Structural insights of a cellobiose dehydrogenase enzyme from the basidiomycetes fungus Termitomyces clypeatus

Filamentous fungi secrete various oxidative enzymes to degrade the glycosidic bonds of polysaccharides. Cellobiose dehydrogenase (CDH) (E.C.1.1.99.18) is one of the important lignocellulose degrading enzymes produced by various filamentous fungi. It contains two stereo specific ligand binding domains, cytochrome and dehydrogenase - one for heme and the other for flavin adenine dinucleotide (FAD) respectively. The enzyme is of commercial importance for its use in amperometric biosensor, biofuel production, lactose determination in food, bioremediation etc. Termitomyces clypeatus, an edible fungus belonging to the basidiomycetes group, is a good producer of CDH. In this paper we have analyzed the structural properties of this enzyme from T. clypeatus and identified a distinct carbohydrate binding module (CBM) which is not present in most fungi belonging to the basidiomycetes group. In addition, the dehydrogenase domain of T. clypeatus CDH exhibited the absence of cellulose binding residues which is in contrast to the dehydrogenase domains of CDH of other basidiomycetes. Sequence analysis of cytochrome domain showed that the important residues of this domain were conserved like in other fungal CDHs. Phylogenetic tree, constructed using basidiomycetes and ascomycetes CDH sequences, has shown that very surprisingly the CDH from T. clypeatus, which is classified as a basidiomycetes fungus, is clustered with the ascomycetes group. A homology model of this protein has been constructed using the CDH enzyme of ascomycetes fungus Myricoccum thermophilum as a template since it has been found to be the best match sequence with T. clypeatus CDH. We also have modelled the protein with its substrate, cellobiose, which has helped us to identify the substrate interacting residues (L354, P606, T629, R631, Y649, N732, H733 and N781) localized within its dehydrogenase domain. Our computational investigation revealed for the first time the presence of all three domains - cytochrome, dehydrogenase and CBM - in the CDH of T. clypeatus, a basidiomycetes fungus. In addition to discovering the unique structural attributes of this enzyme from T. clypeatus, our study also discusses the possible phylogenetic status of this fungus.     

Biosorption of chromium(VI) and arsenic(V) onto methylated yeast biomass

Yeast biomass was methylated in a 0.1 M HCl methyl alcohol solution at room temperature and the methylated yeast (MeYE) was applied to the adsorptive separation of Cr(VI) and As(V) anions from aqueous solutions. At near-neutral pH, while Cr(VI) and As(V) anions were scarcely adsorbed onto unmethylated yeast biomass, the amounts adsorbed increased with increasing methylation degree. The amount of Cr(VI) adsorbed onto MeYE was almost constant at pH 4-6 and decreased with increasing pH above pH 6. The amount of As(V) adsorbed onto MeYE was rather lower than that of Cr(VI) and it had a peak at about pH 7. A metal-binding model was used to describe the adsorption characteristics of Cr(VI) and As(V) on MeYE. The results showed that MeYE has two different types of adsorption sites. The saturated amount of Cr(VI) and As(V) adsorbed onto MeYE having methylation degree 0.94 was 0.55 mmol g(-1).     

海洋微藻富集微量元素研究进展

论述了微量元素对人体的重要作用,以及目前海洋微藻生物富集硒、铬、锌等的研究现状,同时探讨了微藻富集微量元素的前景。     

Biosorption of Cadmium by Phanerochaete Chrysosporium

The biosorption properties of cadmium(Ⅱ) by pre-treated biomass of Phanerochaete chrysosporium in the form of pellet were investigated. It was found that formaldehyde cross-linking and subsequent alkaline treatment could significantly improve the adsorption capacity of the biomass compared to other sorts of treatments, such as calcium chloride treatment, HCl treatment and,acetone treatment. Biosorption capacity of cadmium was examined as a function of physical and chemical factors including the pH of the metal solution pellet size, temperature and biomass concentration. The cadmium removal efficiency was strongly affected by pH. The maximal adsorption occurred around pH4.5. The pellet size also had a marked influence on the cadmium removal efficiency and the optimum size was the diameter range of 1.5-2.0 mm. The effect of biosorption temperature on cadmium uptake was inconspicuous between 25℃ and 35℃, but there was a notable decrease in cadmium uptake when the temperature reached 40℃. The cadmium removal efficiency increased as the biomass concentration when the initial cadmium ion concentration was 10 mg/L. When the biomass concentration was 2 g/L,the removal efficiency was 99.56%. However, the augment of the. removal efficiency was not obvious when the biomass concentration was more than 2 g/L. On the optimum conditions mentioned above,cadmium concentration could be reduced from 10 ppm down to 0.04 ppm that was below the Chinese National Waste Water Integrated Discharge Standard. In the biosotption process, most of the metal uptake happened during a short period immediately after the adsorption process started. It was observed that the biomass pellets had already adsorbed 83.36% of the total amount of cadmium finally adsorbed within the initial 10 minutes. The cadmium uptake rate decreased gradually afterwards. Sorption equilibrium could almost be established in 12 hours. This indicated that biosorption might consist of two processes:a fast surface binding process opcurring first and a slow membrane diffusion process taking place subsequently.     

Biosorption of radioactive thorium by Sargassum filipendula

In the present work, the biosorption of radioactive thorium was investigated using a dry biomass of Sargassum filipendula as the biosorbent material. Radioactive solutions containing between 2.0 and 500.0μg thorium were tested by biosorption with S. filipendula, yielding uptake capacities from 20 to 100%, depending on the concentration of the solution. Kinetic studies indicated that equilibrium between the thorium solution and the solid fraction was achieved after three hours of contact and that a second-order model could express the equilibrium kinetics. In order to investigate the maximum biosorption capacity of the biomass an isotherm was done, based on the experimental data, which revealed the maximum uptake capacity to be 2.59 μmol thorium/g biomass. The experimental data fitted well to a Langmuir model, which provided a good correlation between the experimental and predicted thorium uptake values.     

Biosorption of americium-241 by Saccharomyces cerevisiae

The biosorption of radionuclide ²⁴¹Am from solution by Saccharomyces cerevisiae (S. cerevisiae), and the effects of experimental conditions on the adsorption were investigated. The preliminary results showed thatS. cerevisiae is a very efficient biosorbent. An average of more than 99% of the total ²⁴¹Am could be removed by S. cerevisiae of 2.1 g/l (dry weight) from ²⁴¹Am solutions of 17.54–4386.0 mg/l (2.22 MBq/l–555 MBq/l) with adsorption capacities of 7.45–1880.0 mg/g biomass (dry weight) (0.94 MBq/g–237.9 MBq/g). The adsorption equilibrium was achieved within 1 hour and the optimum pH ranged 1–3. No significant differences on ²⁴¹Am adsorption were observed at 10–45 °C, or in solutions containing Au³⁺ or Ag⁺, even 2000 times above ²⁴¹Am concentration. The relationship between concentrations and adsorption capacities of ²⁴¹Am indicated the biosorption process should be described by the Freundlich adsorption isotherm.     

Biosorption of copper by biomass of extremophilic algae

Copper and lead are among the most important chemical pollutants of the environment including hydrosphere. Interaction of these heavy metals with biomass of aquatic plant organisms including algae is an area of active research in ecological chemistry. We investigated the interaction of the biomass of unique extremophilic (thermophilic) algae Galdieria sulphuraria with these heavy metals in aquatic environment using stripping voltammetry. Biosorption of copper by the studied biomass from aquatic medium has been discovered; however, no biosorption of another heavy metal from aquatic environment with the biomass has been detected. The experiments with the mortmass of Galdieria sulphuraria have revealed no sorption of the heavy metals as measured by stripping voltammetry. The difference in the interaction of copper and lead with the algal biomass is important for deeper understanding of the biosorption phenomenon. The new data stimulated further interest to the concept of biogenic migration of chemical elements that was proposed by V.I. Vernadskii. The results contributed to the scientific basis for innovative biotechnology to decontaminate water.     

Biosorption of 241Am by immobilized Saccharomyces cerevisiae

More than half of the world's annual production of radionuclides is used for medical purposes such as diagnostic imaging of diseases and patient therapy. Using aqueous homogeneous solution reactor technology, production quantities of medical radioisotopes ⁹⁹Mo and⁸⁹Sr, can be extracted from one reactor cycle. ⁹⁹Mo may be produced directly from UO₂SO₄ uranyl sulfate in an aqueous homogeneous solution nuclear reactor in a manner that produces high purity radionuclides, making efficient use of the reactor's uranium fuel solution. The process is relatively simple, economical, and waste free, eliminating uranium targets. The short-lived radioisotope ^99mTc is eluted from ⁹⁹Mo for diagnostic imaging. Radioisotope ⁸⁹Sr infusion is a therapeutic modality that reduces reliance on narcotic analgesia through palliation of metastatic bone pain caused by metastases of the cancer to the bone. Painful disseminated osseous metastases are common with carcinomas of the lung, prostate, and breast. Synergistic interleaving of two manufacturing processes, one producing ⁹⁹Mo and another producing ⁸⁹Sr in the same production cycle of an aqueous homogeneous solution reactor makes full and efficient use of the time for both the neutron irradiation stage and the extraction stage of each radionuclide. Interleaving the capture of ⁸⁹Sr radioisotope with production processing of ⁹⁹Mo radioisotope is achieved, since the extraction and subsequent elimination of radionuclide impurities occurs during separate parts of the reactor cycle. The process applies to either HEU or LEU nuclear fuels in an aqueous homogeneous solution reactor.     

Biosorption of Metal Ions by Spirulina plantensis Microalga

Russian Journal of General Chemistry - The sorption of lead, nickel, zinc, chromium(III), and chromium(VI) ions by Spirulina platensis microalga was studied. The effects of pH, metal concentration,...     

Biosorption of precious metal ions by chicken feather

Chicken feather (C-feather) is an intricate network of stable and water-insoluble protein fibers with high surface area and is an abundant bioresource. C-feather protein was found to accumulate various precious metal ions (gold and platinum metals) selectively from their dilute aqueous solutions in high yield and in short contact time, depending on pH and characteristics of the individual precious metal ions. Under certain condition, the sequestering level of precious ions, Au(III), Pt(II), and Pd(II) approaches about 17, 13, and 7% of dry wt of C-feather, respectively. Gold(III) potassium cyanade was also accumulated up to 5.5% at pH 2.0. The presence of 100-fold (mol) of coexisting cations, such as Na⁺, Fe(III), Cu(II), and Ni(II), did not show a discernible effect on the precious metal uptake rate and capacity of C-feather. Experiment suggested C-feather is promising for use in the removal/recovery of precious metals as well as water pollution control. A qualitative discussion is given about the excellent adsorption behavior of C-feather.

     

Biosorption of uranium by immobilized cells of Rhodotorula glutinis

Biosorption of uranium ions from diluted solution (≤40 mg L^?1) onto immobilized cells of Rhodotorula glutinis was investigated in a batch system. Equilibrium, kinetic and thermodynamic studies were conducted by considering the effect of initial uranium concentration, contact time and temperature. Non-linear forms of Langmuir, Freundlich and Sips isotherm models were used to fit the equilibrium data, Sips model was designated as the best one. Kinetic data were simulated by non-linear pseudo-first-order, pseudo-second-order and intra-particle diffusion equations. Pseudo-first-order kinetic equation described the experimental data better than pseudo-second-order equation and intra-particle diffusion equation can fit the kinetic data with two independent curves. Thermodynamic parameters, including ?H ⁰, ?G ⁰ and ?S ⁰, were evaluated, the sorption process was determined to be spontaneous and endothermic. Uranium sorption from pure uranium solutions and uranium pit wastewater by immobilized biomass and blank beads, as well as the regeneration results indicated that immobilized R. glutinis can be use to recovery uranium from uranium pit wastewater.     

Characterization and Biosorption Performance of Silver by Bacillus Licheniformis

The demand of silver is increasing rapidly in recent decades, because silver and its related products are widely used in modern industry and decoration. It is necessary to recover silver from waste water using an efficient and environmental friendly method due to its environmental and economic benefits. In this paper, we eliminated the interference of Cl-and light conditions, and then studied the characterization and biosorption performance of silver by Bacillus licheniformis. The max biosorption amount was 87.4 mg/g(dry weight) with the initial Ag+concentration of 100 mg/L at pH 6.0. XRD pattern showed that the product was an amorphous compound. SEM/EDS-mapping and FT-IR results implied that phosphate, amino and carboxyl groups located on the cell walls involved in the biosorption of Ag~+. The XPS spectra result showed that the value of EB of Ag 3d_(5/2_(367.51 eV) corresponded to the energy values for Ag(Ⅰ), and indicated Ag~+ adsorbed to the surface of cell still maintained mono-valence. The results confirm that B. licheniformis just adsorb Ag+ but cannot covert soluble Ag~+ to silver nano-particles(AgNP).     

Determination of chromium by atomic absorption spectrophotometry of chromium acetylacetonate : Determination of chromium in sea water

A sensitive atomic absorption method is described for the determination of chromium at sub-microgram levels. Chromium(III) is converted to its acetylacetone complex and extracted into MIBK. The atomic absorption sensitivity is thus en hanced two-fold compared to chromium (III) in aqueous medium. The detection limit of chromium is 0.015 p.p.m. with an acetylene-air flame; the sensitivity obtained with other chromium, methods under the same instrumental conditions is compared. The method can be applied to the determination of chromium in sea water; at a level of ca. 1.6 μg Cr/1, the precision is ±0.06 μg/1.     

Biosorption of heavy metal ions by immobilized zoogloea and zooglan

ImmobilizedZoogloea and zooglan in calcium alginate-silica matrix was shown to have a high adsorption capacity for Cu and Cd ions. Our results showed that Cu-ion uptake in the presence of Ca and Mg ions can be enhanced using immobilizedZoogloea and zooglan. Heavy metal ion adsorption efficiency decreased in the following order: Cu > Cd > Zn > Cr. The adsorbed metal ions were desorbed completely using sulfuric acid. ImmobilizedZoogloea and zooglan which was repetitively regenerated adsorbed heavy metal ions without a loss of adsorption capacity.     

Biosorption of nickel in complex aqueous waste streams by cyanobacteria

A study was undertaken to determined if a suitable biosorbent could be found for removal of nickel at low concentrations (< 20 parts per million [ppm]) from a chemically complex wastewater effluent generated by electroplating operations. Algae and cyanobacteria were chosen as candidate biosorbent materials because they are easy to grow and they have the ability to withstand processing into biosorbent materials. Several species were screened for nickel-biosorption capacity initially, and three species of cyanobacteria were selected for further study based on their performance in the scoping tests. When compared to live controls, autoclaving improved the binding capacities of all three species, but usually biosorption data from experiments with live cells were more consistent. None of the three species was able to bind nickel efficiently in actual effluent samples. Further experimentation indicated that sodium ions, which were present in high concentrations in the effluent, were interfering with the ability of the cells to bind nickel. Adsorption isotherm plots for biosorption of nickel by two species ofAnabaena in NiCl₂-deionized water solutions were prepared. Managed by Martin Marietta Energy Systems, Inc., for the US Department of Energy under contract No. DEAC05-84OR21400.     

Quantification of total chromium and hexavalent chromium in UHT milk by ETAAS

Procedures for the quantification of total chromium and hexavalent chromium in UHT milk samples are presented. Total chromium was determined directly in milk with the addition of a surfactant and a mixture of Pd and Mg as a chemical modifier. For the selective separation of hexavalent chromium, the sample pre-treatment consisted in precipitation of proteins and elution of the supernatant through a Chromabond NH2 column. The metal was eluted with nitric acid. Both total chromium and hexavalent chromium were evaluated by atomic absorption spectrometry with electrothermal atomization using the same instrumental conditions. The detection limits were 0.2 and 0.15 microgram l-1 for total chromium and hexavalent chromium, respectively. The linearity ranges under the optimized conditions were 0.2-20 and 0.15-50 micrograms l-1. For total chromium the precision was 4.9 and 5.7% for the analytical and the over-all procedure, respectively, and for hexavalent chromium 4.3 and 4.9%, respectively. The validation of both procedures was performed by the standard additions method and the recoveries were higher than 93% in all cases. For total chromium, a certified reference material was also used to validate the methodology. The methods were applied to the determination of total chromium and hexavalent chromium in 60 UHT milk samples.     

Biosorption of heavy metals by bacteria isolated from activated sludge

Twelve aerobic bacteria from activated sludge were isolated and identified. These included both Gram-positive (e.g., Bacillus) and Gram-negative (e.g., Pseudomonas) bacteria. The biosorption capacity of these strains for three different heavy metals (copper, nickel, and lead) was determined at pH 5.0 and initial metal concentration of 100 mg/L. Among these 12 isolates, Pseudomonas pseudoalcaligenes was selected for further investigation owing to its high metal biosorption capacity. The lead and copper biosorption of this strain followed the Langmuir isotherm model quite well with maximum biosorption capacity (q _max) reaching 271.7mg of Pb²⁺/g of dry cell and 46.8 mg of Cu²⁺/g of dry cell at pH 5.0. Study of the effect of pH on lead and copper removal indicated that the metal biosorption increased with increasing pH from 2.0 to 7.0. A mutual inhibitory effect was observed in the lead-copper system because the presence of either ion affected the sorption capacity of the other. Unequal inhibitions were observed in all the nickel binary systems. The increasing order of affinity of the three metals toward P. pseudoalcaligenes was Ni<Cu<Pb. The metal biosorptive potential of these isolates, especially P. pseudoalcaligenes, may have possible applications in the removal and recovery of metals from industrial effluents.     

Biosorption of Toxic Elements from Multicomponent Solutions by Microfungal Biomass

The results of experiments on sorption of toxic elements from multicomponent solutions by microfungal biomass are presented. In the elements group extraction processes the species and strain specificity of micromycetes manifests itself. Talaromyces funiculosus biomass possesses the highest (1.5–3 times higher) sorption indicators compared to Cladosporium cladosporioides and Trichoderma aureoviride. Within each species, the strains, isolated from technogenic substrates, are also characterized by higher sorption indicators. The affinity of chemical elements to fungal biomass as a sorbent corresponds to the following series: Bi ≈ Sn ≈ Pb ≈ Fe > Hg ≈ (Sb) ≥ Cr ≥ Cd > Cu ≈ Se > Zn ≈ V ≥ Co ≈ Mn ≈ As ≈ Ni ≈ Sr ≈ (Sb). The use of the analytical scanning electron microscopy has made it possible to detect particles of various composition and morphology on fungal biomass. The mechanism of their formation is proposed.     

Alginate Properties and Heavy Metal Biosorption by Marine Algae

The physical properties of the alginate component in four different brown seaweeds (Sargassumfluitans, Ascophyllum nodosum, Fucus vesiculo-sus, andLaminaria japonica) were characterized using potentiometric titration,¹³C-nuclear magnetic resonance (NMR), chemical analysis, and viscosity measurements. The heavy metal binding capacities of the corresponding seaweeds were directly proportional to their respective total carboxyl group content, and related to the electronegativity of the elements investigated (Ca, Zn, Cd, Cu, and Pb). The uronic acid composition or sequence of the alginate component did not affect the metal uptake properties of the biosorbents studied here. However, the alginate leaching owing to its solubilization by Na ions was observed to decrease with increasing intrinsic viscosity of the extracted alginate, related to its molecular weight, and with increasing apparent acidic dissociation constant, related to the alginate density inside the biomass.     

Determination of chromium by radiochemical displacement

A rapid and sensitive method has been developed for the determination of microgram amounts of chromium based on the radiochemical displacement of⁶⁵Zn from labeled Zn-[1-(2-pyridylazo-2-naphthol]₂ complex by chromium. The effect of pH on the displacement of⁶⁵Zn was studied. 5–65 g of chromium could be determined with great accuracy. The effect of various ions on the displacement of⁶⁵Zn by chromium was investigated and the method developed was utilized for the determination of chromium content present in geological water samples. The results were compared with values obtained by Atomic Absorption Spectrophotometry.