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.     

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.     

Biosorption of uranium by Pseudomonas aeruginosa strain CSU: characterization and comparison studies

Pseudomonas aeruginosa strain CSU, a nongenetically engineered bacterial strain known to bind dissolved hexavalent uranium (as UO(2) (2+) and/or its cationic hydroxo complexes), was characterized with respect to its sorptive activity (equilibrium and dynamics). Living, heat-killed, permeabilized, and unreconstituted lyophilized cells were all capable of binding uranium. The uranium biosorption equilibrium could be described by the Langmuir isotherm. The rate of uranium adsorption increased following permeabilization of the outer and/or cytoplasmic membrane by organic solvents such as acetone. P. aeruginosa CSU biomass was significantly more sorptive toward uranium than certain novel, patented biosorbents derived from algal or fungal biomass sources. P. aeruginosa CSU biomass was also competitive with commercial cation-exchange resins, particularly in the presence of dissolved transition metals. Uranium binding by P. aeruginosa CSU was clearly pH dependent. Uranium loading capacity increased with increasing pH under acidic conditions, presumably as a function of uranium speciation and due to the H(+) competition at some binding sites. Nevertheless, preliminary evidence suggests that this microorganism is also capable of binding anionic hexavalent uranium complexes. Ferric iron was a strong inhibitor of uranium binding to P. aeruginosa CSU biomass, and the presence of uranium also decreased the Fe(3+) loading when the biomass was not saturated with Fe(3+), suggesting that Fe(3+) and uranium may share the same binding sites on biomass. Although the equilibrium loading capacity of uranium was greater than that of Fe(3+), this biomass showed preference of binding Fe(3+) over uranium. Thus, a two-stage process in which iron and uranium are removed in consecutive steps was proposed for efficient use of the biomass as a biosorbent in uranium removal from mine wastewater, especially acidic leachates. (c) 1996 John Wiley & Sons, Inc.     

Biosorption of uranium by cross-linked and alginate immobilized residual biomass from distillery spent wash

Residual biomass from a whiskey distillery was examined for its ability to function as a biosorbent for uranium. Biomass recovered and lyophilised exhibited a maximum biosorption capacity of 165–170?mg uranium/g dry weight biomass at 15?°C. With a view towards the development of continuous or semi-continuous flow biosorption processes it was decided to immobilize the material by (1) cross-linking with formaldehyde and (2) introducing that material into alginate matrices. Cross-linking the recovered biomass resulted in the formation of a biosorbent preparation with a maximum biosorption capacity of 185–190?mg/g dry weight biomass at 15?°C. Following immobilization of biomass in alginate matrices it was found that the total amount of uranium bound to the matrix did not change with increasing amounts of biomass immobilized. It was found however, that the proportion of uranium bound to the biomass within the alginate-biomass matrix increased with increasing biomass concentration. Further analysis of these preparations demonstrated that the alginate-biomass matrix had a maximum biosorption capacity of 220?mg uranium/g dry weight of the matrix, even at low concentrations of biomass.     

Studies on the biosorption of uranium by Talaromyces emersonii CBS 814.70 biomass

Residual biomass, produced by the thermophilic fungus, Talaromyces emersonii CBS 814.70, following growth on glucose-containing media, was examined for its ability to take up uranium from aqueous solution. It was found that the biomass had a relatively high observed biosorption capacity for the uranium (280 mg/g dry weight biomass). The calculated maximum biosorption capacity obtained by fitting the data to a Langmuir model was calculated to be 323 mg uranium/g dry weight biomass. Pretreatment of the biomass with either dilute HCl or NaOH brought about a significant decrease in biosorptive capacity for uranium. Studies on the effects of variation in temperature on the biosorptive capacity demonstrated no significant change in binding between 20°C and 60°C. However, a significant decrease in biosorptive capacity was observed at 5°C. Binding of uranium to the biomass at all temperatures reached equilibrium within 2 min. While the routine binding assays were performed at pH 5.0, adjustment of the pH to 3.0 gave rise to a significant decrease in biosorption capacity by the biomass. The biosorptive capacity of the biomass for uranium was increased when extraction from solution in sea-water was examined.     

The effect of pulse voltage and capacitance on biosorption of uranium by biomass derived from whiskey distillery spent wash

Biosorption of uranium by residual biomass from The Old Bushmill's Distillery Co. Ltd., Bushmills, Co. Antrim, Northern Ireland, following exposure to short and intense electric pulses has been examined. The biomass was prepared from the distillery spent wash and consisted of non-viable yeast and bacterial cells. As shown previously, untreated biomass had a maximum biosorption capacity of 170?mg uranium/g dry weight biomass. When biosorption reactions were placed between two electrodes and exposed to electric pulses with field strengths ranging from 1.25–3.25?kV/cm at a capacitance of 25?μF, biosorption increased from 170?mg of uranium to 275?mg uranium/g dry weight biomass. The data were obtained from biosorption isotherm analyses and taken as the degree of biosorption at residual uranium concentrations of 3?mM. In addition, when the capacitance of the electric pulses increased from 0.25?μF to 25?μF at a fixed pulse field strength the degree of biosorption increased from 210?mg uranium to 240?mg uranium/g dry weight biomass. The results suggest that application of short and intense electric pulses to biosorption reactions may play an important role in enhancing microbial biosorption of toxic metals/radionuclides from waste water streams.     

The effect of electric field stimulation on the biosorption of uranium by non-living biomass derived from Kluyveromyces marxianus IMB3

Summary Non-living biomass from the thermotolerant, ethanol-producing yeast strain Kluyveromyces marxianus IMB3 is capable of uranium biosorption. The biomass has an observed biosorption capacity of 115mg uranium/g dry weight of biomass with a calculated value of 127mg uranium/g dry weight. Following exposure of the biomass to electric fields of 2,500 V/cm for 20msec. the maximum biosorption capacity (observed or calculated) for uranium did not differ significantly for the untreated biomass. However, at lower residual concentrations of uranium (<10mg/L) the capacity of the treated biomass for uranium was significantly increased above values obtained with untreated material.     

Removal of uranium from solution using residual brewery yeast: combined biosorption and precipitation

Whilst unwashed preparations of biomass from a local brewery had an apparentmaximum biosorption capacity for uranium of 360mg/g (dry weight biomass) washingreduced this maximum to 150mg/g. Homogenization of both biomass preparations andrecovery of cellular debris had no significant effect on the maximum biosorptioncapacities although at lower equilibrium concentrations of uranium differences inthe biosorption capacities were detected. When unwashed biomass was retained by asemi-permeable membrane 40% of uranium used in the experiments precipitated outsidethat membrane. Therefore a significant proportion of the uranium removed fromsolution, and previously attributed to biosorption by the yeast biomass,resulted from precipitation brought about by interaction with low molecularweight components loosely associated with the biomass.     

The effect of pulse field strength on electric field stimulated biosorption of uranium by Kluyveromyces marxianus IMB3

Summary Improved biosorption of uranium by Kluyveromyces marxianus IMB3 biomass was achieved by increasing the electric field strength of delivered pulses from 1.25kV/cm to 2.5kV/cm. Although this had little or no effect on the maximum biosorption capacity (q_max), at low concentrations of uranium the amount bound to the biomass increased from 70 to 140mg uranium/g biomass. Significant increases in the maximum biosorption capacities (119–180 mg uranium/g biomass) were observed when the pulse field strength was increased from 2.5kV/cm to 3.25kV/cm.     

Characterization of acetone-washed yeast biomass functional groups involved in lead biosorption

The mechanism of lead cation biosorption by acetone-washed biomass of Saccharomyces uvarum was investigated by chemical modifications and spectroscopic monitoring of the cell components. Reacting the carboxyl groups with propylamine, which neutralizes these anions, considerably decreased the metallic ion uptake, indicating that negatively charged carboxyl groups play an important role in lead bisorption due to electrostatic attraction. After lead biosorption the photoacoustic Fourier transform infrared spectroscopy showed a change in the symmetrical stretch of the carboxylate groups of the acetone-washed yeast biomass, and the X-ray photoelectron spectroscopy oxygen peak was also found to be shifted. These findings support the hypothesis that lead uptake occurs mainly through binding to the carboxyl group. In X-ray photoelectron spectroscopy the nitrogen peak decreased after the biosorption of lead, suggesting that nitrogen-containing groups are also involved in the biosorption process. Acylation of amino groups was shown to increase the lead biosorption capacity. The acylation reaction converts the positively charged amino group to an amide capable of coordination to lead cations. Deproteination by boiling the biosorbent with NaOH increased the lead uptake. The acetone-washed biomass uptake of lead from an aqueous solution at ph 5.5 was 48.9 mg/g dry weight. Pure chitin adsorbed 48.8 mg lead/g dry weight. Mannan isolated from S. uvarum did not adsorb lead at all. Electrostatic attraction of the carboxyl groups and other anions present in the acetone-washed biomass, and complexation with nitrogen atoms, especially in chitin, appear to be the main mechanisms involved in lead cation biosorption. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 1-10, 1997.     

Studies on the biosorption of uranium by a thermotolerant, ethanol-producing strain of Kluyveromyces marxianus

The ability of residual biomass from the thermotolerant ethanol-producing yeast strain Kluyveromyces marxianus IMB3 to function as a biosorbent for uranium has been examined. It was found that the biomass had an observed maximum biosorption capacity of 120?mg U/g dry weight of biomass. The calculated value for the biosorption maximum, obtained by fitting the data to the Langmuir model was found to be 130?mg U/g dry weight biomass. Maximum biosorption capacities were examined at a number of temperatures and both the observed and calculated values obtained for those capacities increased with increasing temperature. Decreasing the pH of the biosorbate solution resulted in a decrease in uptake capacity. When biosorption reactions were carried out using sea-water as the diluent it was found that the maximum biosorption capacity of the biomass increased significantly. Using transmission electron microscopy, uranium crystals were shown to be concentrated on the outer surface of the cell wall, although uranium deposition was also observed in the interior of the cell.     

Biosorption of uranium by Myxococcus xanthus

This paper deals with uranium biosorption by Myxococcus xanthus biomass in which dry biomass, accumulating up to 2.4 mM of uranium g⁻¹, is demonstrated to be a more efficient biosorbent than wet biomass. For uranium concentrations of 0.1–0.3 mM, between 95.79% and 95.99% of the uranium was taken up from the solution. Dry biomass biosorption was found to be relatively rapid, reaching equilibrium after 5–10 min. In addition, the pH influenced biosorption, pH 4.5 promoting maximum uptake. It was also established that the biosorbed uranium is located on the cellular wall and within the extracellular mucopolysaccharide of this microorganism. Furthermore, using sodium carbonate as a desorbent agent, 80.82% of the biosorbed uranium could be recovered. The results obtained indicate the possible utilization of M. xanthus biomass to solve some problems of the water contaminated by uranium.     

Biosorption of uranium by lake-harvested biomass from a cyanobacterium bloom

The aim of this work was to study some basic aspects of uranium biosorption by powdered biomass of lake-harvested cyanobacterium water-bloom, which consisted predominantly of Microcystis aeruginosa. The optimum pH for uranium biosorption was between 4.0 and 8.0. The batch sorption reached the equilibrium within 1 h. The isotherm fitted the Freundlich model well. Although the Langmuir model fitted the experiment data well at pH 3.0, 5.0 and 7.0, it did not fit at pH 9.0 and 11.0 at all. This implies that different biosorption mechanisms may be involved at different pH values. 0.1 N HCl was effective in uranium desorption. The results indicated that the naturally abundant biomass of otherwise nuisance cyanobacterium bloom exhibited good potential for application in removal of uranium from aqueous solution.     

Cyanobacteria as a biosorbent for mercuric ion

The biosorption of Hg(2+) by two strains of cyanobacteria, Spirulina platensis and Aphanothece flocculosa, was studied under a batch stirred reaction system. Essential process parameters, including pH, biomass concentration, initial metal concentration, and presence of co-ions were shown to influence the Hg(2+) uptake. Hg(2+) uptake was optimal at pH 6.0 for both strains. The maximum loading capacities per gram of dry biomass were found to be 456 mg Hg(2+) for A. flocculosa and 428 mg Hg(2+) for S. platensis. At an initial concentration of 10 ppm Hg(2+), A. flocculosa was able to remove more than 98% of the mercury ion from solution. The biosorption kinetics of both strains showed that the metal uptake is bi-phasic, exhibiting a rapid initial uptake followed by a slower absorption process. The presence of dissolved Co(2+), Ni(2+), and Fe(3+) were found to play a synergistic role for Hg(2+) uptake by both strains. Regeneration of the biomass was examined by treating Hg(2+)-loaded samples with HCl and NH(4)Cl over four cycles of sorption and desorption.     

Biosorption of cadmium and lead ions by ethanol treated waste baker's yeast biomass

The biosorption of cadmium and lead ions from artificial aqueous solutions using waste baker's yeast biomass was investigated. The yeast cells were treated with caustic, ethanol and heat for increasing their biosorption capacity and the highest metal uptake values (15.63 and 17.49 mg g(-1) for Cd(2+) and Pb(2+), respectively) were obtained by ethanol treated yeast cells. The effect of initial metal concentration and pH on biosorption by ethanol treated yeast was studied. The Langmuir model and Freundlich equation were applied to the experimental data and the Langmuir model was found to be in better correlation with the experimental data. The maximum metal uptake values (qmax, mg g(-1)) were found as 31.75 and 60.24 for Cd(2+) and Pb(2+), respectively. Competitive biosorption experiments were performed with Cd(2+) and Pb(2+) together with Cu(2+) and the competitive biosorption capacities of the yeast biomass for all metal ions were found to be lower than in non-competitive conditions.     

Characterization of chitinases of polycentric anaerobic rumen fungi

Chitinolytic systems of anaerobic polycentric rumen fungi of genera Orpinomyces and Anaeromyces were investigated in three crude enzyme fractions - extracellular, cytosolic and cell-wall. Endochitinase was found as a dominant enzyme with highest activity in the cytosolic fraction. Endochitinases of both genera were stable at pH 4.5-7.0 with optimum at 6.5. The Orpinomyces endochitinase was stable up to 50 degrees C with an optimum for enzyme activity at 50 degrees C; similarly, Anaeromyces endochitinase was stable up to 40 degrees C with optimum at 40 degrees C. The most suitable substrate for both endochitinases was fungal cell-wall chitin. Enzyme activities were inhibited by Hg(2+) and Mn(2+), and activated by Mg(2+) and Fe(3+). Both endochitinases were inhibited by 10 mmol/L SDS and activated by iodoacetamide.     

Use of pelleted and immobilized yeast and fungal biomass for heavy metal and radionuclide recovery

Summary The biosorption of uranium, strontium and caesium by pelleted mycelium of two species of fungi,Rhizopus arrhizus andPenicillium chrysogenum and immobilizedSaccharomyces cerevisiae was evaluated in both batch and continuous flow systems where the presence of competing cations affected accumulation. The uptake mechanism for the pelleted fungal biomass differed from that of the immobilized yeast, the former being metabolism-independent biosorption of the metals while, in the presence of glucose, uptake in the latter organism was biphasic, surface biosorption being followed by energy-dependent influx. Removal of surface-bound metals was achieved by eluting with mineral acids or carbonate/bicarbonate solutions; a high degree of metal recovery was observed for uranium.     

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.     

Nikkomycin Z counteracts rylux BSU and Congo red inhibition ofSaccharomyces cerevisiae growth but does not prevent formation of aberrant cell walls

Rylux BSU and Congo red bind to chitin, interfere with proper cell-wall assembly, and stimulate chitin synthesis by increasing, most probably, chitin synthase 3 (ChS3) levels inSaccharomyces cerevisiae. On the other hand, the antibiotic nikkomycin Z inhibits chitin synthesis competitively. As ChS3 is the critical target of nikkomycin Z, its effect was tested in cells inhibited in growth by Rylux BSU or Congo red. Nikkomycin Z counteracted this inhibition but did not counteract aberrant cell-wall formation. These results indicate that chitin synthesis stimulation is the key step in Rylux BSU and Congo red inhibition and support the idea that increase in chitin synthesis represents a compensatory response to damaged cell-wall structure. As Rylux BSU and Congo red bind to newly synthesized chitin, further damage is caused in the wall and the response works in this case contrariwise. Nikkomycin Z breaks this vicious circle by counteracting the chitin synthesis stimulation.     

Characterization of Pb<Superscript>2+</Superscript> biosorption from aqueous solution by<Emphasis Type="Italic"> Rhodotorula glutinis</Emphasis>

The yeast Rhodotorula glutinis was examined for its ability to remove Pb(2+) from aqueous solution. Within 10 min of contact, Pb(2+) sorption reached nearly 80% of the total Pb(2+) sorption. The optimum initial pH value for removal of Pb(2+ )was 4.5-5.0. The percentage sorption increased steeply with the biomass concentration up to 2 g/l and thereafter remained more or less constant. Temperature in the range 15-45 degrees C did not show any significant difference in Pb(2+ )sorption by R. glutinis. The light metal ions such as Na(+), K(+), Ca(2+), and Mg(2+) did not significantly interfere with the binding. The Langmuir sorption model provided a good fit throughout the concentration range. The maximum Pb(2+ )sorption capacity q(max) and Langmuir constant b were 73.5 mg/g of biomass and 0.02 l/mg, respectively. The mechanism of Pb(2+) removal by R. glutinis involved biosorption by direct biosorptive interaction with the biomass through ion exchange and precipitation by phosphate released from the biomass.