Maximum Biofilm Thickness Research Articles

Modeling of oleaginous fungal biofilm developed on semi-solid media

An oleaginous fungus, Mortierella isabellina, able to transform efficiently sugar to storage lipid, was used as a model microorganism which develops a biofilm structure during the semi-solid fermentation process for the production of biodiesel from sweet sorghum. A mathematical model was developed to describe the fungal oil production in M. isabellina biofilm. The model describes diffusion and consumption of sugars and nitrogen of sweet sorghum and single cell oil production in a biofilm, which grows according to the kinetics of double-substrate limitation (sugars and nitrogen) with sugar inhibition. Experimental data from a previous experimental study were used to determine the kinetic parameters of the model. Maximum biofilm thickness and the percentage of lipid inside the biofilm were estimated using the model at 1892μm and 15%, respectively. The proposed mathematical model could prove a useful tool for designing semi-solid fermentation processes.

Acoustic and electrical property changes due to microbial growth and biofilm formation in porous media

A laboratory study was conducted to investigate the effect of microbial growth and biofilm formation on compressional waves, and complex conductivity during stimulated microbial growth. Over the 29 day duration of the experiment, compressional wave amplitudes and arrival times for the control (nonbiostimulated) sample were observed to be relatively uniform over the scanned 2‐D region. However, the biostimulated sample exhibited a high degree of spatial variability in both the amplitude and arrival times, with portions of the sample exhibiting increased attenuation (∼80%) concurrent with an increase in the arrival times, while other portions exhibited decreased attenuation (∼45%) and decreased arrival times. The acoustic amplitude and arrival times changed significantly in the biostimulated column between days 5 and 7 of the experiment, consistent with a peak in the imaginary conductivity (σ″) values. The σ″ response is interpreted as recording the different stages of biofilm development with peak σ″ representing maximum biofilm thickness and decreasing σ″ representing cell death or detachment. Environmental scanning electron microscope imaging confirmed microbial cell attachment to sand surfaces and showed apparent differences in the morphology of attached biomass between regions of increased and decreased attenuation. The heterogeneity in the elastic properties arises from the differences in the morphology and structure of attached biofilms. These results suggest that combining acoustic imaging and complex conductivity techniques can provide a powerful tool for assessing microbial growth or biofilm formation and the associated changes in porous media, such as those that occur during bioremediation and microbial enhanced oil recovery.

Nitritation performance and biofilm development of co- and counter-diffusion biofilm reactors: Modeling and experimental comparison

A comparative study was conducted on the start-up performance and biofilm development in two different biofilm reactors with aim of obtaining partial nitritation. The reactors were both operated under oxygen limited conditions, but differed in geometry. While substrates (O 2, NH 3) co-diffused in one geometry, they counter-diffused in the other. Mathematical simulations of these two geometries were implemented in two 1-D multispecies biofilm models using the AQUASIM software. Sensitivity analysis results showed that the oxygen mass transfer coefficient ( K i) and maximum specific growth rate of ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB) were the determinant parameters in nitrogen conversion simulations. The modeling simulations demonstrated that K i had stronger effects on nitrogen conversion at lower (0–10 m d −1) than at the higher values (>10 m d −1). The experimental results showed that the counter-diffusion biofilms developed faster and attained a larger maximum biofilm thickness than the co-diffusion biofilms. Under oxygen limited condition (DO < 0.1 mg L −1) and high pH (8.0–8.3), nitrite accumulation was triggered more significantly in co-diffusion than counter-diffusion biofilms by increasing the applied ammonia loading from 0.21 to 0.78 g NH 4 +-N L −1 d −1. The co- and counter-diffusion biofilms displayed very different spatial structures and population distributions after 120 days of operation. AOB were dominant throughout the biofilm depth in co-diffusion biofilms, while the counter-diffusion biofilms presented a stratified structure with an abundance of AOB and NOB at the base and putative heterotrophs at the surface of the biofilm, respectively.

Toward an operational dynamic model for tertiary nitrification by submerged biofiltration

This work deals with the methodology put in place to fit and validate the parameters of a biofiltration model (BAF) in tertiary nitrification treatment and dynamic conditions. For an average loading rate of 0.65 kg NH4-N/m(3) media/d, different time loading rates are applied inside a filtration-backwash run using a semi-industrial pilot. Comparisons between predicted and observed values on the NH4-N, NO3-N and TSS in treated water and the total head loss deltaP are carried out firstly using default values of BAF parameters. Model predictions overestimate values measured but trends are well reproduced. A sensitivity analysis is carried out and the hierarchy of BAF parameters has been set up classifying them into strong and low influence on the effluent concentrations. Among parameters revealing the strongest influence are those of the filtration module and the mean density of biofilm for the TSS effluent and the total AP, the specific autotrophic growth rate, the maximum biofilm thickness and the reduction coefficient of diffusivity in the biofilm for the NH4-N, NO3-N effluent. Finally, this classification leads to setting a calibration procedure, thanks to specific experimental tests directly measuring some BAF parameters.

Enhanced high copy number plasmid maintenance and heterologous protein production in an Escherichia coli biofilm

Escherichia coli has been widely used for heterologous protein production (HPP). To determine whether a biofilm environment could benefit E. coli HPP using high copy number plasmids, we compared plasmid maintenance and HPP by E. coli ATCC 33456 containing plasmid pEGFP (a pUC family vector) cultivated in biofilms and in suspended culture. Cells were grown with or without antibiotic selective pressure in flow cells or chemostats for up to 6 days. In biofilms, antibiotic selective pressure increased the plasmid copy number (PCN), but by 144 h, biofilms grown in antibiotic-free media had comparable plasmid concentrations. In the chemostat, the PCN declined steadily, although 100 ppm ampicillin in the medium slowed the rate of plasmid loss. Production of green fluorescent protein (GFP), a representative heterologous protein, was quantified by flow cytometry. In biofilms, at ampicillin concentrations >or=33 ppm, strongly fluorescent cells comprised more than half of the population by 48 h. In the chemostat, more than 50% of the population was non-fluorescent by 48 h in media containing 100 ppm ampicillin, and strongly fluorescent cells were <10% of the population. Biofilm structure was determined by confocal microscopy. Maximum biofilm thickness ranged from 30 to 45 microns, with no significant changes in biofilm structure after 48 h. Plasmid multimer percentages were similar to inocula for cells cultivated in either biofilms or the chemostat. The results indicate that the biofilm environment enhanced both plasmid maintenance and cellular GFP concentrations, and that low levels of antibiotic increased the beneficial effect.

Biofilm development in a membrane-aerated biofilm reactor: Effect of flow velocity on performance

The effect of liquid flow velocity on biofilm development in a membrane-aerated biofilm reactor was investigated both by mathematical modeling and by experiment, using Vibrio natriegens as a test organism and acetate as carbon substrate. It was shown that velocity influenced mass transfer in the diffusion boundary layer, the biomass detachment rate from the biofilm, and the maximum biofilm thickness attained. Values of the overall mass transfer coefficient of a tracer through the diffusion boundary layer, the biofilm, and the membrane were shown to be identical during different experiments at the maximum biofilm thickness. Comparison of the results with published values of this parameter in membrane attached biofilms showed a similar trend. Therefore, it was postulated that this result might indicate the mechanism that determines the maximum biofilm thickness in membrane attached biofilms. In a series of experiments, where conditions were set so that the active layer of the membrane attached biofilm was located close to the membrane biofilm interface, it was shown that the most critical effect on process performance was the effect of velocity on biofilm structure. Biofilm thickness and effective diffusivity influenced reaction and diffusion in a complex manner such that the yield of biomass on acetate was highly variable. Consideration of endogenous respiration in the mathematical model was validated by direct experimental measurements of yield coefficients. Good agreement between experimental measurements of acetate and oxygen uptake rates and their prediction by the mathematical model was achieved.

Ecotoxicological Assessment and Effects of Physicochemical Factors on Biofilm Development in Groundwater Conditions

A new concept in groundwater containment is the development of a biobarrier formed by the biostimulation of a microbial population and exopolysaccharides (EPS) production. Although the efficiency of biofilms to clog porous media and biotransform contaminants suggests their ap plication in aquifers, work on groundwater conditions has to be performed to confirm the potential of this technology. To determine the feasibility and the ecotoxic potential of biobarrier development, a groundwater indigenous population was inoculated in semicontinuous reactors. The effects of aeration, carbon source, feeding rate, C:N:P ratio, calcium ions, and pentachlorophenol (PCP) on biomass, EPS, and biofilm production was studied by a statistical design. The ecotoxic effect of soluble microbial products (SMPs) was assessed using two biotests: the Selenastrum capricornutum and Microtox (Vibrio fischeri) tests. Results showed that the carbon source type and its feeding rate had a significant impact on biofilm development leading to a maximum biofilm thickness of 250 μm after only 144 h. The ecotoxicological assessment revealed that S. capricornutum growth inhibition reached 80% while 90% of V. fischeri bioluminescence was affected by the presence of SMPs. Also, a toxic response was induced by the presence of PCP. These results showed the potential use of an indigenous microbial population and suggested that the ecotoxic potential has to be taken into account for in situ biobarrier development.

EVIDENCE FOR DYNAMIC PHENOMENA IN RESIDUAL TRACHEAL TUBE BIOFILM

It has been proposed recently that a dynamic physical process occurring in the tracheal tube might account for the dissemination of bacteria and biofilm fragments into the lungs during mechanical ventilation, and the subsequent development of ventilator-associated pneumonia. In this study of tracheal tubes from consecutive adult intensive care patients, biofilms were detected radiographically in 45 of 50 tubes, and were found at the lower end of the tube more often than at the upper end (P < 0.005). In 37 of 50 tracheal tubes, the maximum biofilm thickness was equal to or greater than the 0.5 mm required for gas-liquid interaction in a tube with an i.d. of 8.5 mm. In 23 of 50 tubes, wave-like patterns were found. Five tubes had no biofilm inside the bevelled tip and another six showed evidence of biofilm loss for a greater distance from the tip. These observations suggest that the distribution of tracheal tube biofilm is caused at least in part by dynamic phenomena in the tracheal tube.

Penicillin production in an inverse fluidized bed bioreactor

The inverse fluidized bed bioreactor was adapted for the axenic culture of heterotrophic microorganisms. Penicillin V synthesized by Penicillium chrysogenum ATCC 28089 was used as a model system for secondary metabolite production. The biomass growth rate was controlled by the rate of nutrient addition while an eroder in the inner draft tube limited the maximum biofilm thickness. When a lactose-rich, mineral salts medium was added at a rate of 0.024 l·h −1, the maximum specific productivity was 5.79 × 10 −4g (Pen V)·g (biomass) −1· h −1.

Effects of biocide and nutrient availability on microbial contamination of surfaces in cooling‐water systems

AbstractThe results of an evaluation of the effects of different factors on formation, growth and removal of biological films are reported. Experiments have been performed both on laboratory equipment and a test system located on a cooling‐water system at an industrial site.The effects of temperature, nutrient availability and surface material of construction are discussed in relation to film formation. Experiments concerning continuous biocide treatment are assessed in relation to biofilm removal. A pure culture of Pseudomonas fluorescens was used to grow biological films in the laboratory under identical hydrodynamic conditions but at different temperatures. Drastic reductions in film thickness were noted at temperatures 5°C above and below the optimum temperature for growth of the organism. The effects of nutrient loading under similar hydrodynamic conditions have been studied in the laboratory. The maximum biofilm thickness was reduced by 55% when no air was present and by 80% when neither air nor nutrient were supplied. Biofilm growth at the industrial site was unexpectedly more pronounced on brass than mild steel. Examination of destruction of existing biofilms in the laboratory showed that at a concentration of 4 parts 10−‐6 free chlorine (sodium hypochlorite) the initial rate of film removal was four‐to‐six times higher than that at 2.5 parts 10−‐6 free chlorine. A higher velocity of sodium hypochlorite solution over the biofilm resulted in a higher rate of removal. The results are discussed in the light of published data in related tests.