Showing papers on "Biofilm matrix published in 1998"

A review of experimental measurements of effective diffusive permeabilities and effective diffusion coefficients in biofilms.

Abstract: Experimental measurements of effective diffusive permeabilities and effective diffusion coefficients in biofilms are reviewed. Effective diffusive permeabilities, the parameter appropriate to the analysis of reaction-diffusion interactions, depend on solute type and biofilm density. Three categories of solute physical chemistry with distinct diffusive properties were distinguished by the present analysis. In order of descending mean relative effective diffusive permeability (De/Daq) these were inorganic anions or cations (0.56), nonpolar solutes with molecular weights of 44 or less (0.43), and organic solutes of molecular weight greater than 44 (0.29). Effective diffusive permeabilities decrease sharply with increasing biomass volume fraction suggesting a serial resistance model of diffusion in biofilms as proposed by Hinson and Kocher (1996). A conceptual model of biofilm structure is proposed in which each cell is surrounded by a restricted permeability envelope. Effective diffusion coefficients, which are appropriate to the analysis of transient penetration of nonreactive solutes, are generally similar to effective diffusive permeabilities in biofilms of similar composition. In three studies that examine diffusion of very large molecular weight solutes (>5000) in biofilms, the average ratio of the relative effective diffusion coefficient of the large solute to the relative effective diffusion coefficient of either sucrose or fluorescein was 0.64, 0.61, and 0.36. It is proposed that large solutes are effectively excluded from microbial cells, that small solutes partition into and diffuse within cells, and that ionic solutes are excluded from cells but exhibit increased diffusive permeability (but decreased effective diffusion coefficients) due to sorption to the biofilm matrix.

In situ Characterization of Biofilm Exopolymers Involved in the Accumulation of Chlorinated Organics

Abstract: The chemical nature and spatial arrangements of exopolymers in a degradative biofilm community were studied using a panel of fluorescein isothiocyanate– and tetramethyl rhodamine isothiocyanate–conjugated probes. Image analysis and dual channel imaging, in conjunction with scanning confocal laser microscopy, allowed detection and quantification of lectin binding to a variety of glycoconjugates. Relative abundance of these components varied between 0 and 67% of biofilm area at any depth. Lectin binding sites were distributed nonuniformly, both horizontally and vertically, within the >30-μm thick biofilms when the herbicide diclofop methyl was provided as the sole carbon source. A more uniform distribution of lectin binding sites was formed by the same biofilm community, when grown on a labile medium. Diclofop and its metabolites accumulated in extracellular polymers when biofilms were grown with diclofop as the sole source of carbon and energy, but not in the presence of the labile carbon source. There was a nearly 1:1 correspondence between the distribution of regions that accumulated diclofop (and other chlorinated ring compounds) and regions with binding sites for the α-l-fucose-specific Ulex europaeus Type I lectin. These regions also bound polyanionic and cationic fluor-conjugated dextrans, and a hydrophobic-specific dye, demonstrating the nonuniform distribution of charged and hydrophobic regions in the biofilm matrix. Hydrolytic enzymes, some of them selected for their specificity against residues identified by the lectin assay, had no effect on either structural integrity or diclofop binding. The distribution of diclofop binding, lectin binding, and charged regions observed in these biofilms indicated a degree of spatial organization and differentiation within the biofilm community. In addition, based on cell morphology and fluorescent gram reaction, these regions were primarily associated with one community member, a Bacillus coagulans strain.

The role of exopolysaccharides in dual species biofilm development

Abstract: A plasmid encoding the green fluorescent protein (GFP) of Aequorea Victoria was transformed into a biofilm-forming strain of Enterobacter agglomerans originally isolated from an industrial environment. The transformed strain, EntGFP, could then be identified in dual species biofilms by direct visualization, plate counts and quantitiative fluorescence measurements. A variety of cell constituents and products may be involved in the adhesion and accumulation process and exopolysaccharides (EPS) represent one of these factors. The involvement of EPS in the initial adhesion events and the role in dual species biofilm development was investigated. Cells of EntGFP and Klebsiella pneumoniae G1 interact forming biofilms more successfully in a mixture than in isolation. The co-resistance results in enhanced biofilm formation and increased resistance to disinfection. Microscopic examination showed that the two species were often closely juxtaposed in microcolonies, suggesting the interactions involve surface-associated macromolecules. Fluorescence was used to measure the adhesion of EntGFP cells to Kleb. pneumoniae G1 (G1) EPS. The results showed EntGFP adhered better to G1 EPS that Ent EPS. Polysaccharde depolymerases isolated from a bacteriophage for Ent. agglomerans were used to degrade Ent EPS specifically. Following polysaccharase treatment, the adhaesion of EntGFP to G1 cells was reduced. This suggests both types of EPS mediate adhesion. The two types of EPS were dissolved in dimethylsulphoxide and when mixed, their viscosity increased, reaching a maximum after 40 min. This may partially explain the increased protection of dual species biofilms from disinfectants. The depolymerases were used to treat dual species biofilms and this resulted in the effective removal of both species from the surface. This may suggest Ent contributes more EPS to the biofilm matrix. The EPS play an important role in EntGFP and G1 dual species biofilm formation both as adhesins and as the EPS interact, changing their physical properties.

Spatial and Temporal Deposition of Hyphomonas Strain VP-6 Capsules Involved in Biofilm Formation

Abstract: Hyphomonas strain VP-6 is a prosthecate bacterium isolated from the Guayamas vent region and is a member of a genus of primary and common colonizers of marine surfaces. It adheres to solid substrata as a first step in biofilm formation. Fine-structure microscopy and the use of specific stains and lectins reveal that it synthesizes two different extracellular polymeric substances (EPS). One is a temporally synthesized, polar holdfast EPS, and the other is a capsular EPS that is present during the complete life cycle and surrounds the entire cell, including the prosthecum. The timing and location of Hyphomonas strain VP-6 EPS elaboration correlate with adhesion to surfaces, suggesting that the EPS serves not only as the biofilm matrix but also as a primary adhesin. The temporality and polarity of VP-6 EPS expression substantially differ from those properties of Hyphomonas strain MHS-3 EPS expression.

The mobilisation of polycyclic aromatic hydrocarbons from the coal tar lining of water pipes.

Abstract: Coal-tar was commonly used as an internal lining for corrosion protection of water pipes from the 19th century up to the present. It is reported that these coatings can lead to elevated concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in the distributed drinking water. The aim of the project was to investigate the processes and mechanisms responsible for the occurrence of these substances in drinking water distribution systems. The results presented in this project showed that the occurrence of PAHs in a distribution system was linked to the presence of the disinfectants chlorine and chlorine dioxide. This dependence could be shown in the laboratory, in a pilot-scale pipe rig as well as in field investigations in a real distribution system. Generally, hostile environmental conditions for microbiological activity such as stagnation periods and anaerobic conditions could be identified as the most important factors to favour the occurrence of PAHs in the drinking water. It was clearly shown that disturbances in the hydraulic regime such as water hammers, operation of valves and rapid increases in flow velocity can result in enhanced PAH concentrations. Immediately after stagnation periods PAH concentrations increased to levels which exceeded the prescribed concentrations of the EC-guideline of 200 ng/l. In laboratory experiments it was demonstrated that the coal-tar is a substrate for the growth of biofilms. Batch experiments and reactor experiments showed that the removal of biofilm resulted in a higher leaching rate of the PAHs into the water. Experiments concerning the potential for the formation of chlorinated PAHs as disinfection by-products from the PAHs prevalent in water distributed through coal-tar lined pipes showed that their occurrence is very unlikely under conditions prevalent in water distribution systems. A theory is presented which indicates that particles adhering to the pipe walls which can be sometimes embedded in the biofilm matrix represent a major factor in the process of the mobilisation of PAHs. The destabilisation of the biofilm matrix by hostile environmental conditions (disinfectants, aerobic conditions, oxygen limitation during stagnation periods) or enhanced shear forces on the biofilm, results in the release of particles highly contaminated with PAHs.