Relative surface charge, hydrohobicity of bacterial cells and their affinity to substrate during copper bioleaching from post-flotation wastes

Exopolymers produced by bacteria cells during copper bioleaching from copper sulphides could modify the relative cell surface charge and thus change the relation between cell and substratum surfaces. All examined bacterial strains showed a hydrophilic cell surface independent of relative surface charge and adhesion depended on presence or absence of exopolymer. The effect of exopolymers on adhesion processes differed according to the strain and was clearer in the case of pure culture. © Rapid Science Ltd. 1998     

Correlation between localized anodic areas and Oceanospirillum biofilms on copper

The marine bacterium Oceanospirillum produces copious amounts of exopolymer when grown on copper surfaces and binds Cu⁺² from the substratum. The organism and associated exopolymers result in local anodic regions that can be detected by scanning vibrating electrode microscopy. Oceanospirillum was grown in small laminar flow cells with two carbon sources on copper and 316 stainless steel as substrata. The chemical composition of the exopolymer varied with growth medium, but not with substratum. Exopolymers from cells grown in glutamic acid medium on both substrata contained glucose with no other sugar monomers or uronic acids. The quantity of exopolymer did vary with substratum and copper promoted greater polymer production that stainless steel.     

The role of exopolymers in the attachment of sphingomonas paucimobilis

The importance of exopolymers in the adhesion of Sphingomonas paucimobilis was established by studying the attachment to glass of three mutants with defective gellan production. The attachment assays were performed in either phosphate buffered saline (controls) or in the exopolymeric solutions produced by the mutants. The exopolymer was found to have surface active properties, changing the glass surface from hydrophilic to hydrophobic, making adhesion thermodynamically favourable. Only the cells that had a substantial polymeric layer surrounding their walls were able to significantly colonise glass coated with the exopolymer. It is hypothesised that the exopolymer bound to the glass and the exopolymer present at the surface of the bacteria bound together, overcoming the energy barrier created by the negative charge of both surfaces. It is concluded that the exopolymer from S. paucimobilis has a dual role in the process of adhesion by both coating the surface thereby strengthening adhesion and by enhancing adhesion through the establishment of polymeric bridges.     

Extracellular Polymer Produced in the Presence of Copper Minerals

Abstract

A qualitative and semiquantitative assay was applied to estimate production of peripheral exopolymers by strains of bacteria isolated from flotation wastes during growth on copper sulphides and copper minerals wastes at neutral pH. Exopolymer production, expressed as percentage of Alcian Blue adsorption per μ g of cell protein, was the lowest on a complete organic medium and the highest on a nutrient-limited mineral medium. The exopolymer was highly resistant to acid hydrolysis and contained hydrocarbons, saturated and unsaturated fatty acids, aromatic acids and aromatic acid esters, which are well known as artificial surfactants and plasticizers. Carbohydrates appeared incidentally and in trace amount only. Chemical components of the exopolymer or chemically similar compounds also were found in black shale particles in the flotation wastes.     

Attachment Stimulates Exopolysaccharide Synthesis by a Bacterium

This study examined the hypothesis that solid surfaces may stimulate attached bacteria to produce exopolymers. Addition of sand to shake-flask cultures seemed to induce exopolymer synthesis by a number of subsurface isolates, as revealed by optical microscopy. Several additional lines of evidence indicated that exopolymer production by attached cells (in continuous-flow sand-packed columns) was greater than by their free-living counterparts. Total carbohydrates and extracellular polysaccharides, both normalized to cell protein, were greater (2.5- and 5-fold, respectively) for attached cells than for free-living cells. Also, adsorption of a polyanion-binding dye to the exopolymer fraction was sixfold greater for attached cells than for unattached cells. When surface-grown cells were resuspended in fresh medium, exopolymer production decreased to the level characteristic of unattached cells, which ruled out the possibility that attached cells comprised a subpopulation of sticky mucoid variants. The mechanism by which attachment stimulated exopolymer synthesis did not involve changes of the specific growth rate, growth stage, or limiting nutrient.     

Biosynthesis of novel exopolymers by Aureobasidium pullulans

Aureobasidium pullulans ATCC 42023 was cultured under aerobic conditions with glucose, mannose, and glucose analogs as energy sources. The exopolymer extracts produced under these conditions were composed of glucose and mannose. The molar ratio of glucose to mannose in the exopolymer extract and the molecular weight of the exopolymer varied depending on the energy source and culture time. The glucose content of exopolymer extracts formed with glucose and mannose as the carbon sources was between 91 and 87%. The molecular weight decreased from 3.5 x 10(6) to 2.12 x 10(6) to 0.85 x 10(6) to 0.77 x 10(6) with culture time. As the culture time increased, the glucose content of the exopolymer extract formed with glucosamine decreased from 55 +/- 3 to 29 +/- 2 mol%, and the molecular weight increased from 2.73 x 10(6) to 4.86 x 10(6). There was no evidence that glucosamine was directly incorporated into exopolymers. The molar ratios of glucose to mannose in exopolymer extracts ranged from 87 +/- 3:13 +/- 3 to 28 +/- 2:72 +/- 2 and were affected by the energy source added. On the basis of the results of an enzyme hydrolysis analysis of the exopolymer extracts and the compositional changes observed, mannose (a repeating unit) was substituted for glucose, which gave rise to a new family of exopolymer analogs.     

The redistribution of fungicides on plants

In field trials amounts of soluble copper were found in rain water collected form apple trees sprayed with copper fungicides, but the copper was relatively non-toxic. The solution of copper did not appear to be correlated with the number of micro-organisms on the leaves. Rain washings phate. Some evidence for beneficial redistribution by solution is presented. By contrast, in a greenhouse experiment small amounts of copper were washed by very light rain from coffee seedlings sprayed with copper oxychloride and Bordeaux mixture. The soluble fraction of these washings was generally small and did not vary with ageing of the deposit up to 32 days. There was no changes in the toxicity of the washings from deposits aged up to 32 days. Under static laboratory conditions more copper was usually solubilized form standardized deposits of Bordeaux mixture, copper oxychloride, and cuprous oxide on leaves than on glass. The amount of copper solubilized varied with the leaf used, the nature of the deposit, the presence of adjuvants and the length of time water was left in contact with the deposit. Deposits of Bordeaux mixture and Bordeaux mixture was equally toxic on a leaf surface which caused solution and one which did not. Soluble copper extracts leaves were less toxic than equivalent quantities of copper supplied as copper sulphate.     

The Role of Exopolymers Produced by Sphingomonas paucimobilis in Biofilm Formation and Composition

Exopolymers have been associated with the initial adhesion of bacteria, which is the primary step for biofilm formation. Moreover, the polymeric matrix of biofilms has a considerable influence on some of the most important physical and physiological properties of biofilms. The role of extracellular polymers in biofilm formation was studied using three mutants of Sphingomonas paucimobilis with increasing capabilities for exopolymer production. The physical, biochemical and physiological properties of three different layers of each biofilm were determined. The layers were detached by submitting the biofilm to increasing shear stress. The results revealed that the presence of exopolymers in the growth medium was essential for biofilm formation. The mutant producing the highest amount of exopolymer formed very thick biofilms, while the biofilms formed by the medium exopolymer producer were on average 8 times thinner. The lowest exopolymer producer did not form biofilm. In both types of biofilms, exopolymer density increased with depth, although this tendency was more significant in thinner biofilms. Cell distribution was also more heterogeneous in thinner biofilms, exhibiting a greater accumulation of cells in the inner layers. The thicker biofilms had very low activity in the inner layer. This was related to a high accumulation of proteins and DNA in this layer due to cell lysis and hydrolytic activity. Activity in the thin biofilm was constant throughout its depth, suggesting that there was no nutrient limitation. The production of exopolymers by each cell was constant throughout the depth of the biofilms, although it was greater in the case of the higher producer.     

Molecular characterization of acutely and gradually heavy metal acclimated aquatic bacteria by FTIR spectroscopy

In the environment, bacteria can be exposed to the concentration gradient of toxic heavy metals (gradual) or sudden high concentration of them (acute). In both situations, bacteria get acclimated to toxic heavy metal concentrations. Acclimation causes metabolic and molecular changes in bacteria. In this study, we aimed to understand whether there are differences between molecular profiles of the bacteria (Brevundimonas, Gordonia and Microbacterium) which are under acute or gradual exposure to cadmium or lead by using ATR‐FTIR spectroscopy. Our results revealed the differences between the acclimation groups in membrane dynamics including changes in the structure and composition of the membrane lipids and proteins. Furthermore, protein concentrations decreased in acclimated bacterial groups. Also, a remarkable increase in exopolymer production occurred in acclimated groups. Interestingly, bacteria under acute cadmium exposure produced the significantly higher amount of exopolymer than they did under gradual exposure. On the contrary, under lead exposure gradually acclimate strains produced significantly higher amounts of exopolymer than those of acutely acclimated ones. This information can be used in bioremediation studies to obtain bacterial strains producing a higher amount of exopolymer.      

Mechanisms of cadmium resistance in anaerobic bacterial enrichments degrading pentachlorophenol

The mechanisms of heavy-metal resistance used by adapted sulfidogenic and methanogenic enrichments degrading pentachlorophenol in the presence of cadmium (Cd) were studied. The enrichment cultures adapted to and readily tolerated bioavailable Cd concentrations up to 50 ppm while degrading an equal concentration of pentachlorophenol. Both cultures removed >95% of the Cd from solution. Transmission electron micrographs revealed (i). the presence of electron-dense particles surrounding the cells in the sulfidogenic enrichments and (ii). the unusual clumping of cells and the presence of an exopolymer in the methanogenic enrichments. Energy dispersive X-ray analysis showed that the sulfidogenic enrichments removed Cd by extracellular precipitation of cadmium sulfide, while the methanogenic enrichment culture removed Cd by extracellular sequestration of Cd into the exopolymer.     

Exopolymer Biosynthesis and Proteomic Changes of Pseudomonas sp. HK-6 Under Stress of TNT (2,4,6-Trinitrotoluene)

Scanning electron microscopy revealed pores and wrinkles on the surface of Pseudomonas sp. HK-6 cells grown in Luria Bertani (LB) medium containing 0.5 mM TNT (2,4,6-trinitrotoluene). Exopolymer connections were also observed on the wild-type HK-6 cells but not on the algA mutant cells. In addition, the amount of exopolymer from HK strain increased from 90 to 210 microg/mL under TNT stress, whereas the algA mutant produced approximately 30 microg/mL, and its exopolymer production was little increased by TNT stress. These results indicate that TNT stress induced exopolymer production with alginate as a major component. The algA mutant degraded TNT more slowly than the wild-type HK-6 strain. HK-6 was able to completely degrade 0.5 mM TNT within 8 days, whereas algA mutant only achieved approximately 40% within the same time period. Even after 20 days, no more than 80% of TNT was degraded. According to analyses of proteomes of HK-6 and algA mutant cells grown under TNT stress or no stress, several proteins (KinB, AlgB, Alg8, and AlgL) in alginate biosynthesis were only highly induced by both strains under TNT stress. Interestingly, two stress-shock proteins (SSPs), GroEL and RpoH, were more highly expressed in the algA mutant than the HK-6 strain. The algA mutant was rendered more vulnerable to environmental stress and had reduced ability to metabolize TNT in the absence of alginate synthesis.     

Transport of copper and manganese to the xylem exudate of sunflower

Abstract Absorption of copper and manganese by sunflower roots from solution cultures of varying composition was followed by measuring the concentrations of the metals appearing in whole roots, root cell sap and xylem exudate. Total copper in the fibrous roots was linearly related to the concentration of copper in the external solution but the concentration of copper released to the xylem exudate was buffered somewhat against the changes made externally. No such buffering was observed for managenese. A copper-sensitive electrode, responsive only to free cupric ions was used in conjunction with total copper analysis by atomic absorption spectrophotometry to show that little of the copper (usually < 1%) existed as a free ion in any phase of the system. Copper in the xylem exudate may be strongly complexed. An electron paramagnetic resonance spectrum of the xylem exudate indicated that manganese probably was a free divalent ion. Calculation of the electrochemical potential gradient for free cupric ions showed that no special metabolically-linked mechanism need be postulated to account for absorption of copper (or manganese) other than that necessary to maintain the transmembrane potential.     

Biosynthesis of Novel Exopolymers by Aureobasidium pullulans

Aureobasidium pullulans ATCC 42023 was cultured under aerobic conditions with glucose, mannose, and glucose analogs as energy sources. The exopolymer extracts produced under these conditions were composed of glucose and mannose. The molar ratio of glucose to mannose in the exopolymer extract and the molecular weight of the exopolymer varied depending on the energy source and culture time. The glucose content of exopolymer extracts formed with glucose and mannose as the carbon sources was between 91 and 87%. The molecular weight decreased from 3.5 × 10⁶ to 2.12 × 10⁶ to 0.85 × 10⁶ to 0.77 × 10⁶ with culture time. As the culture time increased, the glucose content of the exopolymer extract formed with glucosamine decreased from 55 ± 3 to 29 ± 2 mol%, and the molecular weight increased from 2.73 × 10⁶ to 4.86 × 10⁶. There was no evidence that glucosamine was directly incorporated into exopolymers. The molar ratios of glucose to mannose in exopolymer extracts ranged from 87 ± 3:13 ± 3 to 28 ± 2:72 ± 2 and were affected by the energy source added. On the basis of the results of an enzyme hydrolysis analysis of the exopolymer extracts and the compositional changes observed, mannose (a repeating unit) was substituted for glucose, which gave rise to a new family of exopolymer analogs.     

Dissolved organic carbon and bacterial populations in the gelatinous surface microlayer of a Norwegian fjord mesocosm

The sea surface microlayer is the interfacial boundary layer between the marine environment and the troposphere. Surface microlayer samples were collected during a fjord mesocosm experiment to study microbial assemblage dynamics within the surface microlayer during a phytoplankton bloom. Transparent exopolymer particles were significantly enriched in the microlayer samples, supporting the concept of a gelatinous surface film. Dissolved organic carbon and bacterial cell numbers (determined by flow cytometry) were weakly enriched in the microlayer samples. However, the numbers of Bacteria 16S rRNA genes (determined by quantitative real-time PCR) were more variable, probably due to variable numbers of bacterial cells attached to particles. The enrichment of transparent exopolymer particles in the microlayer and the subsequent production of a gelatinous biofilm have implications on air–sea gas transfer and the partitioning of organic carbon in surface waters.     

Studies on the adsorption and availability of copper in some arid soils

Summary Eight texturally different arid soils have been studied for the adsorption reactions of copper and thereby evaluated for their quantity, intensity and supply parameters for the copper. In these soils with the addition of increasing amounts of copper there was increase in the equilibrium concentration, adsorption, per cent saturation of adsorption capacity and supply parameter of copper. However, negative relationship of differential buffering capacity with quantity, intensity and supply parameters revealed that the sandy loam soils exhibited comparatively more resistance to change in the solution concentration of copper. Multiple regression analysis revealed that in all soils quantity, intensity and differential buffering capacity were the sole parameters accounting for the supply of the nutrient. Sandy loam soils having comparatively higher values for the adsorption maxima, bonding energy constant and differential buffering capacity of the soils required higher doses of applied copper to change in the solution concentration than in sandy soils.     

Monosaccharide composition of exopolymer complex in Thiobacillus thioparus and Stenotrophomonas maltophilia

The bacteria of Thiobacillus thioparus and Stenotrophomonas maltophilia are capable to form a thick biofilm complicated as to its structure on the surface of low-carbon steel. This biofilm formation on any surface occurs under the adhesion of the cells of the plankton growth model with the help of synthesis of muciferous exopolymers with adhesive properties. Hence the monosaccharide composition of the exopolymer complex in the form of polyol acetates was studied by chromate-mass-spectrum method. A significant difference in the composition of exopolymer monosaccharides with the presence of steel model in the medium and without it was established; a change in the monosaccharide composition of mono- and binary culture in the conditions of plankton and biofilm growth was also observed.     

Copper-binding characteristics of exopolymers from a freshwater-sediment bacterium.

Copper-binding activity by exopolymers from adherent cells of a freshwater-sediment bacterium was demonstrated by a combination of equilibrium dialysis and flameless atomic absorption spectrometry. Crude, cell-free exopolymer preparations containing protein and polysaccharide components bound up to 37 nmol of Cu per mg (dry weight). A highly purified exopolysaccharide preparation bound up to 253 nmol of Cu per mg of carbohydrate. The conditional stability constant for the crude exopolymer-Cu complex was 7.3 X 10(8). This value was similar to those obtained for Cu complexes formed with humic acids and xanthan, an exopolysaccharide produced by Xanthomonas campestris. Studies conducted at copper concentrations, pHs, and temperatures found in sediments from which the bacterium was isolated indicated that the exopolymers were capable of binding copper under natural conditions.     

Copper-binding characteristics of exopolymers from a freshwater-sediment bacterium

Copper-binding activity by exopolymers from adherent cells of a freshwater-sediment bacterium was demonstrated by a combination of equilibrium dialysis and flameless atomic absorption spectrometry. Crude, cell-free exopolymer preparations containing protein and polysaccharide components bound up to 37 nmol of Cu per mg (dry weight). A highly purified exopolysaccharide preparation bound up to 253 nmol of Cu per mg of carbohydrate. The conditional stability constant for the crude exopolymer-Cu complex was 7.3 X 10(8). This value was similar to those obtained for Cu complexes formed with humic acids and xanthan, an exopolysaccharide produced by Xanthomonas campestris. Studies conducted at copper concentrations, pHs, and temperatures found in sediments from which the bacterium was isolated indicated that the exopolymers were capable of binding copper under natural conditions.     

Estimation of conditional stability constant for copper binding to fish gill surface with consideration of chemistry of the fish gill microenvironment

Binding-site concentration and conditional stability constants for copper and fish gill surface interactions were calculated based on the data from the literature. Six scenarios were modeled by including or excluding pH and alkalinity differences between the fish gill microenvironment and the bulk solution and the presence of free mucus in the calculation. We demonstrate that changes in pH or alkalinity, or both, for model input had only a slight influence on the calculated results because of the small difference in pH and alkalinity between the gill microenvironment and the bulk solution under the specific experimental conditions. Inclusion of free mucus in the model, however, led to a large change in the final results. For example, with consideration of free mucus and changes in pH and alkalinity in the model, the calculated site concentration and the stability constant were 0.022 micromol/g wet tissue and log K=8.77, respectively, compared to 0.026 micromol/g wet tissue with log K=7.78 without free mucus and pH/alkalinity change.     

Isolation of 2′-Hydroxy-4′-methoxy propiophenone from Tribolium castaneum and T confusum

The copper binding properties were influenced by growth phase of cells, pH and concentration of copper in reaction mixtures. The efficiency of copper absorption increased with growth time and was largest at the mid-logarithmic growth phase. The time course of copper absorption was biphasic, that copper rapidly bound to cell surface for initial few minutes after addition of copper and then the copper was slowly transported into cells. The copper binding to the cell surface depended on the molecular form of copper complex in the reaction mixture and the ligand residue to copper on the cell surface. Double reciprocal plots of absorption velocity of copper vs. copper concentration gave straight lines at low concentration between 0.01 to 0.1 mm. The apparent affinity of copper to the cells of stationary growth phase was the same as that of logarithmic growth phase, that is, the Km values were about 0.01 mm. On the other hand, at high concentration of copper between 0.1 to 5.0 mm the apparent affinity decreased but the absorption velocity of copper remarkably increased. Zinc sulfate most strongly inhibited the copper absorption in this test. It was assumed that zinc competitively bound to the copper binding sites of cell surface.