Evaluation of p-cresol degradation with polyphenol oxidase (PPO) immobilized in various matrices

Tailoring polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads by controlling crosslinking pH and time

Hydrogel-encapsulated catalysts are an attractive tool for low-cost intensification of (bio)-processes. Polyvinyl alcohol-sodium alginate hydrogels crosslinked with boric acid and post-cured with sulfate (PVA-SA-BS) have been applied in bioproduction and water treatment processes, but the low pH required for crosslinking may negatively affect biocatalyst functionality. Here, we investigate how crosslinking pH (3, 4, and 5) and time (1, 2, and 8 h) affect the physicochemical, elastic, and process properties of PVA-SA-BS beads. Overall, bead properties were most affected by crosslinking pH. Beads produced at pH 3 and 4 were smaller and contained larger internal cavities, while optical coherence tomography suggested polymer cross-linking density was higher. Optical coherence elastography revealed PVA-SA-BS beads produced at pH 3 and 4 were stiffer than pH 5 beads. Dextran Blue release showed that pH 3-produced beads enabled higher diffusion rates and were more porous. Last, over a 28-day incubation, pH 3 and 4 beads lost more microspheres (as cell proxies) than beads produced at pH 5, while the latter released more polymer material. Overall, this study provides a path forward to tailor PVA-SA-BS hydrogel bead properties towards a broad range of applications, such as chemical, enzymatic, and microbially catalyzed (bio)-processes.

A systematic review on potential microbial carbohydrases: current and future perspectives

Various studies have shown that the microbial proteins are often more stable than belongs to other sources like plant and animal origin. Hence, the interest in microbial enzymes has gained much attention due to many potential applications like bioenergy, biofuel production, biobleaching, bioconversion and so on. Additionally, recent trends revealed that the interest in isolating novel microbes from harsh environments have been the main focus of many scientists for various applications. Basically, industrially important enzymes can be categorized into mainly three groups: carbohydrases, proteases, and lipases. Among those, the enzymes especially carbohydrases involved in production of sugars. Carbohydrases include amylases, xylanases, pectinases, cellulases, chitinases, mannases, laccases, ligninases, lactase, glucanase, and glucose oxidase. Thus, here, an approach has been made to highlight five enzymes namely amylase, cellulase, laccase, pectinase, and xylanase from different sources with special emphasis on their properties, mechanism, applications, production optimization, purification, molecular approaches for its enhanced and stable production, and also biotechnological perspectives of its future development. Also, green and sustainable catalytic conversion strategies using nanoparticles of these enzymes have also been discussed. This review will provide insight into the carbohydrases importance and their usefulness that will help to the researchers working in this field.

Density Functional Theory Calculations of the Effect of Oxygenated Functionals on Activated Carbon towards Cresol Adsorption

The mechanism of adsorption of p-cresol over activated carbon adsorbent and the specific role of oxygen functional groups on cresol adsorption were studied using density functional theory (DFT) calculations. All the energy calculations and geometry optimization pertaining to DFT calculations were done using the B3LYP hybrid functional at basis set 6-31g level of theory in a dielectric medium of ε = 80 (corresponding to water). The interaction of cresol with different activated carbon models, namely pristine activated carbon, hydroxyl functionalized activated carbon, carbonyl functionalized activated carbon, and carboxyl functionalized activated carbon, were considered, and their adsorption energies corresponded to −416.47 kJ/mol, −54.73 kJ/mol, −49.99 kJ/mol, and −63.62 kJ/mol, respectively. The high adsorption energies suggested the chemisorptive nature of the cresol-activated carbon adsorption process. Among the oxygen functional groups, the carboxyl group tended to influence the adsorption process more than the hydroxyl and carbonyl groups, attributing to the formation of two types of hydrogen bonds between the carboxyl activated carbon and the cresol simultaneously. The outcomes of this study may provide valuable insights for future directions to design activated carbon with improved performance towards cresol adsorption.

Intensified phenol and p-cresol biodegradation for wastewater treatment in countercurrent packed-bed column bioreactors

An intensified biodegradation process in packed-bed column bioreactors (PBCB) with microbial cells attached to packing/micro-particles surface was proposed and simulated via a dynamic 3D model with continuity, momentum, and species (comprising biomicro-particles) balance equations in liquid/gas, accumulation of biomicro-particles in packed-bed, diffusion and enzymatic reaction within biofilm and liquid film. Phenol and phenol/p-cresol biological removal by Pseudomonas putida was chosen to discuss the enhanced biodegradation efficiency. The biodegradation in single/dual-substrate systems is significantly upgraded as biomass loading on micro-particles surface increases. Microbial cells addition to the surface of micro-particles is more efficient when the foremost extent of biomass is attached to packing via large biofilms with increased resistance to mass transfer, at low phenol concentrations and liquid velocities. These intensified biodegradation systems aim at maximizing the mass transfer in PBCB for treatment of wastewater having high phenols concentration, without reducing the residence time of liquid or diluting the effluent.

Bio-based and cost effective method for phenolic compounds removal using cross-linked enzyme aggregates

This work aimed at presenting a green method using a new source of peroxidase isolated from Raphanus sativus var. niger (RSVNP) in immobilized form, for the treatment of wastewater. To ensure stability and enzymatic activity in the biodegradation process, RSVNP was immobilized as a cross-linked enzyme aggregate (CLEAs). With more than 29% of recovered activity and 85% aggregation yield, acetone was selected as the best precipitating agent. The formed protein aggregates required 2% (v/v) of glutaraldehyde (GA) concentration and a ratio of 9:1 (v/v) enzyme (E) amount to cross-linker (E/GA). Compared to the free enzyme, RSVNP-CLEAs were found more chemically and thermally stable and exhibited good storage stability for more than 8 weeks. In addition, RSVNP-CLEAs were evaluated for their ability to remove phenol and p-cresol from aqueous solution by varying several operating conditions. A maximal yield (98%) of p-cresol conversion was recorded after 40 min; while 92% of phenol was degraded after 1 h duration time. The reusability of RSVNP-CLEAs was tested, displaying 71% degradation of phenol in the third batch carried out and more than 54% was achieved for p-cresol after four successive reuses in the presence of hydrogen peroxide at 2 mM concentration.

Impact of immobilization technology in industrial and pharmaceutical applications

The current demands of the world's biotechnological industries are enhancement in enzyme productivity and development of novel techniques for increasing their shelf life. Compared to free enzymes in solution, immobilized enzymes are more robust and more resistant to environmental changes. More importantly, the heterogeneity of the immobilized enzyme systems allows an easy recovery of both enzymes and products, multiple reuse of enzymes, continuous operation of enzymatic processes, rapid termination of reactions, and greater variety of bioreactor designs. This review summarizes immobilization definition, different immobilization methods, advantages and disadvantages of each method. In addition, it covers some food industries, protein purification, human nutrition, biodiesel production, and textile industry. In these industries, the use of enzymes has become an inevitable processing strategy when a perfect end product is desired. It also can be used in many other important industries including health care and pharmaceuticals applications. One of the best uses of enzymes in the modern life is their application in diagnose and treatment of many disease especially when used in drug delivery system or when used in nanoform.

The multifunctional globin dehaloperoxidase strikes again: Simultaneous peroxidase and peroxygenase mechanisms in the oxidation of EPA pollutants

The multifunctional catalytic hemoglobin dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata was found to catalyze the H₂O₂-dependent oxidation of EPA Priority Pollutants (4-Me-o-cresol, 4-Cl-m-cresol and pentachlorophenol) and EPA Toxic Substances Control Act compounds (o-, m-, p-cresol and 4-Cl-o-cresol). Biochemical assays (HPLC/LC-MS) indicated formation of multiple oxidation products, including the corresponding catechol, 2-methylbenzoquinone (2-MeBq), and oligomers with varying degrees of oxidation and/or dehalogenation. Using 4-Br-o-cresol as a representative substrate, labeling studies with ¹⁸O confirmed that the O-atom incorporated into the catechol was derived exclusively from H₂O₂, whereas the O-atom incorporated into 2-MeBq was from H₂O, consistent with this single substrate being oxidized by both peroxygenase and peroxidase mechanisms, respectively. Stopped-flow UV-visible spectroscopic studies strongly implicate a role for Compound I in the peroxygenase mechanism leading to catechol formation, and for Compounds I and ES in the peroxidase mechanism that yields the 2-MeBq product. The X-ray crystal structures of DHP bound with 4-F-o-cresol (1.42 Å; PDB 6ONG), 4-Cl-o-cresol (1.50 Å; PDB 6ONK), 4-Br-o-cresol (1.70 Å; PDB 6ONX), 4-NO₂-o-cresol (1.80 Å; PDB 6ONZ), o-cresol (1.60 Å; PDB 6OO1), p-cresol (2.10 Å; PDB 6OO6), 4-Me-o-cresol (1.35 Å; PDB 6ONR) and pentachlorophenol (1.80 Å; PDB 6OO8) revealed substrate binding sites in the distal pocket in close proximity to the heme cofactor, consistent with both oxidation mechanisms. The findings establish cresols as a new class of substrate for DHP, demonstrate that multiple oxidation mechanisms may exist for a given substrate, and provide further evidence that different substituents can serve as functional switches between the different activities performed by dehaloperoxidase. More broadly, the results demonstrate the complexities of marine pollution where both microbial and non-microbial systems may play significant roles in the biotransformations of EPA-classified pollutants, and further reinforces that heterocyclic compounds of anthropogenic origin should be considered as environmental stressors of infaunal organisms.

Reactions of phenolic compounds with monomeric N-halamines and mesoporous material-supported N-halamines

The reactions of a monomeric N-halamine, 1-chloro-5,5-dimethylhydantoin (MCDMH), and a mesoporous material-supported N-halamine (MMSNs) with phenol and p-cresol (two common contaminants in water) were investigated. MCDMH reacted rapidly with the phenolic compounds, and pH values had little effects on the reactions. On the contrary, MMSNs reacted with phenol and p-cresol only when the pH values were higher than 10. Phenol showed a lower reaction rate than p-cresol toward MMSNs. GCMS analysis suggested that MMSNs might react with the phenolic compounds through step-wise electrophilic chlorination reactions, and the main product was 2,4,6-trichlorophenol. The reaction kinetics were studied by following the disappearance of phenolic UV absorption bands, and the kinetic parameters were determined.

Versatile Fungal Polyphenol Oxidase with Chlorophenol Bioremediation Potential: Characterization and Protein Engineering

Polyphenol oxidases (PPOs) have been mostly associated with the undesirable postharvest browning in fruits and vegetables and have implications in human melanogenesis. Nonetheless, they are considered useful biocatalysts in the food, pharmaceutical, and cosmetic industries. The aim of the present work was to characterize a novel PPO and explore its potential as a bioremediation agent. A gene encoding an extracellular tyrosinase-like enzyme was amplified from the genome of Thermothelomyces thermophila and expressed in Pichia pastoris The recombinant enzyme (TtPPO) was purified and biochemically characterized. Its production reached 40 mg/liter, and it appeared to be a glycosylated and N-terminally processed protein. TtPPO showed broad substrate specificity, as it could oxidize 28/30 compounds tested, including polyphenols, substituted phenols, catechols, and methoxyphenols. Its optimum temperature was 65°C, with a half-life of 18.3 h at 50°C, while its optimum pH was 7.5. The homology model of TtPPO was constructed, and site-directed mutagenesis was performed in order to increase its activity on mono- and dichlorophenols (di-CPs). The G292N/Y296V variant of TtPPO 5.3-fold increased activity on 3,5-dichlorophenol (3,5-diCP) compared to the wild type.IMPORTANCE A novel fungal PPO was heterologously expressed and biochemically characterized. Construction of single and double mutants led to the generation of variants with altered specificity against CPs. Through this work, knowledge is gained regarding the effect of mutations on the substrate specificity of PPOs. This work also demonstrates that more potent biocatalysts for the bioremediation of harmful CPs can be developed by applying site-directed mutagenesis.

Analytical study of effective biodegradation of p-cresol using Serratia marcescens ABHI001: application in bioremediation

This study evaluated the capability of Serratia marcescens ABHI001 to effectively degrade p-cresol through different techniques. The molecular identity of the laboratory isolate S. marcescens ABHI001 was confirmed through the 16S ribosomal DNA gene pattern, and its morphological features were investigated through field-emission scanning electron microscopy. In addition, the degradation behavior of the isolate for cresol was verified using several techniques, including UV-visible spectroscopy, followed by high-performance liquid chromatography (HPLC), gas chromatography, and Fourier transform infrared spectroscopy. The maximum degradation percentage of 85% for p-cresol could be achieved after 18 h of incubation with S. marcescens ABHI001. The formation of p-hydroxybenzaldehyde, p-hydroxybenzoate, and protocatechuate metabolites was confirmed through HPLC. The study results indicate that S. marcescens ABHI001 may have applications in the bioremediation of organic pollutants, such as p-cresol.

Purification and immobilization of laccase from Trichoderma harzianum strain HZN10 and its application in dye decolorization

In this study we report the purification of laccase produced by Trichoderma harzianum strain HZN10 (using wheat bran under solid state fermentation) and its application in decolorization of synthetic dyes. Extracellular laccase was purified to homogeneity by DEAE-Sepharose and Sephadex G-100 chromatography with specific activity of 162.5 U/mg and 25-fold purification. Purified laccase was immobilized in various entrapments like calcium alginate, copper alginate, calcium alginate–chitosan beads and sol–gel matrix. Optimization results revealed that the laccase immobilized in sol–gel was optimally active in wide pH range (4.0–7.0) and thermo-stable (50–70 °C) than free enzyme which was optimum at 50 °C and pH 6.0. Kinetic analysis showed K_m of 0.5 mM and 2.0 mM and V_max of 285 U/mg and 500 U/mg by free laccase and sol–gel immobilized laccase respectively with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) [ABTS] substrate. Free and immobilized laccase was employed for decolorization of three different synthetic dyes (malachite green, methylene blue and congo red). High performance liquid chromatography (HPLC) analysis results revealed that approximately 100% of malachite green, 90% of methylene blue and 60% of congo red dyes at initial concentration of 200 mg/L were decolorized within 16, 18 and 20 h, respectively by laccase immobilized in sol–gel matrix in the presence of 1-hydroxybenzotriazole (HBT) mediator. During the decolorization all three synthetic dyes showed various peaks on HPLC chromatogram indicating different by-products formation. Finally, phytotoxicity analysis results revealed that the by-products of synthetic dyes (formed during decolorization) showed less toxicity against Phaseolus mungo compared to untreated synthetic dyes.