Biodegradation of methyl parathion in the presence of goethite: The effect of Pseudomonas sp. Z1 adhesion

In this research, the influence of goethite on biodegradation kinetic of methyl parathion was investigated in the presence of Pseudomonas sp. Z1. Semipermeable membrane experiments were performed to demonstrate the role of adhesion of degrading bacteria to surface of goethite in biodegradation of methyl parathion. Sorption of methyl parathion and bacteria onto goethite particles were also measured to assess the distribution of methyl parathion and bacteria between water and goethite surface. The first-order degradation rate constant of methyl parathion in different concentrations of goethite was in the order of 0.1 g L⁻¹ > 0.01 g L⁻¹ > 0 g L⁻¹ > 1 g L⁻¹ > 20 g L⁻¹, suggesting the presence of low concentrations of goethite accelerated the biodegradation of methyl parathion and high concentrations of goethite inhibited this biodegradation process. According to the result of semipermeable membrane experiment, when no bacterial attachment occurred in the system, the promotive effect of 0.1 g L⁻¹ goethite for microbial degradation was disappeared and the inhibition effect of 20 g L⁻¹ goethite increased. The results clearly demonstrated that the adhesion of bacteria to goethite was beneficial to the biodegradation of methyl parathion. The information obtained is of fundamental significance for the understanding of microbial degradation of organic pollution in soil.     

Interfacial interaction between methyl parathion-degrading bacteria and minerals is important in biodegradation

In the present study, the influence of kaolinite and goethite on microbial degradation of methyl parathion was investigated. We observed that the biodegradation process was improved by kaolinite and depressed by goethite. Calorimetric data further showed that the metabolic activities of degrading cells (Pseudomonas putida) were enhanced by the presence of kaolinite and depressed by the presence of goethite. A semipermeable membrane experiment was performed and results supported the above observations: the promotive effect of kaolinite and the inhibition of goethite for microbial degradation was not found when the bacteria was enclosed by semipermeable membrane and had no direct contact with these minerals, suggesting the important function of the contact of cellular surfaces with mineral particles. The relative larger particles of kaolinite were loosely attached to the bacteria. This attachment made the cells easy to use the sorbed substrate and then stimulated biodegradation. For goethite, small particles were tightly bound to bacterial cells and limited the acquisition of substrate and nutrients, thereby inhibiting biodegradation. These results indicated that interfacial interaction between bacterial cells and minerals significantly affected the biodegradation of pesticides.     

Molecular structure of the outer bacterial membrane of Pseudomonas aeruginosa via classical simulation

A detailed structural analysis has been performed of the outer bacterial membrane of Pseudomonas aeruginosa using a parameterized classical simulation model (R. D. Lins and T. P. Straatsma, Biophysical Journal, 2001, Vol. 81, pp. 1037-1046) with modest modifications. The structural analysis of the membrane is presented and newly discovered characteristics of the membrane are discussed. Simulations indicate that the relative contribution of different ligands to calcium ion coordination varies across the membrane, while maintaining a constant average coordination number of 6.1. Water penetrates the surface of the membrane to a depth of about 30 A. The hydration of ions and phosphate groups is shown to depend on location within the membrane. A measure of saccharide residue orientation is defined and average orientations are presented. Saccharide residues possess varying degrees of motion with a trend of greater mobility at the membrane surface. However, their motion is limited and even in the membrane outer core region the average structure appears fairly rigid over a period of 1 ns.     

Oxidatively Damaged Erythrocytes Are Recognized by Membrane Proteins of Macrophages

Human erythrocytes incubated with an iron catalyst ADP-chelated Fe³⁺ undergo oxidative damage of the membrane including lipid peroxidation, protein oxidation, and protein aggregation, and become susceptible to recognition by human macrophages. In order to clarify the membrane components of macrophages responsible for the recogrution of the oxidized erythrocytes, binding of the oxidized cells to dot and Western blots of solubilized membrane of macrophages was investigated. The oxidized erythrocytes but not unoxidized cells bound to the dot blots. The binding was effectively inhibited by saccharide chains of band 3, a major glycoprotein of human erythrocytes, and lowered when the saccharide chains of band 3 were removed from the cell surface by pretreatment of the cells with endo-P-galactosidase which specifically cleaves the polylactosaminyl saccharide chains of band 3. The oxidized erythrocytes bound to the membrane proteins of macrophages with molecular mass of about 50, 80, and 120 kDa on Western blots depending on the saccharide chains of band 3 on their surface. The results suggest that the oxidatively damaged erythrocytes are specifically recognized by these proteins of macrophage membrane having saccharide binding ability.     

A stepwise approach to the understanding of extracellular enzyme activity in soil. I. Effect of electrostatic interactions on the conformation of a beta-D-glucosidase adsorbed on different mineral surfaces

The enzymatic activity of sweet almond beta-D-glucosidase adsorbed on various mineral surfaces was studied. Our aim was to elucidate the mechanism responsible for the observed changes in catalytic activity. The results of the investigation are discussed with reference to the hypotheses generally proposed to explain the well-documented shift in optimal pH of the activity of adsorbed enzymes. By separate determinations of enzymatic activity in a mineral suspension and of its supernatant solution, and comparison with a control without mineral added, we obtained accurate measurements of the catalytic activity of the adsorbed enzyme alone. Different pH profiles of activity profiles were found when the enzyme was adsorbed onto montmorillonite, kaolinite and goethite. The activity profiles, were also found to vary with ionic strength, the pH at which enzyme adsorbed onto the mineral surface, and in the case of goethite, on the nature of the anions in the buffer. Our observations cannot be adequately explained by assuming a more acidic microenvironment at the mineral surface. We postulate that on some mineral surfaces a conformational change is induced in the adsorbed protein, which reduces its catalytic activity. We contend that such conformational changes are due primarily to electrostatic forces.     

The distribution of Concanavalin A receptor sites on the membrane of chromaffin granules.

The distribution of concanavalin A (con A) receptor sites on the membranes of chromaffin granules has been investigated by binding studies using 125I-labelled con A and by electron-microscope studies using ferritin-labelled con A. In both experiments con A was observed to bind to chromaffin granule membranes but not to intact granules. The ferritin-con A particles bind to only one of the two possible surfaces of the chromaffin granule membranes. These results are in agreement with previous observations concerning the asymmetric distribution of saccharide residues on the surfaces of a number of different plasma membranes. They suggest that for the intracellular membrane of the chromaffin granule the saccharide sites, like those in plasma membranes, are not exposed to the cell cytoplasm. Further work is necessary to establish whether these sites are on the inner surface of the membrane or whether they are unmasked during the conversion of granules to membrane ghosts.     

The binding and reactions of nucleotides and polynucleotides on iron oxide hydroxide polymorphs

The iron oxide hydroxide minerals goethite and akaganéite were likely constituents of the sediments present in, for instance, geothermal regions of the primitive earth. They may have adsorbed organics and catalyzed the condensation processes which led to the origins of life. The binding to and reactions of nucleotides and oligonucleotides with these minerals was investigated. The adsorption of adenosine, 5-AMP, 3-AMP, 5-UMP, and 5-CMP to these minerals was studied. Adenosine did not bind to goethite and akaganéite. The adsorption isotherms for the binding of the nucleotides revealed that they all had close to the same affinity for the mineral. Binding to goethite was about four times stronger than to akagan éite. There was little difference in the adsorption of each nucleotide suggesting the binding was between the negative charge on the phosphate group and the positive charges on the mineral surface. The absence of binding of adenosine is consistent with this explanation. Binding decreases as the pH increases due to the titration of the positive (acidic) centers on the minerals. Two times as many moles of polynucleotides were bound to these minerals as compared to the mononucleotides. Watson-Crick hydrogen bonding of adenosine and 5-AMP to poly(U) complexes with goethite and akaganéite was observed. There was no interaction of uridine with the poly(U)-goethite complex as expected if Watson-Crick hydrogen bonding is taking place. Neither goethite nor akaganéite catalyzed the oligomerization of the phosphorimidazolide of adenosine (ImpA). The template directed synthesis of oligomers of 5-GMP on the poly(C) bound to goethite was observed. Higher molecular weight oligomers were observed when the poly (C) was bound to goethite than was found in the absence of the mineral.     

The three-dimensional structure of the 4:1 mithramycin:d(ACCCGGGT)(2) complex: evidence for an interaction between the E saccharides

Mithramycin and chromomycin, two antitumor drugs, each having an identical aglycone and nearly identical disaccharide and trisaccharide side chains, have differing binding properties to a small oligonucleotide, d(ACCCGGGT)(2) (M. A. Keniry et al., Journal of Molecular Biology, 1993, Vol. 231, pp. 753-767). In order to understand the forces that induce four mithramycin molecules to bind to d(ACCCGGGT)(2) instead of two drug molecules in the case of chromomycin, the structure of the 4:2:1 mithramycin: Mg(2+):d(ACCCGGGT)(2) complex was investigated by (1)H-nmr and restrained molecular dynamics. The resulting three-dimensional model showed that in order to accommodate the close approach of one neighboring mithramycin dimer, the inwardly directed CDE saccharide chain of the neighboring mithramycin dimer undergoes a conformational change such that the E saccharide no longer spans the minor groove but reorients so that the hydrophilic face of the E saccharides from the two dimers oppose each other. Two hydrogen bonds are formed between the hydroxyl groups of the two opposing E saccharide groups. The results are interpreted in terms of the differences in stereochemistry and functional group substitutions between mithramycin and chromomycin. A mithramycin dimer is able to self-associate on an oligonucleotide template because it has two hydroxyl groups on the same face of its terminal E saccharide. A chromomycin dimer is unable to self-associate because one of these hydroxyl groups is acetylated and the neighboring hydroxyl group has a stereochemistry that cannot permit close contact of the hydroxyl group with a neighbouring chromomycin dimer.Copyright 2000 John Wiley & Sons, Inc.     

Membrane Adhesion via Glycolipids Occurs for Abundant Saccharide Chemistries

Membrane-bound oligosaccharides with specific chemistries are known to promote tight adhesion between adjacent membranes via the formation of weak saccharide bonds. However, in the literature, one can find scattered evidence that other, more abundant saccharide chemistries exhibit similar behavior. Here, the influence of various glycolipids on the interaction between adjacent membranes is systematically investigated with the help of small- and wide-angle x-ray scattering and complementary neutron diffraction experiments. Added electrostatic repulsion between the membrane surfaces is used to identify the formation of saccharide bonds and to challenge their stability against tensile stress. Some of the saccharide headgroup types investigated are able to bind adjacent membranes together, but this ability has no significant influence on the membrane bending rigidity. Our results indicate that glycolipid-mediated membrane adhesion is a highly abundant phenomenon and therefore potentially of great biological relevance.     

Surface chemistry and reactivity of bacteriogenic iron oxides from Axial Volcano, Juan de Fuca Ridge, north-east Pacific Ocean

Iron oxides were collected from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge. Mineralogical inspection using X‐ray diffraction (XRD) revealed the majority of samples to be 2‐line ferrihydrite, with one of the samples corresponding to poorly ordered goethite. Examination using environmental scanning electron microscopy (ESEM) found the constituents of the iron oxides to consist predominantly of bacterial‐like structures that resembled the iron oxidizing bacteria Leptothrix ochracea, Gallionella ferruginea and a novel PV‐1 strain. X‐ray photoelectron spectroscopy (XPS) detected the presence of Fe, O, C, N, Ca, Si and P on all the samples with the exception of poorly ordered goethite, where Ca and P were absent, in addition to a weak N peak. Binding energy shifts of the Fe 2p and O 1s peaks were indicative of ferrihydrite and hydroxyl functional groups, while the presence and speciation of the C 1s peak was attributed to the presence of bacteria. Use of acid‐base titration data modelling in conjunction with a linear programming regression method (LPM) indicated that the iron oxides are composed of heterogeneous surface functional groups. Differences in iron oxide reactivity values correlated with differences in the bacterial and mineral fabric of the samples. The diverse surface chemistry and high reactivity of these iron oxides may be important in the global cycling of various elements throughout the oceans due to their presence along widespread mid‐ocean ridges.     

Sorption of Fe (hydr)oxides to the surface of Shewanella putrefaciens: cell-bound fine-grained minerals are not always formed de novo.

Shewanella putrefaciens, a gram-negative, facultative anaerobe, is active in the cycling of iron through its interaction with Fe (hydr)oxides in natural environments. Fine-grained Fe precipitates that are attached to the outer membranes of many gram-negative bacteria have most often been attributed to precipitation and growth of the mineral at the cell surface. Our study of the sorption of nonbiogenic Fe (hydr)oxides revealed, however, that large quantities of nanometer-scale ferrihydrite (hydrous ferric oxide), goethite (alpha-FeOOH), and hematite (alpha-Fe(2)O(3)) adhered to the cell surface. Attempts to separate suspensions of cells and minerals with an 80% glycerin cushion proved that the sorbed minerals were tightly attached to the bacteria. The interaction between minerals and cells resulted in the formation of mineral-cell aggregates, which increased biomass density and provided better sedimentation of mineral Fe compared to suspensions of minerals alone. Transmission electron microscopy observations of cells prepared by whole-mount, conventional embedding, and freeze-substitution methods confirmed the close association between cells and minerals and suggested that in some instances, the mineral crystals had even penetrated the outer membrane and peptidoglycan layers. Given the abundance of these mineral types in natural environments, the data suggest that not all naturally occurring cell surface-associated minerals are necessarily formed de novo on the cell wall.     

On the role of calcium in adhesion of cells to solid substrates.

Experiments are described which show that while the presence of calcium in the medium is required for the cells to maintain their adhesion, it is not necessary for the initial attachment of 3T3 cells to solid substrates. Cells are detached by treatment with urea at 4 degrees C suggesting that adhesion may involve hydrogen bonding between the cell surface and the substratum. Although most of the cell-bound calcium is removed by trypsin, the detaching effect of trypsinisation can be inhibited at low temperature suggesting that ionic calcium bridges are probably not directly involved in retaining the cells on the surface. Cells are made totally insensitive to removal by trypsin by prior washing with lanthanum. Our findings suggest that the external role of calcium in cell adhesion is exerted indirectly. We conclude that the cell presents to the exterior at least two physiochemical classes of molecule. One class composed of hydrogen bond-forming adhesive material (possible proteins) and another class of anti-adhesive molecules (possibly glycoproteins). These two components are somehow separated in the formation of adhesive 'plaques' and this process is process is apparently uninfluenced by the calcium concentration in the medium. However, the maintenance of the localised zones of adhesion is aided by factors which prevent their disruption by the intrusion into them of anti-adhesive molecules diffusing from adjacent regions of the cell membrane. These factors include cooling below the transition temperature of the membrane lipids and lateral cross-linking of non-adhesive elements by calcium. By contrast, conditions which reduce the stability of the separation of adhesive and non-adhesive surface components would be expected to diminish the overall adhesiveness of cells to the substratum.     

Morphology of cell-substratum adhesion

Many cell types modulate growth, differentiation, and motility through changes in cell substrate adhesion, including regulation of focal contact formation. Clustering of cell surface adhesion receptors is an essential early step in the development of focal contacts, and thus may influence cell physiology. In this paper, we present a theoretical framework to examine how cell surface chemistry affects receptor clustering. Our one-dimensional tape-peeling model couples the equations of mechanical equilibrium for a cell membrane with kinetic receptor-ligand binding relations. We considered two distinct model scenarios: Adhesion mediated by multiple receptor-ligand interactions of different length and specific binding of a single receptor type occurs in the presence of van der Waals attraction and nonspecific repulsion. In each case, nonuniform (wave-like) membrane morphologies are observed in certain parameter ranges that support the clustering of adhesion receptors. The formation of these morphologies is described in terms of a balance of membrane stresses; when cell-surface potential as a function of separation distance is symmetric between two potential energy minima, nonuniform morphologies are obtained. Increases in the chemical binding energy between receptor and ligand (e.g., increases in ligand density) or decreases in the membrane rigidity result in smaller wavelengths for nonuniform interfaces. Additionally, we show wave-like geometries appear only when the mechanical compliance of receptor-ligand bonds is within an intermediate range, and examine how the mobility of “repellers”—glycocalyx molecules that exert a nonspecific repulsive force—influences membrane morphology. We find fully mobile repellers always redistribute to prevent nonuniform morphologies.     

Limited reduction of ferrihydrite encrusted by goethite in freshwater sediment

Many physical and chemical processes control the extent of Fe(III) oxyhydroxide reduction by dissimilatory Fe(III)‐reducing bacteria. The surface precipitation of secondary Fe minerals on Fe(III) oxyhydroxides limits the extent of microbial Fe(III) reduction, but this phenomenon has not yet been observed in nature. This paper reports the observation of secondary Fe‐mineral (goethite) encrustation on ferrihydrite surface within freshwater sediment up to 10 cm deep. The sediment surface was characterized by the predominance of ferrihydrites with biogenic stalks and sheaths. An Fe(II)‐oxidizing bacterium (Gallionellaceae) was detected by 16S rRNA gene analysis at sediment depths of 1 and 2 cm. Fe²⁺ concentration in the sediment pore water was relatively higher at 2–4 cm depths. The 16S rRNA genes affiliated with dissimilatory Fe(III)‐reducing bacteria were detected at 1, 2, and 4 cm depths. The results of the Fe K‐edge extended X‐ray absorption fine structure (EXAFS) analysis suggested the presence of goethite and siderite at depths below 3 cm. However, the change in the Fe‐mineral composition was restricted to sediment depths between 3 and 4 cm, despite the presence of abundant ferrihydrite at depths below 4 cm. An increase in CH₄ concentration was observed at deeper than 6 cm. Stable isotopic analysis of CH₄ in the pore water indicated that acetoclastic CH₄ occurred at depths below 7 cm. Transmission electron microscope observations suggested the presence of goethite and siderite on stalks and sheaths at depths below 3 cm. Results from conversion electron yield EXAFS analysis suggested that goethite dominated at 10 cm depth, thereby indicating that ferrihydrite was encrusted by goethite at this depth. Moreover, the incomplete reduction of ferrihydrite below depths of 4 cm was not due to the lack of organic carbon, but was possibly due to the surface encrustation of goethite on ferrihydrite.     

Contributions of lipids and proteins to the surface charge of membranes. An electron microscopy study with cationized and anionized ferritin

The surface charge of cultured neurons was investigated with the electron microscope markers anionized ferritin (AF) and cationized ferritin (CF). To determine which membrane components could react with the markers, model reactions were used. Both protein-coated Sepharose beads and lipid vesicles were reacted at physiological pH. Results with these model reactions indicate that the following groups may contribute to the surface charge: acidic groups--the sialic acid of both glycoproteins and gangliosides, the carboxyl group of proteins, and the phosphates of phospholipids; basic groups--the amines of proteins. The effect of chemical fixation on the surface charge was investigated. Glutaraldehyde fixation was shown to increase the charge of neutral proteins but not by a mechanism involving unbound aldehydes. Glutaraldehyde fixation of phospholipid vesicles in the presence of CF showed that amine-containing phospholipids were cross-linked to CF. This cross-linkage was seen with the electron microscope as the clumping of CF and the burying of CF in the membrane. Paraformaldehyde fixation had a lesser effect on the charge of proteins but did react with phospholipids as did glutaraldehyde. It is concluded that at physiological pH: (a) most of the charged proteins and lipids on cell surface can contribute to the membrane surface charge, and (b) the membrane surface charge of cells can be greatly changed by chemical fixation.     

Surface alteration of realgar (As4S4) by Acidithiobacillus ferrooxidans

The chemical and physical characteristics of realgar (an arsenic sulfide mineral that occurs in several crystalline forms) in the presence of Acidithiobacillus ferrooxidans BY-3 were investigated in this work. Grains of the mineral were incubated for 10, 20, and 30 days with A. ferrooxidans cultured in 9K medium at 30 °C and at 150 rpm agitation. Abiotic control experiments were conducted in identical solutions. The effect of bioleaching on the surface properties of realgar was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), inductively coupled plasma atomic emission spectroscope (ICP-AES), X-ray diffraction (XRD), and Raman spectroscopy. SEM and EDS analyses confirmed the ability of A. ferrooxidans to modify surfaces of realgar and to efficiently enhance its dissolution. ICP-AES showed the dissolution and precipitation of realgar during bioleaching. Based on the XRD pattern and the Raman spectra, the decrease in arsenic in the liquid phase was due to co-precipitation of the mineral with Fe(III) or Fe(III) compounds (e.g., jarosite or goethite). Thus, not only did Fe(III) alter the surface of realgar, but it also promoted its dissolution during bioleaching.     

Sorption of Fe (Hydr)Oxides to the Surface of Shewanella putrefaciens: Cell-Bound Fine-Grained Minerals Are Not Always Formed De Novo

Shewanella putrefaciens, a gram-negative, facultative anaerobe, is active in the cycling of iron through its interaction with Fe (hydr)oxides in natural environments. Fine-grained Fe precipitates that are attached to the outer membranes of many gram-negative bacteria have most often been attributed to precipitation and growth of the mineral at the cell surface. Our study of the sorption of nonbiogenic Fe (hydr)oxides revealed, however, that large quantities of nanometer-scale ferrihydrite (hydrous ferric oxide), goethite (α-FeOOH), and hematite (α-Fe₂O₃) adhered to the cell surface. Attempts to separate suspensions of cells and minerals with an 80% glycerin cushion proved that the sorbed minerals were tightly attached to the bacteria. The interaction between minerals and cells resulted in the formation of mineral-cell aggregates, which increased biomass density and provided better sedimentation of mineral Fe compared to suspensions of minerals alone. Transmission electron microscopy observations of cells prepared by whole-mount, conventional embedding, and freeze-substitution methods confirmed the close association between cells and minerals and suggested that in some instances, the mineral crystals had even penetrated the outer membrane and peptidoglycan layers. Given the abundance of these mineral types in natural environments, the data suggest that not all naturally occurring cell surface-associated minerals are necessarily formed de novo on the cell wall.     

Characterization of the outer membrane protein OprF of Pseudomonas aeruginosa in a lipopolysaccharide membrane by computer simulation

The N-terminal domain of outer membrane protein OprF of Pseudomonas aeruginosa forms a membrane spanning eight-stranded antiparallel beta-barrel domain that folds into a membrane channel with low conductance. The structure of this protein has been modeled after the crystal structure of the homologous protein OmpA of Escherichia coli. A number of molecular dynamics simulations have been carried out for the homology modeled structure of OprF in an explicit molecular model for the rough lipopolysaccharide (LPS) outer membrane of P. aeruginosa. The structural stability of the outer membrane model as a result of the strong electrostatic interactions compared with simple lipid bilayers is restricting both the conformational flexibility and the lateral diffusion of the porin in the membrane. Constricting side-chain interactions within the pore are similar to those found in reported simulations of the protein in a solvated lipid bilayer membrane. Because of the strong interactions between the loop regions of OprF and functional groups in the saccharide core of the LPS, the entrance to the channel from the extracellular space is widened compared with the lipid bilayer simulations in which the loops are extruding in the solvent. The specific electrostatic signature of the LPS membrane, which results in a net intrinsic dipole across the membrane, is found to be altered by the presence of OprF, resulting in a small electrically positive patch at the position of the channel.     

Local coupling of respiration processes and phosphorylation in rat liver mitochondria

One variant of the model of the local coupling of phosphorylation and respiration in intact mitochondria was experimentally verified. The model is based on the following postulates: (1). Upon the functioning of H+ pumps, hydrogen ions bound to the outer membrane surface do not enter the aqueous phase but are utilized for ATP synthesis in the membrane supercomplex respiratory H+ pump--ATP synthetase. (2). During the functioning of H+ pumps, an appreciable part of the energy of oxidation reactions can be stored in the form of the thermodynamic (solvation) potential of H+ ions bound to the outer membrane surface. According to the model, the hydration of hydrogen ions during the transition from the outer face of the inner membrane to the aqueous phase should lead to a decrease in the efficiency of the system of the coupling of respiration and phosphorylation. The model takes into account the ability of the nonpermeating buffer to catalyze the detachment of hydrogen ions from the membrane surface to the aqueous phase and provide their complete solvation. A preparation of phosphorylating mitochondria with the covalently bound pH probe was obtained. This made it possible to register for the first time the presence of a local H+ gradient on the outer side of the inner mitochondrial membrane during the stable functioning of the oxidative phosphorylation system. It was shown on these mitochondrial preparations that a decrease in the outer local H+ gradient by the action of increased concentrations of buffer is accompanied by a significant decrease in the ADP/O parameter and a partial dissociation of oxidative phosphorylation. Conditions were determined under which increased concentrations of buffer in the incubation medium cause a partial dissociation and a decrease in the ADP/O value from 20% to twofold (depending on the quality of mitochondrial preparations). The results obtained are in full agreement with the predictions of the model.     

Fimbriae mediated nonspecific adhesion of Salmonella typhimurium to mineral particles

The adhesion of cells of Salmonella typhimurium to albite, biotite, felspar, magnetite and quartz was correlated to the presence of fimbriae and degree of hydrophobicity and charge of the bacterial surface. It was found that the presence of fimbriae resulted in a higher degree of adhesion compared to adhesion of nonfimbriated cells. The significance of the physico-chemical characteristics of fimbriae was shown by a direct linearity between high hydrophobicity of fimbriated cells and degree of adhesion to the mineral particles. Fimbriated cells exhibited higher negative as well as positive surface charge as compared to nonfimbriated cells. Adhesion to several of the minerals was shown to be independent of the extent of negative charges on the bacterial surfaces. A high degree of adhesion to biotite, possibly due to a combination of characteristics of the particles, was not related to either bacterial fimbriation or a physico-chemical characteristic of the bacterial surface. The results of the nonspecific adhesion observed are discussed in terms of available binding sites and distribution of physico-chemical characteristics on the bacterial cell surface structures.