The role of chitin in uranium adsorption by R. arrhizus

In order to further refine and support the uranium biosorption mechanism hypothesis proposed for Rhizopus arrhizus, uranium competitive equilibrium uptake isotherms by chitin were determined at two different solution pH levels and in the presence of different concentrations of competing ions, namely, Cu(2+), Zn(2+), and Fe(2+). The co-ion effect became more poronounced as the co-ion concentration in solution and pH increased. Obtained equilibrium data are in agreement with uranium biosorption data reported earlier. Infrared, mass, and electron paramagnetic resonance (EPR) spectra of chitin before and after uranium uptake in the presence of the competing ions Cu(2+), Zn(2+), and Fe(2+) were recorded. The combination of the spectral data and the information from equilibrium studies supported the hypothesis advanced earlier on the mechanism of uranium uptake by R.arrhizus. In addition, the data suggested the participation of a free radical in uranium coordination by the cell wall chitin. The mechanism of reduction of the uranium uptake capacity of the biomass in the presence of competing ions was also elucidated further.     

The mechanism of thorium biosorption by Rhizopus arrhizus

Inactive cells of Rhizopus arrhizus have been documented to exhibit a high thorium biosorptive uptake (170 mg/g) from aqueous solutions. The mechanism of thorium sequestering by this biomass type was investigated following the same method as for the uranium biosorption mechanism. The thorium sequestering mechanism appeared somewhat different from that of uranium. Experimental evidence is presented which indicates that, at optimum biosorption pH (4), thorium coordinates with the nitrogen of the chitin cell wall network and, in addition, more thorium is absorbed by the external section of the fungal cell wall. At pH 2 the overall thorium uptake is reduced. The kinetic study of thorium biosorption revealed a very rapid rate of uptake. Unlike uranium at optimum solution pH, Fe(2+) and Zn(2+) did not interfere significantly with the thorium biosorptive uptake capacity of R. arrhizus.     

Comparison of biosorption properties of different kinds of fungi for the removal of Gryfalan Black RL metal-complex dye

Three kinds of filamentous fungi (Rhizopus arrhizus, Trametes versicolor, Aspergillus niger) were tested for their ability to adsorb Gryfalan Black RL metal-complex dye as a function of pH, temperature and dye concentration. R. arrhizus and T. versicolor exhibited the maximum dye uptake at pH 2.0 and at 25 degrees C while A. niger performed the highest dye biosorption at pH 1.0 and at 35 degrees C. Sorption capacity of each biosorbent increased with increasing initial dye concentration. Among the three fungi, R. arrhizus was the most effective biosorbent showing a maximum dye uptake of 666.7 mg g(-1). The Langmuir model described the equilibrium data of each dye-fungus system accurately in the concentration and temperature ranges studied. Kinetic analysis indicated that both adsorption kinetics and internal diffusion played an important role on controlling the overall adsorption rate for each fungus. Thermodynamic analysis verified that A. niger biosorption was endothermic while the others were exothermic.     

Biosorption of uranium and thorium

Selected samples of waste microbial biomass originating from various industrial fermentation processes and biological treatment plants have been screened for biosorbent properties in conjunction with uranium and thorium in aqueous solutions. Biosorption isotherms have been used for the evaluation of biosorptive uptake capacity of the biomass which was also compared to an activated carbon and the ion exchange resin currently used in uranium production processes. Determined uranium and thorium biosorption isotherms were independent of the initial U or Th solution concentration. Solution pH affected the exhibited uptake. In general, lower biosorptive uptake was exhibited at pH 2 than at pH 4. No discernible difference in uptake was observed between pH 4 and pH 5 where the optimum pH for biosorption lies. The biomass of Rhizopus arrhizus at pH 4 exhibited the highest uranium and thorium biosorptive uptake capacity (g) in excess of 180 mg/g. At an equilibrium uranium concentration of 30 mg/liter, R. arrhizus removed approximately 2.5 and 3.3 times more uranium than the ion exchange resin and activated carbon, respectively. Under the same conditions, R. arrhizus removed 20 times more thorium than the ion exchange resin and 2.3 times more than the activated carbon. R. arrhizus also exhibited higher uptake and a generally more favorable isotherm for both uranium and thorium than all other biomass types examined.     

On the mechanism of uranium binding to cell wall of <Emphasis Type="Italic">Chara fragilis</Emphasis>

Biosorption of uranium from nuclear waste liquids and contaminated surface waters and soils has recently attracted special interest. However, the detailed mechanism of uranium uptake by plants is not well understood. The aim of this work is to investigate the role of cell wall components of the freshwater alga Chara fragilis in uranium sequestration from its solution. Three types of algae preparations: extract of cell wall polysaccharides, dried and live algae were subjected to uranium solutions of different concentration and pH. FTIR and X-ray diffraction were used to assess both potential binding sites and the form of the uranyl sequestered by algae. Sorption of uranium by live and dry algae shows remarkable differences both in terms of overall uptake and mechanisms involved. All experiments are consistent with the conclusion that coprecipitation of uranyl species with CaCO3 is the major binding mechanism in uranium sequestration by Chara fragilis, while the direct exchange of Ca2+ with UO22+ has a minor role. Live algae are twice as efficient in sequestering uranium from solution than dried ones due to the formation of different crystalline forms such as aragonite and rutherfordine forming in live algae in the presence of the uranyl species in solution. It therefore appears that metabolic processes such as photosynthesis, most likely through the regulation of pH, play a key role in the uranium uptake by plants. Further understanding of the complex mechanism of metabolic control of the uranium uptake by plants is needed before the planning of bioremediation of this element.     

Aluminum Uptake by Neuroblastoma Cells

Aluminum uptake studies in viable neuroblastoma cells were performed. Aluminum uptake was largely dependent on the pH of the suspension medium. At physiological pH values, cells were apparently unable to incorporate detectable amounts of aluminum in the absence of proper mediators. Aluminum uptake was enhanced as the pH decreased, attaining a plateau at about pH 6.0. In experiments with 2 x 10(6) cells/ml, pH 6.0, and 25 microM aluminum in the medium, aluminum incorporation reached saturation at 5 nmol of aluminum/mg of cellular protein, accounting for 60-70% of aluminum added. At pH 6.0, cells showed a large capacity for accumulating aluminum; about 70% of intracellular aluminum was associated with the postmitochondrial fraction. At neutral pH, application of apotransferrin seemed to facilitate aluminum translocation into cells via membrane receptors. Fatty acids were also capable of mediating aluminum uptake at neutral pH, probably by forming aluminum-fatty acid complexes. Low molecular weight aluminum chelators, e.g., citrate, inhibited aluminum uptake. Treatment of cells with energy metabolism blockers had virtually no influence on aluminum uptake, indicative of passive mechanisms. The results suggest that aluminum uptake occurs via different modes dependent on growth conditions, such as medium pH.     

Effects of selected physical and chemical parameters on uranium uptake by the bacterium Chryseomonas MGF-48

The effect of selected physical and chemical parameters, including media composition, uranium concentration, and metabolic inhibitors, on uranium uptake from aqueous solution by Chryseomonas sp. MGF-48, a bacterium isolated from electroplating effluent, was analysed. It was found that 198 mg/g (dry weight) of uranium was taken up from a 150 ppm (mg/l) solution of uranium when cells were maintained under starvation conditions. Uranium was released from the cells by addition of sodium carbonate. Uptake of uranium was reduced when cells were subjected to pretreatment with ultraviolet (u.v.) light (263.7 nm, 10 min) or heat (100 °C, 15 min), i.e., 99.8 and 57.5 mg/g, respectively. Addition of 2, 4-dinitrophenol (10 mM) or sodium azide (0.1%) resulted in decreased uptake (129 and 123 mg/g, respectively), whereas addition of glycerol-2-phosphate (G-2-P) resulted in deposition of uranium. Maximum uptake of uranium occurred at pH 6.5. Uranium uptake in the presence of selected carbohydrates decreased as follows: xylose > arabinose > mannose > maltose > glucose. When Chryseomonas sp. MGF-48 was exposed to 5, 50, or 100 mg/l uranium prior to uptake experiments, a decrease in uranium uptake was noted. Furthermore, immobilization of the bacterial cells in a calcium-alginate medium reduced the efficiency of uptake, yielding only 60% uranium uptake. It is concluded that uranium uptake and accumulation by this bacterium involves both metabolism-independent absorption and metabolism-dependent absorption, the former being considered to be more efficient.     

Water activity and substrate concentration effects on lipase activity

Catalytic activity of lipases (from Rhizopus arrhizus, Canadida rugosa, and Pseudomonas sp. was studied in organic media, mainly diisopropyl ether. The effect of water activity (a(w)) on V(max) showed that the enzyme activity in general increased with increasing amounts of water for the three enzymes. This was shown both for esterification and hydrolysis reactions catalyzed by R. arrhizus lipase. In the esterification reaction the K(m) for the acid substrate showed a slight increase with increasing water activities. On the other hand, the K(m) for the alcohol substrate increased 10-20-fold with increasing water activity. The relative changes in K(m) were shown to be independent of the enzyme studied and solvent used. The effect was attributed to the increasing competition of water as a nucleophile for the acyl-enzyme at higher water activities. In a hydrolysis reaction the K(m) for the ester was also shown to increase as the water activity increased. The effect of water in this case was due to the fact that increased concentration of one substrate (water), and thereby increased saturation of the enzyme, will increase the apparent K(m) of the substrate (ester) to be determined. This explained why the hydrolysis rate decreased with increasing water activity at a fixed, low ester concentration. The apparent V(max) for R. arrhizus lipase was similar in four of six different solvents that were tested; exceptions were toulene and trichloroethylene, which showed lower values. The apparent K(m) for the alcohol in the solvents correlated with the hydrophobicity of the solvent, hydrophobic solvents giving lower apparent K(m). (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 798-806, 1997.     

Environmental factors affecting the degradation of Dyfonate by soil fungi.

The ability of selected fungi to degrade the soil insecticide Dyfonate (O-ethyl S-phenyl ethylphosphonodithioate) into water-soluble, noninsecticidal metabolites was found to be dependent on the supply of nutrients, incubation time, temperature, pH, as well as other factors. With yeast extract as the carbon source (5 g/liter) and ammonium nitrate (1 g/liter) as the nitrogen source, both Rhizopus arrhizus and Penicillium notatum degraded the insecticide to a larger extent than with any other combination of nutrients used. With glucose as the carbon source, concentrations of ammonium nitrate above 5 g/liter inhibited the degradation of Dyfonate by R. arrhizus. Time-course studies on the metabolism of the insecticide indicated that Dyfonate was first absorbed by the fungal mycelium, where it was metabolized followed by the release of water-soluble, noninsecticidal, breakdown products into the culture media. The degradation appeared to involve the breakdown of Dyfonate into ethyl acetate soluble metabolites, such as ethylethoxyphosphonothioic acid, ethylethoxyphosphonic acid, methyl phenyl sulfoxide, and methyl phenyl sulfone. These compounds were then further degraded into water-soluble products. The optimum conditions for the degradation of the insecticide by R. arrhizus were observed at pH 6.0 to 7.0 and at 15-25 degrees C. Aged fungal mycelia were as active as mycelia in the logarithmic growth phase.     

Biosorption of uranium by magnetically modified Rhodotorula glutinis

Adsorption of uranium from aqueous solution onto the magnetically modified yeast cell, Rhodotorula glutinis, was investigated in a batch system. Factors influencing sorption such as initial solution pH, biomass dosage, contact time, temperature, initial uranium concentration and other common cations were analyzed. Sorption isotherm, kinetic and thermodynamic studies of uranium on magnetically modified R. glutinis were also carried out. The temperature dependent equilibrium data agreed well with the Langmuir model. Kinetic data obtained at different temperatures were simulated using pseudo-first-order and pseudo-second-order kinetic models, the pseudo-second-order kinetic model was found to describe the data better with correlation coefficients near 1.0. The thermodynamic parameters, ΔH°, ΔS° and ΔG° were calculated from the sorption data gained at different temperatures. These thermodynamic parameters showed that the sorption process was endothermic and spontaneous. All results indicated that magnetically modified R. glutinis can be a potential sorbent for uranium wastewater treatment.     

Characteristics of Aluminum Biosorption by Sargassum fluitans Biomass

Biomass of nonliving brown seaweed Sargassum fluitans pretreated by different methods is capable of taking up more than 10% (11 mEq/g) of its dry weight in aluminum at pH 4.5. There are indications that the biomass hydroxyl groups were involved in sequestering the aluminum in the form of polynuclear aluminum species. Aluminum-alginate complex (like cotton candy) was formed in the aluminum sorption solution as alginate was partially released from the biomass. Aluminum uptake of S. fluitans biomass was independent of residual alginate content in the biomass. Sodium ion added for pH adjustment was not adsorbed at all in the presence of aluminum ion. Received March 11, 1998; accepted October 9, 1998.     

The sub-cellular localisation and regulatory properties of pyruvate carboxylase from Rhizopus arrhizus

Cell-free extracts of Rhizopus arrhizus contain exclusively cytosolic pyruvate carboxylase and NAD-glutamate dehydrogenase, a single mitochondrial isoenzyme of NADP-isocitrate dehydrogenase, and both mitochondrial and cytosolic isoenzymes of NADP-malate dehydrogenase (decarboxylating). Other enzymes examined have sub-cellular localisations similar to those characteristic of mammalian liver. Purified preparations of R. arrhizus pyruvate carboxylase are subject to partial regulatory inhibition by L-aspartate and 2-oxoadipate. L-Glutamate acts as a less effective analogue of L-aspartate while 2-oxoglutarate is ineffective. Competition studies indicate the presence of separate inhibitory sites for L-aspartate and 2-oxoadipate. Under routine assay conditions R. arrhizus pyruvate carboxylase shows significant activation by acyl derivatives of coenzyme A with long chain acyl CoA being more effective than acetyl-CoA. This activation is no longer observed in the presence of high concentrations of pyruvate, MgATP2- and HCO-3. The concentrations of L-aspartate and 2-oxoadipate required to give 50% inhibition ([I]0.5), and the maximal extents of inhibition, are increased by addition of acetyl-CoA. Acetyl-CoA increases the sigmoidal character of the relationship: initial rate/[L-aspartate], but decreases this parameter for the relationship: initial rate/[2-oxoadipate]. The studies indicate that R. arrhizus possesses an entirely cytosolic pathway for the conversion of glucose to fumaric acid and that both the organisation of pyruvate metabolism and the regulation of pyruvate carboxylase differ significantly in this organism as compared to that proposed previously for Aspergillus nidulans.     

Improvement of heavy metal biosorption by mycelial dead biomasses (Rhizopus arrhizus, Mucor miehei and Penicillium chrysogenum): pH control and cationic activation

Abstract: Fungal mycelial by-products from fermentation industries present a considerable affinity for soluble metal ions (e.g. Zn, Cd, Ni, Pb, Cr, Ag) and could be used in biosorption processes for purification of contaminated effluents. In this work the influence of pH on sorption parameters is characterized by measuring the isotherms of five heavy metals (Ni, Zn, Cd, Ag and Pb) with Rhizopus arrhizus biomass under pH-controlled conditions. The maximum sorption capacity for lead was observed at pH 7.0 (200 mg g^-l), while silver uptake was weakly affected. The stability of metal-biosorbent complexes is regularly enhanced by pH neutralization, except for lead. A transition in sorption mechanism was observed above pH 6.0. In addition, comparison of various industrial fungal biomasses ( R. arrhizus, Mucor miehei and Penicillium chrysogenum indicated important variations in zinc-binding and buffering properties (0.24, 0.08 and 0.05 mmol g^−l, respectively). Without control, the equilibrium pH (5.8, 3.9 and 4.0) is shown to be related to the initial calcium content of the biosorbent, pH neutralization during metal adsorption increases zinc sorption in all fungi (0.57, 0.52 and 0.33 mmol g-l) but an improvement was also obtained (0.34, 0.33 and 0.10 mmol g⁻¹) by calcium saturation of the biomass before heavy metal accumulation. Breakthrough curves of fixed bed biosorbent columns demonstrated the capacity of the biosorbent process to purify zinc and lead solutions in continuous-flow systems, and confirmed the necessity for cationic activation of the biosorbent before contact with the heavy-metal solution.     

Influence of anions on metal adsorption by Rhizopus arrhizus biomass

The presence of anions in solution was found to inhibit the uptake of La(3+), Cd(2+), Pb(2+), UO(2+) (2), and Ag(+) by Rhizopus arrhizus biomass. The effects ranged from total inhibition of Cd(2+) and Pb(2+) uptake at equimolar concentrations of EDTA to no change in uptake of La(3+) or UO(2+) (2) at 12-fold molar excesses of Cl(-) or CO(2-) (3). No anion was found to enhance metal uptake levels, and the degree of inhibition generally followed the series: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm EDTA } \ge \ge {\rm SO}_{;{;{;{\rm 4} } } };{{\rm 2} - } \ge {\rm Cl}; - \ge {\rm PO}_{;{;{;{\rm 4} } } };{{\rm 3} - } \ge {\rm glutamate} \ge {\rm CO}_{;{;{\rm 3} } };{{\rm 2} - } $$\end{document} The chemical equilibrium model REDEQL2 was adapted to treat metal uptake by R. arrhizus biomass and used to predict the effects of anions in solution. Comparisons with the experimental results are made and discussed in light of the assumptions underlying the model.     

Cadmium triggers Elodea canadensis to change the surrounding water pH and thereby Cd uptake

This study was aimed to investigate the influence of Elodea canadensis shoots on surrounding water pH in the presence of cadmium and the effect of plant-induced pH on cadmium uptake. The pH change in the surrounding nutrient solution and Cd uptake by Elodea shoots were investigated after cultivation of various plant densities (1, 3, 6 plants per 500 ml) in hydroponics at a starting pH of 4.0 and in the presence of different concentrations of cadmium (0, 0.1, 0.5 microM). Cadmium uptake was also investigated at different constant pH (4.0, 4.5, 5.5 and 6.5). To investigate if the pH change arose from photosynthetic activities, plants were grown under light, darkness or in the presence of a photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and 0.5 microM cadmium in the solution. Elodea had an ability to increase the surrounding water pH, when the initial pH was low, which resulted in increased accumulation of Cd. The higher the plant density, the more pronounced was the pH change. The pH increase was not due to the photosynthetic activity since the pH rise was more pronounced under darkness and in the presence of DCMU. The pH increase by Elodea was triggered by cadmium.     

Uranium accumulation by Pseudomonas sp. EPS-5028

Summary Pseudomonas sp. EPS-5028 was examined for the ability to accumulate uranium from solutions. The uptake of uranium by this microorganism is very rapid and is affected by pH but not by temperature, metabolic inhibitors, culture time and the presence of various cations and anions. The amount of uranium absorbed by the cells increased as the uranium concentration of the solution increased up to 55 mg uranium/g cell dry weight. Electron microscopy indicated that uranium accumulated intracellularly as needle-like fibrils. Uranium could be removed chemically from the cells, which could then be reused as a biosorbent. Offprint requests to: A. M. Marqués     

Introduction

Biosorption of aluminum by sulfate-reducing bacteria isolated from uranium mine tailings was examined. A top agar method with Alizarin Red S was used for initial screening of the isolates for aluminum tolerance and biosorption. Five strains of aluminumion-fixing sulfate-reducing bacteria and a strain designated UFZ B 406 isolated from another source were used in the experiments. The mechanism of aluminum biosorption was found to be a passive one. Freezing and thawing of the cells resulted in higher sorption of aluminum, whereas heat treatment or the uncoupler carbonyl-cyanide-m- chlorophenylhydrazone (CCCP) had no effect. The pH value had significant influence on the aluminum ion adsorption, the most absorbance being at pH 3 and 5, and the lowest at pH 7. Addition of magnesium and the presence of iron sulfide precipitates decreased aluminum sorption. The relationship between biomass and Al3+ ions accumulated was linear. Polyphosphate granules as possible site of aluminum accumulation were not found to be present. Fluorescence microscopy showed deposition of aluminum ions exclusively on the surface of the cell. Use of the isolates in bioremediation processes for removing aluminum from water is considered.     

Selective recovery of uranium and thorium ions from dilute aqueous solutions by animal biopolymers

Selective actinide ion recovery from dilute, aqueous, multication waste streams is an important problem. The recovery of uranium (U) and thorium (Th) by various animal biopolymers was examined. Of four species of biopolymers tested, a high uptake of uranium and thorium was found in hen eggshell membrane (ESM) and silk proteins, with the maximum uranium and thorium recovery exceeding 98% and 79%, respectively. The uptake of U and Th was significantly affected by the pH of the solution. The optimum pH values were 6 and 3 for the uptake of U and Th, respectively. The effect of temperature differed with the metal. The uptake of U decreased with increasing temperature (30–50°C), whereas the Th uptake increased with increasing temperature. Selective recovery of U and Th from dilute aqueous binary and multimetal solutions was also examined. ESM and silk proteins tested were effective and selective for removing each metal by controlling the pH and temperature of the solution. In multimetal systems, the order of sorption of ESM proteins was preferential: U > Cu > Cd > Mn > Pb > Th > Ni > Co > Zn at pH 6 and Th > U > Cu > Pb > Cd > Mn > Co > Ni = Zn at pH 3. These biopolymers appear to have potential for use in a commercial process for actinide recovery from actinide-containing wastewater.     

Utilization of the coconut shell of babaçu (Orbignya sp.) to produce cement-bonded particleboard

The zinc biosorptive capacity of the brown seaweed Sargassum sp. (Phaeophyceae) was studied in the presence or absence of competing calcium ions, using a continuous system with tubular fixed-bed reactors. In order to detect the effect of calcium on zinc biosorption, a 130 mg/l zinc solution was used, and calcium was added at 50-340 mg/l. The potential zinc biosorptive capacity of the biomass was markedly influenced by the presence of ionic calcium. Zinc sorption decreased with increasing calcium concentrations, as expressed by zinc uptake rates. Calcium was effectively recovered only during the initial stages of the process, as expressed by the decrease in its uptake rates. Calcium uptake rates were also much higher than zinc uptake rates, indicating that calcium was preferentially recovered when compared to zinc.