights of efficient aromatic organic compounds oxidation using biochar derived from coking wastewater sludge

Coking wastewater sludge possessed potential environmental hazards and pyrolysis was a desirable approach which could converted it into one functional carbonous material. The sludge-based biochar (SC-N3) originated from the feedstock of sludge from the regenerated water treatment had various iron-containing species and exhibited the effective catalytic ability. Compared with the degradation of the four pollutants (i.e., phenol, pyridine, quinoline and indole) alone, the mixed of the four pollutants in simulated coking wastewater exhibited a prominent different degradation trend, where the removal rates of indole and quinoline were enhanced from 45% and 30% to 98.9% and 82.3%, respectively. The quinone intermediates from phenol degradation, played a critical role in enhancing the removal rates of indole and quinoline as the electron transfer medium. Both the free radical pathway dominated by •OH and non-radical pathway with 1O2 play the main role in indole degradation, while •OH was the main factor in the catalytic degradation of phenol, quinoline and pyridine. By analysis the intermediates elucidated by Fourier transform ion cyclotron resonance mass spectrometry and three-dimensional excitation-emission matrix fluorescence spectra, the degradation molecular characteristics and pathways of the four pollutants in simulated coking wastewater were deciphered. The findings indicated that the catalyst SC-N3 prepared from the coking wastewater sludge presented unique catalytic properties and possessed a promising application in the degradation of refractory wastewater.

Synthesis of potassium-modified g-C3N4/LaFeO3 nanocomposites as efficient visible-light photocatalytic for indole degradation

A composite photocatalyst KCN/LFO was synthesized using K-modified g-C3N4 (KCN) and LaFeO3 (LFO). The photocatalytic activity of the KCN/LFO was evaluated by degrading indole (heterocyclic organic compound). The KCN/LFO-10 (mass fraction of LaFeO3 with 10%) displayed the highest removal rate of indole. Indole was degraded to 97.366% after 60 min. The photocurrent and electrochemical impedance spectroscopy (EIS) results suggested that the close correlation between KCN and LaFeO3 can increasing the efficiency of photogenerated carrier separation. The capture experiment results demonstrated that ·O2− and ·OH is primary active substance, respectively. Moreover, the degradation efficiency of KCN/LFO-10 to indole remains stable at 87% after four successive experiments of indole photocatalytic degradation. This work presents an effective method for addressing the pollution caused by heterocyclic organic compound.

Influence of Different Plant Extracts on CYP-Mediated Skatole and Indole Degradation in Pigs.

One of the primary substances responsible for the unpleasant odor in boar meat is skatole. Enzymes belonging to the cytochrome P450 (CYP) family play a pivotal role in the hepatic clearance of skatole. This study aimed to investigate the impact of oregano essential oil (OEO), Schisandra chinensis extract (SC), and garlic essential oil (GEO) on hepatic CYP2E1 and CYP2A activity in pigs. In three consecutive trials, cannulated castrated male pigs were provided with a diet containing 0.2-0.3% of one of these plant extracts. Following a 14-day feeding period, the animals were slaughtered, and liver and fat samples were collected. The findings indicate that the activities of CYP2E1 were unaffected by any treatment. However, GEO treatment demonstrated a significant reduction in CYP2A activity (p < 0.05). Pigs treated with GEO also exhibited a notable increase in skatole concentrations in both plasma and adipose tissue. In contrast, animals fed SC displayed elevated skatole concentrations in plasma but not in fat tissue. OEO did not influence skatole concentrations in either blood or fat. Furthermore, the study revealed that a supplementation of 6 g GEO per animal per day induced a significant increase in skatole concentrations in blood plasma within 24 h.

Visible-light-driven photo-peroxidase catalysis: high-efficiency degradation of indole in water.

The demand for H2O2 restricts the wider application of horseradish peroxidase (HRP) in degradation. In this work, a novel photoenzyme synergistic catalytic system was developed for high-efficiency degrading of indole in water by HRP without extra H2O2. The HRP was immobilized on CN-ZIF prepared by the combination of g-C3N4 and ZIF-8 to achieve photo-peroxidase catalyst HRP/Zn-CN-ZIF. Under visible light, photogenerated electrons and H2O2 from HRP/Zn-CN-ZIF participated in the biocatalytic cycle of HRP directly. As a result, the indole at 20 mg L-1 in water was degraded completely in 2 h by the HRP/Zn-CN-ZIF photoenzyme synergistic catalytic system without the addition of H2O2. Furthermore, HRP/Zn-CN-ZIF exhibited superior visible light absorption and charge transfer ability compared to g-C3N4. The results of the mechanism studies suggest that ·OH would play the most significant role from the HRP/Zn-CN-ZIF in indole degradation. This research provides an efficient approach for the removal of indole from water environments.

Degradation of indole via a two-component indole oxygenase system from Enterococcus hirae GDIAS-5

Animal farming copiously generates indoles, which contribute to odor and pose a challenge for deodorization. While biodegradation is widely accepted, there is a lack of suitable indole-degrading bacteria for animal husbandry. In this study, we aimed to construct genetically engineered strains with indole-degrading abilities. Enterococcus hirae GDIAS-5 is a highly efficient indole-degrading bacterium, which functions via a monooxygenase YcnE presumably contributes to indole oxidation. However, the efficiency of engineered Escherichia coli expressing YcnE for indole degradation is lower than that of GDIAS-5. To improve its efficacy, the underlying indole-degradation mechanisms in GDIAS-5 were analyzed. An ido operon that responds to a two-component indole oxygenase system was identified. In vitro experiments showed that the reductase component of YcnE, YdgI, can improve the catalytic efficiency. The reconstruction of the two-component system in E. coli exhibited higher indole removal efficiency than GDIAS-5. Furthermore, isatin, the key intermediate metabolite in indole degradation, might be degraded via a novel isatin-acetaminophen-aminophenol pathway involving an amidase whose coding gene is located near the ido operon. The two-component anaerobic oxidation system, upstream degradation pathway, and engineering strains investigated in this study provide important insights into indole degradation metabolism and offer efficient resources for achieving bacterial odor elimination.

Functional genomic analysis of an efficient indole degrading bacteria strain Alcaligenes faecalis IITR89 and its biodegradation characteristics.

Indole is a nitrogenous heterocyclic aromatic pollutant often detected in various environments. An efficient indole degrading bacterium strain IITR89 was isolated from River Cauvery, India, and identified as Alcaligenes faecalis subsp. phenolicus. The bacterium was found to degrade ~ 95% of 2.5mM (293.75mg/L) of indole within 18h utilizing it as a sole carbon and energy source. Based on metabolite identification, the metabolic route of indole degradation is indole → (indoxyl) → isatin → (anthranilate) → salicylic acid → (catechol) → (Acetyl-CoA) → and further entering into TCA cycle. Genome sequencing of IITR89 revealed the presence of gene cluster dmpKLMNOP, encoding multicomponent phenol hydroxylase; andAbcd gene cluster, encoding anthranilate 1,2-dioxygenase ferredoxin subunit (andAb), anthranilate 1,2-dioxygenase large subunit (andAc), and anthranilate 1,2-dioxygenase small subunit (andAd); nahG, salicylate hydroxylase; catA, catechol 1,2-dioxygenase; catB, cis, cis-muconate cycloisomerase; and catC, muconolactone D-isomerase which play an active role in indole degradation. The findings strongly support the degradation potential of strain IITR89 and its possible application for indole biodegradation.

Identification of an indole biodegradation gene cluster from Providencia rettgeri and its contribution in selectively biosynthesizing Tyrian purple.

Tyrian purple, mainly composed of 6, 6'-dibromoindigo, is a precious dye extracted from sea snails. In this study, we found Tyrian purple can be selectively produced by a bacterial strain GS-2 when fed with 6-bromotryptophan in the presence of tryptophan. This GS-2 strain was then identified as Providencia rettgeri based on bacterial genome sequencing analysis. An indole degradation gene cluster for indole metabolism was identified from this GS-2 strain. The heterologous expression of the indole degradation gene cluster in Escherichia coli BL21 (DE3) and in vitro enzymatic reaction demonstrated that the indole biodegradation gene cluster may contribute to selectively biosynthesizing Tyrian purple. To further explore the underlying mechanism of the selectivity, we explored the intermediates in this indole biodegradation pathway using liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS/MS), which indicated that the indole biodegradation pathway in Providencia rettgeri is the catechol pathway. Interestingly, the monooxygenase GS-C co-expressed with its corresponding reductase GS-D in the cluster has better activity for the biosynthesis of Tyrian purple compared with the previously reported monooxygenase from Methylophaga aminisulfidivorans (MaFMO) or Streptomyces cattleya cytochrome P450 enzyme (CYP102G4). This is the first study to show the existence of an indole biodegradation pathway in Providencia rettgeri, and the indole biodegradation gene cluster can contribute to the selective production of Tyrian purple.

Indole and p-cresol in feces of healthy subjects: Concentration, kinetics, and correlation with microbiome.

Indole and p-cresol are precursors of the most important uremic toxins, generated from the fermentation of amino acids tryptophan and tyrosine by the proteolytic community of intestinal bacteria. The present study focused on the relationship between the microbiome composition, the fecal levels of indole and p-cresol, and their kinetics of generation/degradation in fecal cultures. The concentration of indole and p-cresol, the volatilome, the dry weight, and the amount of ammonium and carbohydrates were analyzed in the feces of 10 healthy adults. Indole and p-cresol widely differed among samples, laying in the range of 1.0-19.5μg/g and 1.2-173.4μg/g, respectively. Higher fecal levels of indole and p-cresol were associated with lower carbohydrates and higher ammonium levels, that are markers of a more pronounced intestinal proteolytic metabolism. Positive relationship was observed also with the dry/wet weight ratio, indicator of prolonged intestinal retention of feces. p-cresol and indole presented a statistically significant negative correlation with OTUs of uncultured Bacteroidetes and Firmicutes, the former belonging to Bacteroides and the latter to the families Butyricicoccaceae (genus Butyricicoccus), Monoglobaceae (genus Monoglobus), Lachnospiraceae (genera Faecalibacterium, Roseburia, and Eubacterium ventriosum group). The kinetics of formation and/or degradation of indole and p-cresol was investigated in fecal slurries, supplemented with the precursor amino acids tryptophan and tyrosine in strict anaerobiosis. The presence of the precursors bursted indole production but had a lower effect on the rate of p-cresol formation. On the other hand, supplementation with indole reduced the net rate of formation. The taxa that positively correlated with fecal levels of uremic toxins presented a positive correlation also with p-cresol generation rate in biotransformation experiments. Moreover other bacterial groups were positively correlated with generation rate of p-cresol and indole, further expanding the range of taxa associated to production of p-cresol (Bacteroides, Alistipes, Eubacterium xylanophylum, and Barnesiella) and indole (e.g., Bacteroides, Ruminococcus torques, Balutia, Dialister, Butyricicoccus). The information herein presented contributes to disclose the relationships between microbiota composition and the production of uremic toxins, that could provide the basis for probiotic intervention on the gut microbiota, aimed to prevent the onset, hamper the progression, and alleviate the impact of nephropaties.

Photoelectrochemical properties and reactivity of supported titanium NTs for bacterial inactivation and organic pollutant removal.

In this work, we report on the effect of anodization time on the morphology, optical, and photocatalytic properties of TiO2 nanotubes (NTs) allowing bacterial inactivation and two organic pollutant degradation under low-intensity solar-simulated light. Scanning electron microscopy (SEM) showed that the length of the TiO2 NTs increased from 2.8 to 25.8μm as anodization time was increased from 15 to 300min at 60V, respectively. The X-ray diffraction (XRD) patterns showed that all samples crystallize in the anatase phase after annealing at 400°C for 3h. Samples anodized for 30 and 60min exhibit low diffuse reflection at 400nm, which was attributed to the disorder-induced exciton scattering at the molecular level. The intensity of the photoluminescence (PL) spectra was found to increase as the length of the NTs increases up to a maximum anodization time of 300min, revealing the contribution of bulk excitonic states. A maximum photoelectric conversion efficiency of 0.55% was obtained at a potential of - 0.5V vs. Ag/AgCl for TiO2 NTs anodized for 60min. The optimized NTs (anodized for 60min) showed a photocatalytic bacterial inactivation of a magnitude of 6 log within 360min and a degradation of indole and methylene blue (MB) under low-intensity solar-simulated light (50 mW/cm2). The stability of the prepared catalyst was tested over several cycles.

Indole metabolism mechanisms in a new, efficient indole-degrading facultative anaerobe isolate Enterococcus hirae GDIAS-5

Indole is an inter-species and inter-kingdom signaling molecule widespread in the natural world. A large amount of indole in livestock wastes makes it difficult to be degraded, which causes serious malodor. Identifying efficient and eco-friendly ways to eliminate it is an urgent task for the sustainable development of husbandry. While bioconversion is a widely accepted means, the mechanism of indole microbial degradation is little understood, especially under anaerobic conditions. Herein, a new Enterococcus hirae isolate GDIAS-5, effectively degraded 100 mg/L indole within 28 h aerobically or 5 days anaerobically. Three intermediates (oxindole, isatin, and catechol) were identified in indole degradation, and catechol was further degraded by a meta-cleavage catabolic pathway. Two important processes for GDIAS-5 indole utilization were discovered. One is Fe(III) uptake and reduction, which may be a critical process that is coupled with indole oxidation, and the other is the entire pathway directly involved in indole oxidation and metabolism. Furthermore, monooxygenase ycnE responsible for indole oxidation via the indole-oxindole-isatin pathway was identified for the first time. Bioinformatic analyses showed that ycnE from E. hirae formed a phylogenetically separate branch from monooxygenases of other species. These findings provide new targets and strategies for synthetic biological reconstruction of indole-degrading bacteria.

Nitrogen-doped carbon dots as electron “bridge” in heterostructure of alpha-Fe2O3/NCDs/g-C3N4 for efficient degradation of indole using heterogeneous photo-Fenton

A special component, acting as “bridge” in composite photocatalyst, can remarkably improve the transfer and migration of charges by strengthening interfacial contact and constructing conductive channels. Nitrogen-doped carbon dots (NCDs) may be suitable for the bridge due to great conductivity, sufficient surface groups and more delocalized electrons. Here, we fabricated a composite of α-Fe2O3/NCDs/g-C3N4 for heterogeneous photo-Fenton degradation of indole and investigated the “bridge” roles of NCDs. Although the introduction of NCDs reduced surficial adsorption and light absorption abilities, the composite has a significant improvement in photocurrent density and EIS spectra, which were attributed to the bridge of NCDs between α-Fe2O3 and g-C3N4 through Fe-O-C and N-CN bonds. Besides, great conductivity of NCDs is another important factor for the transfer channels of charges. Finally, a Z-scheme mechanism was proposed for explanation of the transfer and migration of charges.

Investigation of indole biodegradation by Cupriavidus sp. strain IDO with emphases on downstream biotransformation and indigo production.

Indole, as a typical N-heterocyclic aromatic pollutant, poses risks to living things; however, indole-biotransformation mechanisms remain under-discussed, especially those related to its downstream biotransformation. Here, we systematically investigated the characteristics of indole degradation by strain Cupriavidus sp. IDO. We found that Cupriavidus sp. IDO could utilize 25 to 150 mg/L indole within 40 h and identified three intermediates (2-oxindole, indigo, and isatin). Additionally, integrated genomics and proteomics analysis of the indole biotransformation mechanism in strain IDO revealed 317 proteins showing significant changes (262 upregulated and 55 downregulated) in the presence of indole. Among these, three clusters containing indole oxidoreductase, CoA-thioester ligase, and gentisate 1,2-oxidoreductase were identified as potentially responsible for upstream and downstream indole metabolism. Moreover, HPLC-MS and -omics analysis offered insight into the indole-degradation pathway in strain IDO. Furthermore, the indole oxidoreductase IndAB, whichinitiates indole degradation, was heterologously expressedin Escherichia coli BL21(DE3). Optimization by the response surface methodology resulted in a maximal production of 135.0 mg/L indigo by the recombination strains in tryptophan medium. This work enriches our understanding of the indole-biodegradation process and provides new insights into multiple indole-degradation pathways in natural environments.

The performance and pathway of indole degradation by ionizing radiation

Indole is a typical recalcitrant aromatic nitrogen heterocyclic compound, which usually exists in coal chemical wastewater, and cannot be effectively removed by conventional wastewater treatment process. In this study, ionizing radiation was applied for the degradation of indole in aqueous solution. The effect of absorbed dose (1, 2, 3 and 5 kGy), initial concentration of indole (10, 20, 40 and 100 mg/L) and pH (3, 5, 7 and 9) on the degradation of indole was investigated. The results showed that the removal efficiency of indole was 99.2% at its initial concentration of 10 mg/L, absorbed dose of 2 kGy, and pH of 5. In addition, quenching experiments confirmed that three reactive species, including hydroxyl radical, hydrated electron and hydrogen radical, contributed to indole degradation. Five intermediate products were identified during indole degradation, including 3-methylindole, 3-methylinodle radicals, hydroxylation inodole, anilinoethanol and isatoic acid. The possible pathway of indole degradation was proposed. The acute toxicity and chronic toxicity of intermediate products of indole degradation were significantly reduced, except for 3-methylindole. In summary, ionizing radiation is alternative technology for the degradation of indole in coal chemical wastewater.

Cu(II)/Z4A as an Efficient Nanocomposite for Oxidative Degradation of Indole and Optimization of Effective Factors via RSM Procedure

One of the aromatic contaminants in the oil and fuel is indole, which is toxic even at low doses and is considered as air and water pollutant. In this research, the surface of Zeolite 4A (Z4A) was modified by Cu(II)nanoparticles to introduce a desirable nanocomposite (Cu(II)/Z4A) for indole oxidative degradation. Catalysts characterization was carried out by XRD, SEM, EDS, FTIR, and BET/BJH techniques. Response Surface Methodology (RSM) based on Box-Behnken Design (BBD) was employed for studying several effective factors influences in indole oxidation process, including pH, weight percentage of loaded copper (Cu(wt %)), mass of composite, and indole initial concentration (IND concentration). The obtained results by BBD revealed the solution pH was the most pivotal factor in indole oxidative degradation and predicted that under the optimum experimental conditions, the efficiency should be 98.91%. Moreover, GC-mass analysis was applied for evaluating side products, of which results led to some mechanisms and new productions to be found by using indole oxidative degradation. The results also demonstrated that due to indole oxidation and applying the proper solvent (ethanol), some side products were generated capable of acting as a fuel octane number enhancer, which may play a significant role in obtaining more valuable fuels.

Photochemical Degradation of an Environmental Pollutant by Pure ZnO and MgO Doped ZnO Nanocatalysts

MgO doped ZnO and pure ZnO nanoparticles were successfully synthesized by the sedimentary method. The products were characterized by XRD, TEM, and EDX. XRD patterns showed that the doped nanoparticles had the same crystal structures as the pure ZnO nanoparticles. Pure ZnO nanoparticles had a larger lattice volume than MgO doped ZnO nanoparticles. The photochemical degradation of indole 3- butyric acid as a pollutant in aqueous solutions was investigated by both pure and MgO doped ZnO under UV light irradiation. The effect of different parameters such as indole 3- butyric acid concentration, photocatalyst amount, PH, oxidant concentration on degradation of I-3BA, and optimum condition was obtained.

Enhanced anaerobic degradation of quinoline and indole with dried Chlorella pyrenoidosa powder as co-metabolic substance

In coal gasification wastewater (CGW), nitrogen heterocyclic compounds (NHCs) are important refractory compounds. However, NHCs negatively impact human health and the environment due to its toxic, carcinogenic, and mutagenic properties. The main objective of this study was to determine the feasibility of Chlorella pyrenoidosa as a co-metabolite in enhancing anaerobic degradation of NHCs in CGW. So far, there have been few studies on enhanced anaerobic degradation with Chlorella pyrenoidosa as a co-metabolic substance. It was speculated that Chlorella pyrenoidosa had certain feasibility in the enhanced degradation of NHCs. Anaerobic Reactor 1 was operated as a control, while Reactor 2 was operated with the addition of Chlorella pyrenoidosa. When the concentration of Chlorella pyrenoidosa was 100 μg/L, Reactor 2 showed optimum degradation ratios on quinoline (100%) and indole (100%). Variations in the concentrations of Chlorella pyrenoidosa did not benefit the degradation efficiency of the reactor, whereby low dosages were not conducive for the microorganism’s growth and high dosages resulted in a competitive inhibition between the Chlorella powder and refractory compounds. In the effluent of Reactor 1, quinoline and indole concentrations were 12.79 ± 1.21 and 18.45 ± 1.11 mg/L, respectively. In Reactor 2, neither quinoline nor indole were detected. Acute bio-toxicity tests indicated a decrease in toxicity with the addition of Chlorella powder, hence reducing the inhibitions on seed germination and root elongation. The addition of Chlorella powder resulted in the increase of tryptophan protein and polysaccharide content in the extracellular polymeric substance of anaerobic sludge. In Reactor 2, bacterial community structures became more diverse and richer. Archaea communities became richer, but diversity declined. In the enhanced anaerobic degradation of NHCs, Chlorella pyrenoidosa powder was found to be an effective co-metabolite.

A novel approach to efficient degradation of indole using co-immobilized horseradish peroxidase-syringaldehyde as biocatalyst

Biocatalytic degradation technology has received a great deal of attention in water treatment because of its advantages of high efficiency, environmental friendliness, and no secondary pollution. Herein, for the first time, horseradish peroxidase and mediator syringaldehyde were co-immobilized into functionalized calcium alginate composite beads grafted with glycidyl methacrylate and dopamine. The resultant biocatalyst of the co-immobilized horseradish peroxidase-syringaldehyde system has displayed excellent catalytic performance to degrade indole in water. The degradation rate of 100% was achieved in the presence of hydrogen peroxide even if the indole concentration was changing from 25 mg/L to 500 mg/L. If only the free enzyme was used under the identical water treatment conditions, the degradation of indole could hardly be observed even when the concentration of indole is low at 25 mg/L. This was attributed to the effective co-immobilization of the enzyme and the mediator so that the catalytic activity of horseradish peroxidase and the synergistic catalytic action of syringaldehyde could be fully developed. Furthermore, while the spherical catalyst was operated in succession and reused for four cycles in 50 mg/L indole solution, the degradation rate remained 91.8% due to its considerable reusability. This research demonstrated and provided a novel biocatalytic approach to degrade indole in water by the co-immobilized horseradish peroxidase-syringaldehyde system as biocatalyst.

Enhanced biodegradation of quinoline and indole with a novel symbiotic system of Polyurethane-chlorella-bacteria

Nitrogenous heterocyclic compounds in coal gasification wastewater have a great threat to human health and ecological environment. In recent years, algal-bacterial symbiotic system has been applied to industrial wastewater treatment. The aim of this work was to study an algal-bacteria symbiotic system of Polyurethane(PU)-chlorella-bacteria for strengthening degradation of nitrogen heterocyclic compounds. The results indicated PU-chlorella-bacteria system showed better stability and higher degradation ratio on quinoline and indole. Ammonia nitrogen (NH3-N) was released from the transformation of quinoline and indole in PU-chlorella-bacteria, and the presence of chlorella could decrease the NH3-N concentration. Illumination time of 12 h/24 h was more conducive to the degradation of refractory pollutants. Under the enhancement of PU-chlorella-bacteria, acute toxicity analysis demonstrated that the toxic inhibition on barley seeds decreased effectively. Enriched Chlorobaculum, Aquabacterium, Levilinea, and Longilinea may be responsible for the degradation of quinoline and indole.