Biofilm Depth Research Articles

Modelling antibiotic- and anti-quorum sensing treatment of a spatially-structured Pseudomonas aeruginosa population

The bacterial cell to cell signalling system known as quorum sensing (QS) is essential for the regulation of virulence in many pathogens and offers a specific biochemical target for novel antibacterial therapies. Expanding on earlier work, in which consideration was given to the primary QS system (lasR system) in a homogeneous population of the common human pathogen Pseudomonas aeruginosa, we build a simple spatial model of an early-stage P. aeruginosa biofilm subject to treatment with topically applied anti-QS drugs (of two specific kinds) and conventional antibiotics. In the case of a slowly growing biofilm we show that both kinds of anti-quorum sensing drug are effective in reducing the level of the relevant signal molecule (3-oxo-C12-homoserine lactone; henceforth AHL), in each case obtaining an explicit bound on the steady-state AHL profile in terms of a prescribed surface drug concentration. Using numerical methods, we are also able to reproduce the hysteretic phenomena exhibited by the homogeneous model, in particular showing that for each kind of anti-QS drug there is a parameter regime in which a catastrophic collapse occurs in the steady-state AHL concentration as the surface drug concentration passes some critical value; an alternative way of interpreting this result is to say that, for a prescribed surface drug concentration, there is a critical biofilm depth such that treatment is successful until this depth is reached, but fails thereafter. In the thick-biofilm limit we show that the critical concentration of each drug increases exponentially with the biofilm thickness (or, conversely, that the critical depth increases logarithmically with surface drug concentration); this is dramatically different to the behaviour observed in the corresponding homogeneous model, where the critical concentrations grow linearly with bacterial carrying capacity, and thus highlights the relative difficulty of treating a large, spatially-structured population with diffusing antibacterials.

Molecular Assessment of Inoculated and Indigenous Bacteria in Biofilms from a Pilot-Scale Perchlorate-Reducing Bioreactor

Bioremediation of perchlorate-contaminated groundwater can occur via bacterial reduction of perchlorate to chloride. Although perchlorate reduction has been demonstrated in bacterial pure cultures, little is known about the efficacy of using perchlorate-reducing bacteria as inoculants for bioremediation in the field. A pilot-scale, fixed-bed bioreactor containing plastic support medium was used to treat perchlorate-contaminated groundwater at a site in Southern California. The bioreactor was inoculated with a field-grown suspension of the perchlorate-respiring bacterium Dechlorosoma sp. strain KJ and fed groundwater containing indigenous bacteria and a carbon source amendment. Because the reactor was flushed weekly to remove accumulated biomass, only bacteria capable of growing in biofilms in the reactor were expected to survive. After 26 days of operation, perchlorate was not detected in bioreactor effluent. Perchlorate remained undetected by ion chromatography (detection limit 4 mug L(-1)) during 6 months of operation, after which the reactor was drained. Plastic medium was subsampled from top, middle, and bottom locations of the reactor for shipment on blue ice and storage at -80 degrees C prior to analysis. Microbial community DNA was extracted from successive washes of thawed biofilm material for PCR-based community profiling by 16S-23S ribosomal intergenic spacer analysis (RISA). No DNA sequences characteristic of strain KJ were recovered from any RISA bands. The most intense bands yielded DNA sequences with high similarities to Dechloromonas spp., a closely related but different genus of perchlorate-respiring bacteria. Additional sequences from RISA profiles indicated presence of representatives of the low G+C gram-positive bacteria and the Cytophaga-Flavobacterium-Bacteroides group. Confocal scanning laser microscopy and fluorescence in situ hybridization (FISH) were also used to examine biofilms using genus-specific 16S ribosomal RNA probes. FISH was more sensitive than RISA profiling in detecting possible survivors from the initial inoculum. FISH revealed that bacteria hybridizing to Dechlorosoma probes constituted <1% of all cells in the biofilms examined, except in the deepest portions where they represented 3-5%. Numbers of bacteria hybridizing to Dechloromonas probes decreased as biofilm depth increased, and they were most abundant at the biofilm surface (23% of all cells). These spatial distribution differences suggested persistence of low numbers of the inoculated strain Dechlorosoma sp. KJ in parts of the biofilm nearest to the plastic medium, concomitant with active colonization or growth by indigenous Dechloromonas spp. in the biofilm exterior. This study demonstrated the feasibility of post hoc analysis of frozen biofilms following completion of field remediation studies.

Seasonal Changes in the Structure of RBC Heterotrophic Biofilms

Heterotrophic Biofilms, growing in the successive three treatment stages of the RBC reactor in a full-scale wastewater treatment plant in the summer of 2002, were investigated and compared to those growing in the fall of 2001. The seasonal changes in biofilm structure were studied in terms of biofilm thickness, dry solid density, internal pore distribution and patterns, and surface roughness. The comparison results indicated that due to the higher wastewater flow rate in the summer of 2002, these biofilms had thinner, denser and less rugged surface structure than the biofilms sampled in the fall of 2001; furthermore, they showed less heterogeneous internal pore distribution. However, biofilms from both seasons showed some similarities: biofilms in the treatment stages 2 and 3 had similar structure; and their internal pore distribution and pore surface roughness didn't show any correlation with the biofilm depth.

Stratification of activity and bacterial community structure in biofilms grown on membranes transferring oxygen.

Previous studies have shown that membrane-aerated biofilm (MAB) reactors can simultaneously remove carbonaceous and nitrogenous pollutants from wastewater in a single reactor. Oxygen is provided to MABs through gas-permeable membranes such that the region nearest the membrane is rich in oxygen but low in organic carbon, whereas the outer region of the biofilm is void of oxygen but rich in organic carbon. In this study, MABs were grown under similar conditions but at two different fluid velocities (2 and 14 cm s(-1)) across the biofilm. MABs were analyzed for changes in biomass density, respiratory activity, and bacterial community structure as functions of biofilm depth. Biomass density was generally highest near the membrane and declined with distance from the membrane. Respiratory activity exhibited a hump-shaped profile, with the highest activity occurring in the middle of the biofilm. Community analysis by PCR cloning and PCR-denaturing gradient gel electrophoresis of 16S rRNA genes demonstrated substantial stratification of the community structure across the biofilm. Population profiles were also generated by competitive quantitative PCR of gene fragments specific for ammonia-oxidizing bacteria (AOB) (amoA) and denitrifying bacteria (nirK and nirS). At a flow velocity of 14 cm s(-1), AOB were found only near the membrane, whereas denitrifying bacteria proliferated in the anoxic outer regions of the biofilm. In contrast, at a flow velocity of 2 cm s(-1), AOB were either not detected or detected at a concentration near the detection limit. This study suggests that, under the appropriate conditions, both AOB and denitrifying bacteria can coexist within an MAB.

Demineralization of Dentin by Streptococcus mutans Biofilms Grown in the Constant Depth Film Fermentor

To develop a bacterial demineralization model, we grew Streptococcus mutans biofilms in a constant depth film fermentor (CDFF) and studied the effects of sucrose pulsing frequency (SPF) in time on dentin demineralization. S. mutans biofilms were grown in dentin specimens with grooves and on dentin surface specimens for 20 days. During the experiments, 2% sucrose was pulsed either 4 or 8 times per day for periods of 30 min. Diluted brain-heart infusion medium containing 25 mM PIPES buffer and 1.5 mM CaCl₂ was pulsed as the alternative growth medium. Specimens with intact biofilms were taken out on days 5, 12 and 20. The model was assessed by viable counts of the biofilm, mineral loss and lesion depth in the dentin specimens (by transversal microradiography) and pH measurements in the groove (by pH microelectrode). The results showed that biofilms formed on the dentin surface specimens were constant in viable counts for the low SPF, while this parameter tended to increase with time under the high SPF. Lesions with intact surfaces were formed and the lesion size increased significantly over time and increased significantly with increasing SPF. Typical Stephan curves were found after sucrose pulsing. The pH inside the groove returned to neutral under low SPF, but remained below 6.5 under high SPF. With the CDFF S. mutans biofilm model, lesions can be created in dentin within reasonable experimental time periods, as a result of the presence of a biofilm and in response to carbohydrate challenges.

Microbial composition and structure of a multispecies biofilm from a trickle‐bed reactor used for the removal of volatile aromatic hydrocarbons from a waste gas

AbstractThe microbial composition and structure of a multispecies biofilm of a laboratory‐scale trickle‐bed bioreactor for the treatment of waste gas was examined. The model pollutant was a volatile organic compound‐mixture of polyalkylated benzenes called Solvesso 100®. Fluorescent in‐situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) were applied. Two new Solvesso 100®‐degrading Pseudomonas sp strains were isolated from the multispecies biofilm. Corresponding isolate‐specific oligonucleotide probes were designed and applied successfully. A major finding was that the fraction of Solvesso 100®‐degrading bacteria in the biofilm was low (about 3–6% during long‐term operation). The majority of the active cells were saprophytes which utilized intermediates and cell lysis products. The measured fraction of extracellular polymeric substances of the mature biofilm was 89–93% of the total biomass. The CLSM examinations of a 3‐days‐old approx 10 µm thick biofilm revealed highly heterogeneous structures with distinguished three‐dimensional matrix‐enclosed microcolony bodies spread across the substratum surface. The 28‐days‐old 80–960 µm thick biofilm exhibited voids, cell‐free channels, and pores of variable sizes. In both cases, an even distribution of active cells and pollutant‐degrading bacteria throughout the biofilm cross‐section as well as through the biofilm depth was observed. Copyright © 2003 Society of Chemical Industry

The dependence of quorum sensing on the depth of a growing biofilm

In a process called quorum sensing, bacteria monitor their population density via extracellular signaling molecules and modulate gene expression accordingly. In this paper, a one-dimensional model of a growing Pseudomonas aeruginosa biofilm is examined. Quorum sensing has been included in the model through equations describing the production, degradation, and diffusion of the signaling molecules, acyl-homoserine lactones, in the biofilm. From this model, we are able to make some important observations about quorum sensing. First, in order for quorum sensing to initiate near the substratum, in accordance with experimental observations, the model suggests that cells in oxygen-deficient regions of the biofilm must still be synthesizing the signal compound. Second, the induction of quorum sensing is related to a critical biofilm depth; once the biofilm grows to the critical depth, quorum sensing is induced. Third, the critical biofilm depth varies with the pH of the surrounding fluid. Of particular interest is the prediction of a critical pH threshold, above which quorum sensing is not possible at any depth. These results highlight the importance of careful study of the relationship among metabolic activity of the bacterium, signal synthesis, and the chemistry of the surrounding environment.

Mass transport of macromolecules within an in vitro model of supragingival plaque.

The aim of this study was to examine the diffusion of macromolecules through an in vitro biofilm model of supragingival plaque. Polyspecies biofilms containing Actinomyces naeslundii, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus sobrinus, Veillonella dispar, and Candida albicans were formed on sintered hydroxyapatite disks and then incubated at room temperature for defined periods with fluorescent markers with molecular weights ranging from 3,000 to 900,000. Subsequent examination by confocal laser scanning microscopy revealed that the mean square penetration depths for all tested macromolecules except immunoglobulin M increased linearly with time, diffusion coefficients being linearly proportional to the cube roots of the molecular weights of the probes (range, 10,000 to 240,000). Compared to diffusion in bulk water, diffusion in the biofilms was markedly slower. The rate of diffusion for each probe appeared to be constant and not a function of biofilm depth. Analysis of diffusion phenomena through the biofilms suggested tortuosity as the most probable explanation for retarded diffusion. Selective binding of probes to receptors present in the biofilms could not explain the observed extent of retardation of diffusion. These results are relevant to oral health, as selective attenuated diffusion of fermentable carbohydrates and acids produced within dental plaque is thought to be essential for the development of carious lesions.

Sensitivity analysis of a biofilm model describing a one-stage completely autotrophic nitrogen removal (CANON) process.

A mathematical model for nitrification and anaerobic ammonium oxidation (ANAMMOX) processes in a single biofilm reactor (CANON) was developed. This model describes completely autotrophic conversion of ammonium to dinitrogen gas. Aerobic ammonium and nitrite oxidation were modeled together with ANAMMOX. The sensitivity of kinetic constants and biofilm and process parameters to the process performance was evaluated, and the total effluent concentrations were, in general, found to be insensitive to affinity constants. Increasing the amount of biomass by either increasing biofilm thickness and density or decreasing porosity had no significant influence on the total effluent concentrations, provided that a minimum total biomass was present in the reactor. The ANAMMOX process always occurred in the depth of the biofilm provided that the oxygen concentration was limiting. The optimal dissolved oxygen concentration level at which the maximum nitrogen removal occurred is related to a certain ammonium surface load on the biofilm. An ammonium surface load of 2 g N/m2. d, associated with a dissolved oxygen concentration level of 1.3 g O2/m3 in the bulk liquid and with a minimum biofilm depth of 1 mm seems a proper design condition for the one-stage ammonium removal process. Under this condition, the ammonium removal efficiency is 94% (82% for the total nitrogen removal efficiency) (30 degrees C). Better ammonium removal could be achieved with an increase in the dissolved oxygen concentration level, but this would strongly limit the ANAMMOX process and decrease total nitrogen removal. It can be concluded that a one-stage process is probably not optimal if a good nitrogen effluent is required. A two-stage process like the combined SHARON and ANAMMOX process would be advised for complete nitrogen removal.

Colonization of aerobic biofilms by sulfate‐reducing bacteria

The ability of the SRB Desulfovibrio desulfuricans to colonize aerobic heterotrophic or nitrifying biofilms on stainless steel surfaces was investigated by fluorescence in situ hybridization (FISH) in combination with confocal laser scanning microscopy (CLSM), the polymerase chain reaction (PCR) directed to the dissimilatory sulfite reductase and by oxygen microelectrodes. Biofilms of heterotrophic bacteria and of nitrifying bacteria pregrown on steel coupons in laboratory devices were not invaded by cells of D. desulfuricans within 1 week, even though large pores as possible entry paths and anoxic zones and sulfate in the medium as prerequisites for activity of D. desulfuricans existed in the biofilms. On the contrary, coinoculation of D. desulfuricans and aerobic heterotrophic bacteria from water of a cooling water system led to immediate establishment of a small but detectable population of D. desulfuricans distributed over the whole biofilm depth. The fact that individual SRB attached efficiently and irreversibly to steel suggests that in coinoculation experiments, establishment of SRB in the biofilm possibly occurred from the biofilm base, which is the zone that became anoxic first. Based on these findings it is suggested that the idea of protecting surfaces from SRB‐induced corrosion by pregrowing and maintaining specific bacterial biofilms should be further pursued.

Spatial Distribution of Extracellular Polymeric Substances in Biofilms

This study investigated the spatial distribution of biofilm extracellular polymeric substances (EPS) with depth in biofilms. Heterotrophic biofilms were grown in a rotating drum biofilm reactor fed with synthetic wastewater with a COD of 150 mg/L. Biofilm was found to be heterogeneously structured, represented not only by the spatial distribution of EPS yields but also by clearly defined aerobic/anoxic zones, increased density, decreased porosity, decreased soluble COD concentrations, and decreased viable biomass concentrations along the biofilm depth. Thicker biofilms exhibited greater soluble COD concentrations, EPS yields, and viable biomass than thinner biofilms. The net EPS yields in the biofilms are proportionally related to the amount of viable biomass present, and viable biomass loses its ability to produce EPS at the deeper sections because of its lower microbial activity resulting from lower nutrient availability. Also, it is possible that the naturally produced EPS was consumed as a substrate in the deeper layers, where more readily degradable organics were absent. The results of the spatial distribution of EPS yields gained in this paper provide helpful information to achieve a more complete description of heterogeneous biofilm structure. New biofilm models need to be developed to incorporate the EPS information to accurately reflect the heterogeneity of biofilms.

Functional and Structural Responses of a Degradative Microbial Community to Substrates with Varying Degrees of Complexity in Chemical Structure.

Abstract The objective of the present study was to determine whether cultivation of a degradative community on substrates with varying degrees of chlorination and complexity in chemical structure, as well as cultivation in batch and flow cell culture, would alter the community's functional capability. The community was isolated from oil-contaminated soil and maintained in the laboratory on 2,4,6-trichlorobenzoic acid for 5 months before its ability to grow on 15 different chemicals as sole carbon source was evaluated in batch and flow cell systems. While the community could grow and develop biofilms in flow cells on all the substrates, only 11 of the 15 substrates could support growth in batch culture. Although biofilm development was less extensive on chemicals such as pentachlorophenol (2.09% average area covered by biofilm; average biofilm depth = 3 µm) than on 2,4,6-trichlorobenzoic acid (50.84% area covered; biofilm depth = 6.4 µm), no correlation was observed between the degree of chlorination, or number of rings, and the number of planktonic cells or biofilm biomass. In contrast, physicochemical characteristics such as the octanol/water partition coefficient had a significant effect on the development of biofilm biomass. In the case of planktonic communities, the degree of chlorination and ring number also had no effect on the BIOLOG carbon utilization profiles of the resulting communities. Although the sessile communities generally clustered separately from their planktonic counterparts, principal component analysis of carbon utilization profiles of the sessile communities showed different grouping between growth on chlorinated and nonchlorinated substrates. Analysis of the degradative community maintained on 2,4,6-trichlorobenzoic acid over an extended period further showed that adaptation to a new chemical environment is a rather slow process, since the substrate utilization profiles did not stabilize even after 12 months. These results demonstrate the flexibility in metabolic ability and community structure found in microbial communities.http://link.springer-ny.com/link/service/journals/00248/bibs/38n3p215.html</hea

A microelectrode study of redox potential change in biofilms

In this study, we examined the stratification of microbial processes and the associated redox potential changes in biofilms using microelectrode techniques. Two types of biofilms, each with a different combination of microbial processes, were examined. The first type carried aerobic oxidation and sulfate reduction, while the second one provided aerobic oxidation and nitrification. The microelectrodes used were oxygen, sulfide, ammonium, pH and redox potential microelectrodes. The results of this study provide the following new experimental evidence: (1) The aerobic/sulfate-reducing biofilm had a clearly stratified structure with depth. In this biofilm, aerobic oxidation took place only in a shallow layer near the surface and sulfate reduction occurred in the deeper anoxic zone. The boundary between these two processes was well defined. (2) The aerobic/nitrifying biofilm also had a stratified structure with depth. In this biofilm, though aerobic oxidation took place throughout the biofilm depth, more nitrification occurred in the deeper section of the biofilm. The boundary between these two processes, however, was less well defined. (3) Redox potential could be an indicator for the existence of certain microbial processes in biofilms. The redox potential profile changes were correlated to shifts of microbial processes in both types of biofilms. The redox potential profiles in these biofilms can be used to elucidate the stratification of microbial processes in the biofilms.

Monitoring sulfate-reducing bacteria in heterotrophic biofilms

To a laboratory reactor, in which heterotrophic biofilms were grown on stainless steel coupons under aerobic conditions, sulfate-reducing bacteria (SRB) were added in order to elucidate whether and how these microorganisms were going to establish themselves in the biofilm. Polymerase chain reaction for the dissimilatory sulfite reductase gene and in situ hybridization with probes directed against 16S ribosomal RNA were used to detect the SRB in the biofilm. Both methods proved to be suitable tools for monitoring the SRB in these experiments, which lasted seven days. In a first series of experiments, in which the SRB were added after a biofilm had already developed, the SRB could be detected only one day after addition. No evidence was found that the SRB penetrated the biofilm and established themselves in the anaerobic niches which were present. In a second series of experiments, in which the SRB were inoculated together with a seed of aerobic heterotrophic microorganisms, the SRB were present in the biofilm over the whole biofilm depth and for the duration of the experiment. The study suggests that colonization of the steel coupons by the SRB added to the bulk fluid is hampered by the already developed biofilm, even though the heterogeneous biofilm structure and anaerobic zones in the biofilm depth offer the possibility for the SRB to penetrate and establish themselves.

Monitoring sulfate-reducing bacteria in heterotrophic biofilms

To a laboratory reactor, in which heterotrophic biofilms were grown on stainless steel coupons under aerobic conditions, sulfate-reducing bacteria (SRB) were added in order to elucidate whether and how these microorganisms were going to establish themselves in the biofilm. Polymerase chain reaction for the dissimilatory sulfite reductase gene and in situ hybridization with probes directed against 16S ribosomal RNA were used to detect the SRB in the biofilm. Both methods proved to be suitable tools for monitoring the SRB in these experiments, which lasted seven days. In a first series of experiments, in which the SRB were added after a biofilm had already developed, the SRB could be detected only one day after addition. No evidence was found that the SRB penetrated the biofilm and established themselves in the anaerobic niches which were present. In a second series of experiments, in which the SRB were inoculated together with a seed of aerobic heterotrophtc microorganisms, the SRB were present in the biofilm over the whole biofilm depth and for the duration of the experiment. The study suggests that colonization of the steel coupons by the SRB added to the bulk fluid is hampered by the already developed biofilm, even though the heterogeneous biofilm structure and anaerobic zones in the biofilm depth offer the possibility for the SRB to penetrate and establish themselves.

A microelectrode study of redox potential change in biofilms

In this study, we examined the stratification of microbial processes and the associated redox potential changes in biofilms using microelectrode techniques. Two types of biofilms, each with a different combination of microbial processes, were examined. The first type carried aerobic oxidation and sulfate reduction, while the second one provided aerobic oxidation and nitrification. The microelectrodes used were oxygen, sulfide, ammonium, pH and redox potential microelectrodes. The results of this study provide the following new experimental evidence: (1) The aerobic/sulfate-reducing biofilm had a clearly stratified structure with depth. In this biofilm, aerobic oxidation took place only to a shallow layer near the surface and sulfate reduction occurred in the deeper anoxic zone. The boundary between these two processes was well defined. (2) The aerobic/nitrifying biofilm also had a stratified structure with depth. In this biofilm, though aerobic oxidation took place throughout the biofilm depth, more nitrification occurred in the deeper section of the biofilm. The boundary between these two processes, however, was less well defined. (3) Redox potential could bean indicator for the existence of certain microbial processes in biofilms. The redox potential profile changes were correlated to shifts of microbial processes in both types of biofilms. The redox potential profiles in these biofilms can be used to elucidate the stratification of microbial processes in the biofilms

Application of multiple parameter imaging for the quantification of algal, bacterial and exopolymer components of microbial biofilms

Techniques are required for the simultaneous or sequential determination of multiple parameters within microbial biofilms. Confocal scanning laser microscopy in combination with a range of fluorescent probes and markers offers an approach to quantitatively defining many aspects of biofilm communities. By applying multispectral imaging in conjunction with nucleic acid stains, fluor conjugated lectins, and autofluorescence we have developed a simple approach to evaluate biofilm community composition. Biofilms were treated with the fluorescent nucleic acid stain SYTO 9 to allow quantification of bacterial biomass and fluor conjugated lectins (i.e., Triticum vulgaris lectin) to identify and allow quantification of exopolymeric substances. Far red autofluorescence was imaged to quantify algal biomass. Digital image analysis of the CSLM optical thin sections in each of the channels was used to determine such parameters as biofilm depth, bacterial cell area (biomass), exopolymer area and algal biomass at various depths and locations. In addition, three colour red–green–blue projections of the biofilms were computed. The method proved simple and effective for determining treatment effects such as grazing by invertebrates.

Spatial patterns of alkaline phosphatase expression within bacterial colonies and biofilms in response to phosphate starvation.

The expression of alkaline phosphatase in response to phosphate starvation was shown to be spatially and temporally heterogeneous in bacterial biofilms and colonies. A commercial alkaline phosphatase substrate that generates a fluorescent, insoluble product was used in conjunction with frozen sectioning techniques to visualize spatial patterns of enzyme expression in both Klebsiella pneumoniae and Pseudomonas aeruginosa biofilms. Some of the expression patterns observed revealed alkaline phosphatase activity at the boundary of the biofilm opposite the place where the staining substrate was delivered, indicating that the enzyme substrate penetrated the biofilm fully. Alkaline phosphatase accumulated linearly with time in K. pneumoniae colonies transferred from high-phosphate medium to low-phosphate medium up to specific activities of 50 mumol per min per mg of protein after 24 h. In K. pneumoniae biofilms and colonies, alkaline phosphatase was initially expressed in the region of the biofilm immediately adjacent to the carbon and energy source (glucose). In time, the region of alkaline phosphatase expression expanded inward until it spanned most, but not all, of the biofilm or colony depth. In contrast, expression of alkaline phosphatase in P. aeruginosa biofilms occurred in a thin, sharply delineated band at the biofilm-bulk fluid interface. In this case, the band of activity never occupied more than approximately one-sixth of the biofilm. These results are consistent with the working hypothesis that alkaline phosphatase expression patterns are primarily controlled by the local availability of either the carbon and energy source or the electron acceptor.

Measurement of polysaccharides and proteins in biofilm extracellular polymers

The structure of biofilm extracellular polymers (ECPs) was studied by measuring their polysaccharide and protein spatial distributions along biofilm depth. Biofilm was collected from two aerobic heterotrophic biofilm reactors, which were seeded with Sphingomonas sp. and Sphingomonas sp. plus mixed liquor, respectively, and operated under toxic organic (in this case, azo dye) degrading conditions. Complete mixing conditions in the two reactors were verified by measuring water content, and polysaccharide and protein quantities from three vertical sampling positions over time. Experimental results showed that: (1) the biofilm water content of either reactor did not change with sample position or biofilm age, with an average biofilm water content in both reactors of 97%; (2) polysaccharides and proteins in the ECPs did not change with sample position; (3) the profiles of polysaccharides and proteins along the biofilm depth showed a stratified biofilm structure, with their ratio (proteins/polysaccharides) being relatively stable over the depth. Oxygen and substrate transport and interactions among species were considered to be the main reasons for producing such a non-uniform biofilm structure; and (4) Sphingomonas sp. could not compete well with microorganisms derived from the mixed liquor of a wastewater treatment plant aeration basin.

Measurement of polysaccharides and proteins in biofilm extracellular polymers

The structure of biofilm extracellular polymers (ECPs) was studied by measuring their polysaccharide and protein spatial distributions along biofilm depth. Biofilm was collected from two aerobic heterotrophic biofilm reactors, which were seeded with Sphingomonas sp. and Sphingomonas sp. plus mixed liquor, respectively, and operated under toxic organic (in this case, azo dye) degrading conditions. Complete mixing conditions in the tworeactors were verified by measuring water content, and polysaccharide and protein quantities from three vertical sampling positions over time. Experimental results showed that: (1) the biofilm water content of either reactor did not change with sample position or biofilm age, with an average biofilm water content m both reactors of 97%; (2) polysaccharides and proteins in the ECPs did not change with sample position; (3) the profiles of polysaccharides and proteins along the biofilm depth showed a stratified biofilm structure, with their ratio (proteins/polysaccharides) being relatively stable over the depth. Oxygen and substrate transport and interactions among species were considered to be the main reasons for producing such a non-uniform biofilm structure; and (4) Sphingomonas sp. could not compete well with microorganisms derived from the mixed liquor of a wastewater treatment plant aeration basin.