Physicochemical interaction of Escherichia coli cell envelopes and Bacillus subtilis cell walls with two clays and ability of the composite to immobilize heavy metals from solution.

Isolated Escherichia coli K-12 cell envelopes or Bacillus subtilis 168 cell walls were reacted with smectite or kaolinite clay in distilled deionized water (pH 6.0); unbound envelopes or walls were separated by sucrose density gradient centrifugation, and the extent of adsorption was calculated. At saturation, both clays adsorbed approximately 1.0 mg (dry weight) of envelopes or walls per mg (dry weight) of clay. Clays showed a preference for edge-on orientation with both walls and envelopes, which was indicative of an aluminum polynuclear bridging mechanism between the wall or envelope surface and the clay edge. The addition of heavy metals increased the incidence of planar surface orientations, which suggested that multivalent metal cation bridging was coming into play and was of increasing importance. The metal-binding capacity of isolated envelopes, walls, clays, and envelope-clay or wall-clay mixtures was determined by atomic absorption spectroscopy after exposure to aqueous 5.0 mM Ag+, Cu2+, Cd2+, Ni2+, Pb2+, Zn2+, and Cr3+ nitrate salt solutions at pHs determined by the buffering capacity of wall, envelope, clay, or composite system. The order of metal uptake was walls greater than envelopes greater than smectite clay greater than kaolinite clay for the individual components, and walls plus smectite greater than walls plus kaolinite greater than envelopes plus smectite greater than envelopes plus kaolinite for the mixtures. On a dry-weight basis, the envelope-clay and wall-clay mixtures bound 20 to 90% less metal than equal amounts of the individual components did.(ABSTRACT TRUNCATED AT 250 WORDS)     

Remobilization of toxic heavy metals adsorbed to bacterial wall-clay composites

Significant quantities of Ag(I), Cu(II), and Cr(III) were bound to isolated Bacillus subtilis 168 walls, Escherichia coli K-12 envelopes, kaolinite and smectite clays, and the corresponding organic material-clay aggregates (1:1, wt/wt). These sorbed metals were leached with HNO3, Ca(NO3)2, EDTA, fulvic acid, and lysozyme at several concentrations over 48 h at room temperature. The remobilization of the sorbed metals depended on the physical properties of the organic and clay surfaces and on the character and concentration of the leaching agents. In general, the order of remobilization of metals was Cr much less than Ag less than Cu. Cr was very stable in the wall, clay, and composite systems; pH 3.0, 500 microM EDTA, 120-ppm [mg liter-1] fulvic acid, and 160-ppm Ca remobilized less than 32% (wt/wt) of sorbed Cr. Ag (45 to 87%) and Cu (up to 100%) were readily removed by these agents. Although each leaching agent was effective at mobilizing certain metals, elevated Ca or acidic pH produced the greatest overall mobility. The organic chelators were less effective. Lysozyme digestion of Bacillus walls remobilized Cu from walls and Cu-wall-kaolinite composites, but Ag, Cr, and smectite partially inhibited enzyme activity, and the metals remained insoluble. The extent of metal remobilization was not always dependent on increasing concentrations of leaching agents; for example, Ag mobility decreased with some clays and some composites treated with high fulvic acid, EDTA, and lysozyme concentrations. Sometimes the organic material-clay composites reacted in a manner distinctly different from that of their individual counterparts; e.g., 25% less Cu was remobilized from wall- and envelope-smectite composites than from walls, envelopes, or smectite individually in 500 microM EDTA. Alternatively, treatment with 160-ppm Ca removed 1.5 to 10 times more Ag from envelope-kaolinite composites than from the individual components. The particle size of the deposited metal may account for some of the stability changes; those metals that formed large, compact aggregates (Cr and Ag) as seen by transmission electron microscopy were less likely to be remobilized. In summary, it is apparent that remobilization of toxic heavy metals in sediments, soils, and the vadose zone is a complicated issue. Predictions based on single inorganic or organic component systems are too simplistic.     

Remobilization of toxic heavy metals adsorbed to bacterial wall-clay composites.

Significant quantities of Ag(I), Cu(II), and Cr(III) were bound to isolated Bacillus subtilis 168 walls, Escherichia coli K-12 envelopes, kaolinite and smectite clays, and the corresponding organic material-clay aggregates (1:1, wt/wt). These sorbed metals were leached with HNO3, Ca(NO3)2, EDTA, fulvic acid, and lysozyme at several concentrations over 48 h at room temperature. The remobilization of the sorbed metals depended on the physical properties of the organic and clay surfaces and on the character and concentration of the leaching agents. In general, the order of remobilization of metals was Cr much less than Ag less than Cu. Cr was very stable in the wall, clay, and composite systems; pH 3.0, 500 microM EDTA, 120-ppm [mg liter-1] fulvic acid, and 160-ppm Ca remobilized less than 32% (wt/wt) of sorbed Cr. Ag (45 to 87%) and Cu (up to 100%) were readily removed by these agents. Although each leaching agent was effective at mobilizing certain metals, elevated Ca or acidic pH produced the greatest overall mobility. The organic chelators were less effective. Lysozyme digestion of Bacillus walls remobilized Cu from walls and Cu-wall-kaolinite composites, but Ag, Cr, and smectite partially inhibited enzyme activity, and the metals remained insoluble. The extent of metal remobilization was not always dependent on increasing concentrations of leaching agents; for example, Ag mobility decreased with some clays and some composites treated with high fulvic acid, EDTA, and lysozyme concentrations. Sometimes the organic material-clay composites reacted in a manner distinctly different from that of their individual counterparts; e.g., 25% less Cu was remobilized from wall- and envelope-smectite composites than from walls, envelopes, or smectite individually in 500 microM EDTA. Alternatively, treatment with 160-ppm Ca removed 1.5 to 10 times more Ag from envelope-kaolinite composites than from the individual components. The particle size of the deposited metal may account for some of the stability changes; those metals that formed large, compact aggregates (Cr and Ag) as seen by transmission electron microscopy were less likely to be remobilized. In summary, it is apparent that remobilization of toxic heavy metals in sediments, soils, and the vadose zone is a complicated issue. Predictions based on single inorganic or organic component systems are too simplistic.     

Adsorption of reovirus to clay minerals: effects of cation-exchange capacity, cation saturation, and surface area

The adsorption of reovirus to clay minerals has been reported by several investigators, but the mechanisms defining this association have been studied only minimally. The purpose of this investigation was to elucidate the mechanisms involved with this interaction. More reovirus type 3 was adsorbed, in both distilled and synthetic estuarine water, by low concentrations of montmorillonite than by comparable concentrations of kaolinite containing a mixed complement of cations on the exchange complex. Adsorption to the clays was essentially immediate and was correlated with the cation-exchange capacity of the clays, indicating that adsorption was primarily to negatively charged sites on the clays. Adsorption was greater with low concentrations of clays in estuarine water than in distilled water, as the higher ionic strength of the estuarine water reduced the electrokinetic potential of both clay and virus particles. The addition of cations (as chloride salts) to distilled water enhanced adsorption, with divalent cations being more effective than monovalent cations and 10(-2) M resulting in more adsorption than 10(-3) M. Potassium ions suppressed reovirus adsorption to montmorillonite, probably by collapsing the clay lattices and preventing the expression of the interlayer-derived cation-exchange capacity. More virus was adsorbed by montmorillonite made homoionic to various mono-, di-, and trivalent cations (except by montmorillonite homoionic to potassium) than by comparable concentrations of kaolinite homoionic to the same cations. The sequence of the amount of adsorption to homoionic montmorillonite was Al greater than Ca greater than Mg greater than Na greater than K; the sequence of adsorption to kaolinite was Na greater than Al greater than Ca greater than Mg greater than K. The constant partition-type adsorption isotherms obtained when the clay concentration was maintained constant and the virus concentration was varied indicated that a fixed proportion of the added virus population was adsorbed, regardless of the concentration of infectious particles. A heterogeneity within the reovirus population was indicated.     

Uptake and retention of metals by cell walls of Bacillus subtilis.

Isolated walls of Bacillus subtilis Marburg, prepared in a manner which avoided metal contamination other than by the growth medium, were incubated in dilute metal solutions, separated by membrane filtration (0.22 mum), and monitored by atomic absorption to give uptake data for 18 metals. Substantial amounts of Mg2+, Fe3+, Cu2+, Na+, and K+ (amounts which were often visible as Au3+, and Ni2+ (the higher atomic-numbered elements also visible as electron scattering), and small amounts of Hg2+, Sr2+, Pb2+, and Ag+ were taken into the wall. Some (Li+, Ba2+, Co2+, and Al3+) were not absorbed. Most metals which had atomic numbers greater than 11 and which could be detected by electron microscopy appeared to diffusely stain thin sections of the wall. Magnesium, on the other hand, partitioned into the central region, and these sections of walls resisted ruthenium red staining, which was not true for the other metals. Areas of the walls also acted as nucleation sites for the growth of microscopic elemental gold crystals when incubated in solutions of auric chloride. Retention or displacement of the metals was estimated by a "chromatographic" method using the walls cross-linked by the carbodiimide reaction to adipic hydrazide agarose beads (which did not take up metal but reduced the metal binding capacity of the walls by ca. 1%) packed in a column. When a series of 12 metal solutions was passed through the column, it became evident that Mg2+, Ca2+, Fe3+, and Ni2+ were strongly bound to the walls and could be detected by both atomic absorption and by their electron-scattering power in thin sections, qhereas the other metals were fisplaced or replaced. Partial lysozyme digestion of the walls (causing a 28% loss of a [3H]diaminopimelic acid label) greatly diminished the Mg2+ retention but not that of Ca2+, Fe3+, or Ni2+, indicating that there are select sites for various cations.     

Uptake of cobalt and cesium by microalgal- and cyanobacterial-clay mixtures

Accumulation of cobalt and cesium by the microalga Scenedesmus obliquus and the cyanobacterium Synechocystis PCC 6803 has been characterized at metal concentrations ranging from 1–100 µM in the presence of three clay minerals, montmorillonite, illite, and kaolinite. The majority of metal uptake over a 4 h period consisted of rapid binding to the clay mineral-cell aggregates, and was unaffected by incubation in the dark or by the presence of the metabolic inhibitor carbonyl cyanide-3-chlorophenyl hydrazone (CCCP). This was followed by a slower, energy-dependent uptake of metal by the cell components of the mixtures, which was inhibited by incubation in the dark or in the presence of CCCP. The initial phase of uptake by the clay mineral-cell mixtures and mixture components alone conformed to a Freundlich adsorption isotherm, the order of uptake for both cobalt and cesium being montmorillonite-cells > illite-cells > kaolinite-cells. S. obliquus-clay mineral mixtures accumulated more cobalt and cesium than Synechocystis PCC 6803-clay mineral mixtures. On a dry weight basis, clay minerals alone accumulated greater amounts of metals than clay mineral-cell mixtures, which accumulated more than the cells alone. However, when the same data was expressed as amount of metal adsorbed per unit surface area, S. obliquus, in most cases, adsorbed greater amounts of cobalt and cesium than the clay minerals or Synechocystis PCC 6803. As the proportion of clay in a cell-clay mineral mixture was increased, the amount of metal accumulated also increased. Reduced accumulation of cobalt and cesium by cell-clay mineral mixtures, exhibited by equal amounts of the individual components added together, indicated that the formation of clay-cell aggregates had masked some of the binding sites normally available to metal ions. Accumulation of cobalt and cesium by all clay mineral-cell mixtures was dependent on the external pH and NaCl concentration, and decreased with decreasing pH and increasing external NaCl concentration. Offprint requests to: G. M. Gadd.     

Adsorption of reovirus to clay minerals: effects of cation-exchange capacity, cation saturation, and surface area.

The adsorption of reovirus to clay minerals has been reported by several investigators, but the mechanisms defining this association have been studied only minimally. The purpose of this investigation was to elucidate the mechanisms involved with this interaction. More reovirus type 3 was adsorbed, in both distilled and synthetic estuarine water, by low concentrations of montmorillonite than by comparable concentrations of kaolinite containing a mixed complement of cations on the exchange complex. Adsorption to the clays was essentially immediate and was correlated with the cation-exchange capacity of the clays, indicating that adsorption was primarily to negatively charged sites on the clays. Adsorption was greater with low concentrations of clays in estuarine water than in distilled water, as the higher ionic strength of the estuarine water reduced the electrokinetic potential of both clay and virus particles. The addition of cations (as chloride salts) to distilled water enhanced adsorption, with divalent cations being more effective than monovalent cations and 10(-2) M resulting in more adsorption than 10(-3) M. Potassium ions suppressed reovirus adsorption to montmorillonite, probably by collapsing the clay lattices and preventing the expression of the interlayer-derived cation-exchange capacity. More virus was adsorbed by montmorillonite made homoionic to various mono-, di-, and trivalent cations (except by montmorillonite homoionic to potassium) than by comparable concentrations of kaolinite homoionic to the same cations. The sequence of the amount of adsorption to homoionic montmorillonite was Al greater than Ca greater than Mg greater than Na greater than K; the sequence of adsorption to kaolinite was Na greater than Al greater than Ca greater than Mg greater than K. The constant partition-type adsorption isotherms obtained when the clay concentration was maintained constant and the virus concentration was varied indicated that a fixed proportion of the added virus population was adsorbed, regardless of the concentration of infectious particles. A heterogeneity within the reovirus population was indicated.     

Reductions in the Toxicity of Cadmium to Microorganisms by Clay Minerals

The clay minerals montmorillonite and kaolinite protected bacteria, including actinomycetes, and filamentous fungi from the inhibitory effects of cadmium (Cd). Montmorillonite provided greater protection than did equivalent concentrations of kaolinite. The protective ability of the clays was correlated with their cation exchange capacity (CEC). The greater the CEC, the greater the absorbancy of exogenous Cd by the exchange complex and the greater the protection. The greater protection afforded by montmorillonite, as compared to kaolinite, was correlated with its higher CEC. Clays homoionic to Cd did not protect against exogenous Cd, as the exchange complex was already saturated with Cd. Montmorillonite homoionic to Cd was more detrimental to microbial growth than was kaolinite homoionic to Cd, as more Cd was present on and apparently desorbed from the montmorillonite.     

Mechanism of silicate binding to the bacterial cell wall in Bacillus subtilis.

To investigate the chemical mechanism of silicate binding to the surface of Bacillus subtilis, we chemically modified cell wall carboxylates to reverse their charge by the addition of an ethylenediamine ligand. For up to 9 weeks, mixtures of Si, Al-Fe-Si, and Al-Fe-Si plus toxic heavy metals were reacted with these cells for comparison with control cells and abiotic solutions. In general, more Si and less metal were bound to the chemically modified surfaces, thereby showing the importance of an electropositive charge in cell walls for fine-grain silicate mineral development. The predominant reaction for this development was the initial silicate-to-amine complexation in the peptidoglycan of ethylenediamine-modified and control cell walls, although metal ion bridging between electronegative sites and silicate had an additive effect. The binding of silicate to these bacterial surfaces can thus be described as outer sphere complex formation because it occurs through electrostatic interaction.     

Binding of metals to cell envelopes of Escherichia coli K-12.

As representative of gram-negative bacteria, the isolated and purified envelopes of an Escherichia coli K-12 strain were used to determine metal-binding capacity. The envelopes were suspended in 5 mM metal solutions for 10 min and 23 degrees C, separated and washed by centrifugation, and analyzed for metal by either atomic absorption or X-ray fluorescence spectroscopy. Of 32 metals tested, large amounts (> 0.9 mumol/mg [dry weight]) of Hf and Os, intermediate amounts (0.1 to 0.4 mumol/mg [dry weight]) of Pb, Zn, Zr, Fe III, Mn, Mo, Mg, Co, and Ce IV, and small amounts (< 0.1 mumol/mg [dry weight]) of Na, K, Rb, Ca, Sr, Cu, Sc, La, Pr, Sm, U, Fe II, Ru, Ni, Hg, Pt, Pd, Au, and In were detected Li and V were not bound to the envelopes. Electron microscopy of unstained, thin-sectioned material provided an electron-scattering profile for localizing the bound metal within the envelope. Energy-dispersive X-ray analysis of thin sections detected all metals in single envelope vesicles. These data suggest that most metal deposition occurred at the polar head group regions of the constituent membranes or along the peptidoglycan layer. No leaching of envelope components was detected by monitoring radioactive probes within the lipopolysaccharide and peptidoglycan layers during metal uptake experiments, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from metal-loaded envelopes, or protein and carbohydrate determinations on the wash fluids. These results suggest that membrane integrity was not disturbed under these ionic conditions.     

The membrane-induced proton motive force influences the metal binding ability of Bacillus subtilis cell walls.

Bacillus subtilis 168 is a gram-positive bacterium whose cell wall contains the highly electronegative polymers peptidoglycan (chemotype A1 gamma) and glycerol-based teichoic acid to produce a surface with a net negative charge with high metal binding capacity. During metabolism, a membrane-induced proton motive force continuously pumps protons into the wall fabric. As a result, a competition between protons and metal ions for anionic wall sites occurs, and less metal is bound in living cells than in nonliving cells or those in which the plasma membrane has been uncoupled. This was shown by using two metallic ions, UO2(2+) and Sc3+, on control cells, cells uncoupled with either carbonyl cyanide m-chlorophenylhydrazone or NaN3, or cells killed by gamma radiation. Transmission electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma atomic-emission spectroscopy showed that more metal was retained in the walls of nonliving cells and those with deenergized membranes than in their living counterparts.     

Prebiotic nucleotide oligomerization in a fluctuating environment: Effects of kaolinite and cyanamide

Summary The clay kaolinite was tested for its ability to promote nucleotide oligomerization in model prebiotic systems. Heterogeneous mixtures of clay, water and nucleotide were repeatedly evaporated to dryness at 60°C and redissolved in water in cyclic fashion in the presence or absence of cyanamide and/ or ammonium chloride. With or without cycling, kaolinite alone did not promote the oligomerization of nucleotides at detectable levels. Cycling of clay in combination with cyanamide, however, promoted high levels of condensation to a mixture of oligonucleotides and dinucleotide pyrophosphate without requiring ammonium chloride. Although cycling with clay favored synthesis of dinucleotide pyrophosphate, cycling without clay enhanced formation of oligonucleotides. These results support the hypothesis that the presence of clays in fluctuating environments would have influenced the course of prebiotic condensation reactions.     

Insecticidal Activity of the Toxins from Bacillus thuringiensis subspecies kurstaki and tenebrionis Adsorbed and Bound on Pure and Soil Clays

The release of transgenic plants and microorganisms expressing truncated genes from various subspecies of Bacillus thuringiensis that encode active insecticidal toxins rather than inactive protoxins could result in the accumulation of these active proteins in soil, especially when bound on clays and other soil particles. Toxins from B. thuringiensis subsp. kurstaki and B. thuringiensis subsp. tenebrionis, either free or adsorbed at equilibrium or bound on pure clay minerals (montmorillonite or kaolinite) or on the clay size fraction of soil, were toxic to larvae of the tobacco hornworm (Manduca sexta) and the Colorado potato beetle (Leptinotarsa decemlineata), respectively. The 50% lethal concentrations (LC(inf50)) of free toxins from B. thuringiensis subsp. kurstaki were higher than those of both bound and adsorbed complexes of these toxins with clays, indicating that adsorption and binding of these toxins on clays increase their toxicity in diet bioassays. The LC(inf50) of the toxin from B. thuringiensis subsp. tenebrionis that was either free or adsorbed on montmorillonite were comparable, whereas the toxin bound on this clay had higher LC(inf50) and the toxin bound on kaolinite had lower LC(inf50) than when adsorbed on this clay. Results obtained with the clay size fraction separated from unamended soil or soil amended with montmorillonite or kaolinite were similar to those obtained with the respective pure clay minerals. Therefore, insecticidal activity of these toxins is retained and sometimes enhanced by adsorption and binding on clays.     

Clay Mineralogy of Central Victorian (Creswick) Soils: Clay Mineral Contents as a Possible Tool of Environmental Indicator

The clay mineralogy and heavy metal/metalloid (As, Pb and Cu) contents of soils developed on the various rock units in a central highlands environment in Victoria (Creswick, Australia) have been investigated. The clay minerals identified showed an order of abundance as: kaolinite ? illite > smectite > mixed-layer (ML) ≈ vermiculite. The soil clay mineralogy did not change systematically with depth (0～ 10, 10～ 20 and 20～ 30 cm) and showed large variations spatially. The high proportion of kaolinite was probably due to the removal of 2:1 phyllosilicates by the formation of 1:1 kaolinite through weathering, which also reduced the cation exchange capacity (CEC) and electrical conductivity (EC, soil: water ratio of 1:5) of soils by aging. Soils were classified as silty loam to loam with a low clay size (≤ 2μ m) fraction. The soils were acidic to moderately acidic with pH ranging from 4.5 to 7.1, averaging 5.7. Concentrations of As, Pb, and Cu (average values 24.3, 16.7 and 11.0 mg/kg, respectively) did not show an association with the clay mineral contents except vermiculite. The occurrence of smectite and mixed-layer clay contents, although far lower than kaolinite and illite, contributed significantly to CEC of soils. The study area was affected by mining, high natural background As values dominate the area and the role of clay minerals in fixation of metalloid/metals was found to be less significant. Low organic matter content (average ～ 6.5%), low soil surface area (average ～ 1.0 m²/g) and the high proportion of kaolinite mineral content result in a limited ability to fix heavy metals. The role of Fe oxides appeared to be a key influence in the fixation of As and other potentially toxic metals, rather than the clay minerals, and therefore requires further research. This work highlighted the importance of the determination of types and amounts of clay minerals of natural soils in environmental management.     

Establishment of willow cuttings grown in porous membrane root envelopes

Small diameter fine, fibrous roots of willow are exceedingly difficult to remove from most soils. Where field retrieval of entire plants including clean roots may be important, porous membrane rooting envelopes are a method of choice.Purple osier willow (Salix purpurea L.) stem cuttings (clone SP3) were field rooted in buried porous membrane envelopes permeable to water and nutrients. Ramets were grown for two and four months, then separated into component parts for dry weight analysis.At two months, cuttings grown in rooting envelopes were no different in shoot dry weight than plants grown in clay pots or in soil. Tests indicated that rooting envelopes may be reused at least once without affecting shoot or total plant dry weight. Likewise, membrane pore sizes of 0.45, 1.2 and 3 m did not affect SP3 dry weight in four month tests. The importance of matching plant material and experiment duration to envelope size was illustrated by the limitation of growth by envelope edges at four months compared to two months.     

Transmission Electron Microscopic Observation of Mercury-Bearing Bacterial Clay Minerals in a Small-Scale Gold Mine in Tanzania

Mercury is a toxic substance that is widely distributed throughout the hydrosphere, biosphere, and lithosphere. Mine waste environments and mine waters support a wide diversity of microbial life. The microbial ecology of environments where mine waters are polluted with heavy metals is poorly understood. Here, we describe the features of bacteria in mercury-contaminated gold panning ponds in a small-scale gold mine (Geita) near Lake Victoria, Tanzania using energy filtering transmission electron microscopy (EF-TEM) and scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy (STEM-EDX). Most bacteria in the panning pond showed thick exopolysaccharides (EPSs), and many clay minerals attached onto the surface of EPSs. The clay minerals and EPSs might act as protective layers for the bacteria against toxic materials. The clay minerals were composed of smectite, halloysite, and kaolinite associated with calcite and goethite. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy indicated that the bulk soil samples contained abundant Si, Al, K, Ca, and Fe with heavy metals such as Au, Ti, and Ag. The results indicate that Hg pollution from panning ponds is caused by not only volatilization of Hg from Au-Hg amalgams, but Hg is also released into the air as dust mixed with dry fine clays, suggesting high long-term environmental risks. Mercury-resistant bacteria associated with clay minerals may have a significant effect on the weathering processes of the ore during long-term bioremediation. The clay mineral complexes on the surface of bacterial cell walls are a stimulator for Hg-resistant bacterial growth in mud ponds contaminated with the Au-Hg materials.     

Interaction of Pseudomonas putida CZ1 with clays and ability of the composite to immobilize copper and zinc from solution

The present study was conducted to determine the abilities of the living and nonliving Pseudomonas putida CZ1 cells, clays (goethite, kaolinite, smectite and manganite) and their composites to accumulate copper and zinc from a liquid medium, and elucidate the role of microbes on the mobility of heavy metals. Various mixtures of bacteria and clays were exposed to solutions of 0.025 mM or 0.5mM Cu(II) and Zn(II) in 0.01M KNO(3) to differentiate between so-called "high-affinity" sites and "low-affinity" sites. Clays associated in an edge-on orientation to the cells was observed by electron microscope (EM) examination of these metal-treated bacteria-clay aggregates. Adsorption experiments and desorption with 1.0M CH(3)COOK solution indicated that clays contain more high-affinity copper binding sites and less high-affinity zinc binding sites than that of bacteria, however, bacteria are involved in more low-affinity heavy-metal-binding sites. Carboxyl group activity is more important at weak-binding sites than at strong-binding sites. TEM-EDS analysis confirmed that most of Zn removed from solution was associated with P. putida CZ1 in the composites. These results suggest that bacteria play an important role in regulating the mobility of heavy metals in the soil environment.     

Chemical and enzymatic extraction of heavy metal binding polymers from isolated cell walls of Saccharomyces cerevisiae

Isolated cell walls of the yeast Saccharomyces cerevisiae were treated by either chemical (alkali and acid) or enzymatic (protease, mannanase or beta-glucuronidase) processes to yield partially purified products. These products were partially characterized by infrared analysis. They were subsequently reacted with heavy metal cation solutions and the quantity of metal accumulated by the cell wall material determined. The Cu(2+) ion (0.24, 0.36, 1.12, and 0.60 mumol/mg) was accumulated to a greater extent than either Co(2+) (0.13, 0.32, 0.43, and 0.32 mumol/mg) or Cd(2+) (0.17, 0.34, 0.39, and 0.32 mumol/mg) by yeast cell walls, glucan, mannan, and chitin, respectively The isolated components each accumulated greater quantities of the cations than the intact cell wall. Removal of the protein component of the yeast cell walls by Pronase caused a 29.5% decrease in metal accumulation by yeast cell walls per mass, indicating the protein is a heavy metal accumulating component. The data indicate that the outer mannan-protein layer of the yeast cell wall is more important than the inner glucan-chitin layer in heavy metal action accumulation. (c) 1994 John Wiley & Sons, Inc.     

Adhesion of the clay minerals montmorillonite, kaolinite, and attapulgite reduces respiration of Histoplasma capsulatum

The respiration of three phenotypes of Histoplasma capsulatum, the causal agent of histoplasmosis in humans, was markedly reduced by low concentrations of montmorillonite but was reduced less by even higher concentrations of kaolinite or attapulgite (palygorskite). The reduction in respiration followed a pattern that suggested saturation-type kinetics: an initial sharp reduction that occurred with low concentrations of clay (0.01 to 0.5% [wt/vol]), followed by a more gradual reduction with higher concentrations (1 to 8%). Increases in viscosity (which could impair the movement of O2) caused by the clays were not responsible for the reduction in respiration, and the clays did not interfere with the availability of nutrients. Scanning electron microscopy after extensive washing showed that the clay particles were tightly bound to the hyphae, suggesting that the clays reduced the rate of respiration of H. capsulatum by adhering to the mycelial surface and, thereby, interfered with the movement of nutrients, metabolites, and gases across the mycelial wall.     

Adhesion of the clay minerals montmorillonite, kaolinite, and attapulgite reduces respiration of Histoplasma capsulatum.

The respiration of three phenotypes of Histoplasma capsulatum, the causal agent of histoplasmosis in humans, was markedly reduced by low concentrations of montmorillonite but was reduced less by even higher concentrations of kaolinite or attapulgite (palygorskite). The reduction in respiration followed a pattern that suggested saturation-type kinetics: an initial sharp reduction that occurred with low concentrations of clay (0.01 to 0.5% [wt/vol]), followed by a more gradual reduction with higher concentrations (1 to 8%). Increases in viscosity (which could impair the movement of O2) caused by the clays were not responsible for the reduction in respiration, and the clays did not interfere with the availability of nutrients. Scanning electron microscopy after extensive washing showed that the clay particles were tightly bound to the hyphae, suggesting that the clays reduced the rate of respiration of H. capsulatum by adhering to the mycelial surface and, thereby, interfered with the movement of nutrients, metabolites, and gases across the mycelial wall.