Transport limitation of chlorine disinfection of Pseudomonas aeruginosa entrapped in alginate beads

An artificial biofilm system consisting of Pseudomonas aeruginosa entrapped in alginate and agarose beads was used to demonstrate transport limitation of the rate of disinfection of entrapped bacteria by chlorine. Alginate gel beads with or without entrapped bacteria consumed chlorine. The specific rate of chlorine consumption increased with increasing cell loading in the gel beads and decreased with increasing bead radius. The value of an observable modulus comparing the rates of reaction and diffusion ranged from less than 0.1 to 8 depending on the bead radius and cell density. The observable modulus was largest for large (3-mm-diameter) beads with high cell loading (1.8 x 10(9) cfu/cm(3)) and smallest for small beads (0.5 mm diameter) with no cells added. A chlorine microelectrode was used to measure chlorine concentration profiles in agarose beads (3.0 mm diameter). Chlorine fully penetrated cell-free agarose beads rapidly; the concentration of chlorine at the bead center reached 50% of the bulk concentration within approximately 10 min after immersion in chlorine solution. When alginate and bacteria were incorporated into an agarose bead, pronounced chlorine concentration gradients persisted within the gel bead. Chlorine did gradually penetrate the bead, but at a greatly retarded rate; the time to reach 50% of the bulk concentration at the bead center was approximately 46 h. The overall rate of disinfection of entrapped bacteria was strongly dependent on cell density and bead radius. Small beads with low initial cell loading (0.5 mm diameter, 1.1 x 10(7) cfu/cm(3)) experienced rapid killing; viable cells could not be detected (<1.6 x 10(5) cfu/cm(3)) after 15 min of treatment in 2.5 mg/L chlorine. In contrast, the number of viable cells in larger beads with a higher initial cell density (3.0 mm diameter, 2.2 x 10(9) cfu/cm(3)) decreased only about 20% after 6 h of treatment in the same solution. Spatially nonuniform killing of bacteria within the beads was demonstrated by measuring the transient release of viable cells during dissolution of the beads. Bacteria were killed preferentially near the bead surface. Experimental results were consistent with transport limitation of the penetration of chlorine into the artificial biofilm arising from a reaction-diffusion interaction. The methods reported here provide tools for diagnosing the mechanism of biofilm resistance to reactive antimicrobial agents in such applications as the treatment of drinking and cooling waters.

Determination of diffusion coefficients and diffusion characteristics for chlorferon and diethylthiophosphate in Ca-alginate gel beads

Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited.

Use and engineering aspects of immobilized cells in biotechnology

A short review of the research in the past two years (1990-1991) on immobilized whole cells, such as microbial, plant, and animal cells, is presented including a discussion from an engineering point of view. Recent works concerning the intraparticle mass transfer effect on immobilized microbial cells by the authors and their co-workers are also introduced. Finally, future prospects of the immobilized cell system will be discussed.

Mathematical model for evaluation of mass transfer limitations in phenol biodegradation by immobilized Pseudomonas putida

A mathematical model is proposed to analyze the mass transfer limitations in phenol biodegradation using Pseudomonas putida immobilized in calcium alginate. The model takes into account internal and external mass transfer limitations, substrate inhibition kinetics and the dependence of the effective diffusivity of phenol in alginate gel on cell concentration. The model is validated with the experimental data from batch fermentation. The effect of various operating conditions such as initial phenol concentration, initial cell loading, alginate gel loading on the biodegradation of phenol is experimentally demonstrated. Phenol degradation time is found to decrease initially and reach stationary value with increase in cell loading as well as gel loading. The model predicts these trends reasonably well and shows the presence of external mass transfer limitations. A new concept of effectiveness factor is introduced to analyze the overall performance of batch fermentation.

Enumeration and factors influencing the relative abundance of a denitrifier, Pseudomonas sp. JR12, entrapped in alginate beads

The relative abundance of the denitrifier, Pseudomonas sp. JR12, was examined in an alginate-based entrapment complex under non-sterile, denitrifying conditions. Immuno-labeling of the Pseudomonas inoculant followed by flow cytometry (FCM) was used for determination of the relative abundance of this bacterium under the various incubation conditions. Additional information on the relative abundance of the inoculant was obtained by a quantitative enzyme-linked immunosorbent assay (ELISA) and results obtained by FCM and ELISA were compared. Ambient nitrate levels controlled the successful, long-term proliferation of the inoculant. At low ambient nitrate levels, Pseudomonas sp. remained the dominant microorganism during incubation. Higher ambient nitrate concentrations, attained by either decreasing the inoculum size of Pseudomonas sp. or raising inlet nitrate concentrations of the medium supplied to the incubation vessels, resulted in a gradual shift toward other, nitrite-accumulating denitrifiers. Thus far, most studies on the use of entrapped microorganisms for bioremediation purposes have been conducted under controlled laboratory conditions. Based on this study, conducted under non-sterile laboratory conditions, it is concluded that in-situ bioremediation using entrapped target microorganisms is bound to fail without a proper understanding of the factors that cause the target microorganism to out-compete undesired microbial invaders. Furthermore, based on the close agreement between the two detection methods used, it is concluded that flow cytometry provides a rapid and accurate tool for the detection of the relative abundance of immuno-labeled target organisms in heterogeneous microbial populations.

Analysis and description of the evolution of alginate immobilised cells systems

Different immobilised cells models, including very simple ones, can be useful in the fitting of experimental results. However, goodness or the ability to extrapolate results needs to be in accordance with basic observations and these will also suggest models to be proposed. In this paper, observations of calcium alginate/bacteria systems are used to show the ability of basic models to fit classic observations, as well as how new observations, in this case from electronic microscopy, oblige us to think about more complex mechanisms and mathematical treatments. Nevertheless it is not only important to discuss the model type, but also the type of kinetics assumed in the interior of the beads, as well as the internal structure, the boundary conditions related to bead shredding and cell escape and finally, geometrical effects.

Distribution of Nitrosomonas europaea and Paracoccus denitrificans immobilized in tubular polymeric gel for nitrogen removal

To improve the cooperative removal of nitrogen by Nitrosomonas europaea and Paracoccus denitrificans, we controlled their distribution in a tubular gel. When ethanol was supplied inside the tubular gel as an electron donor, their distributions overlapped in the external region of the gel. By changing the electron donor from ethanol to gaseous hydrogen, the distribution of P. denitrificans shifted to the inside of the tube and was separated from that of N. europaea. The separation resulted in an increase of the oxidation rate of ammonia by 25%.

Analysis of cell growth kinetics and substrate diffusion in a polymer scaffold

The cultivation of cartilage cells (chondrocytes) in polymer scaffolds leads to implants that may potentially be used to repair damaged joint cartilage or for reconstructive surgery. For this technique to be medically applicable, the physical parameters that govern cell growth in a polymer scaffold must be understood. This understanding of cell behavior under in vitro conditions, where diffusion is the primary mode of transport of nutrients, may aid in the scale-up of the cartilage generation process. A mathematical model of chondrocyte generation and nutrient consumption is developed here to analyze the behavior of cell growth in a biodegradable polymer matrix for a series of different thickness polymers. Recent literature has implied that the diffusion of nutrients is a major factor that limits cell growth (Freed et al., 1994). In the present paper, a mathematical model is developed to directly relate the effects of increasing cell mass in the polymer matrix on the transport of nutrients. Reaction and diffusion of nutrients in the cell-polymer system are described using the fundamental species continuity equations and the volume averaging method. The volume averaging method is utilized to derive a single averaged nutrient continuity equation that includes the effective transport properties. This approach allows for the derivation of effective diffusion and rate coefficients as functions of the cell volume fraction. The cell volume fraction as a function of time is determined by solution of a material balance on cell mass. Growth functions including the Moser, a modified Contois, and an nth-order heterogeneous growth kinetic model are evaluated through a parameter analysis, and the results are compared to experimental data found in the literature. The results indicate that cellular functions in conjunction with mass transfer processes can account partially for the general trends in the cell growth behavior for various thickness polymers. The Contois growth function appeared to describe the data more accurately in terms of the lag period at early times and the long time limits. However, all kinetic growth functions required variations in the kinetic parameters to fully describe the effects of polymer thickness. This result implies that restricted diffusion of nutrients is not the sole factor limiting cell growth when the thickness of the polymer is changed. Therefore, further experimental data and model improvements are needed to accurately describe the cell growth process.

Dynamic modeling of meta- and para-nitrobenzoate metabolism by a mixed co-immobilized culture of comamonas spp. JS46 and JS47

A model describing the transient activity of a mixed immobilized culture of Comamonas spp. JS46 and JS47 growing on mixed substrates is presented. The transient periods considered are those following changes in the feed carbon source, which alternated between meta- and para-nitrobenzoate. The feed profile alternately starved one of the species in the mixed culture. The response of the system, as quantified by the reactor effluent substrate concentrations, is dictated by the activity of the biomass and the appropriate biochemical pathway. As detailed mechanistic pathway information is not available, respirometry has been used to characterize both facets of activity. Two parameters were introduced: Psi representing pathway activity and Gamma representing biomass activity; a detailed description of the analysis is included. The model is compared to experimental investigation of the system and describes the reactor response well. The agreement between model and experiment suggests the usefulness of oxygen kinetics as global measurements to describe complex systems when mechanistic detail is not available. Copyright 1998 John Wiley & Sons, Inc.

Diffusion and transfer of antibody proteins from a sugar-based hydrogel

Diffusion of antibody protein from hydrogel films and hydrogel encapsulated in a microcapillary was studied. Thin hydrogel films were formed by crosslinking 6-acryloyl-B-O-methylgalactoside with N,N'-methylene-bis-acrylamide and the diffusive transport of monoclonal antimouse IgG-FITC into and out of the hydrate films was measured. Diffusion coefficients in 2 and 4% crosslinked hydrogel films were measured. The measured diffusion constants determined for IgG in both the 2 and 4% hydrogel films were comparable to the free diffusion of IgG in bulk water (Dmean approximately 10(-7) cm2/s). In addition, 2% crosslinked hydrogels were prepared in a capillary tube and the transport of antimouse IgG-FITC into and out of the hydrated hydrogel was measured. Kinetic analysis indicated that the protein transport through the capillary hydrogel was faster than would be expected for a simple diffusion process. Finally, by utilizing the diffusion of antibody from the capillary hydrogel, transfer of antibody to a silica surface was demonstrated. A capillary hydrogel loaded with antimouse IgG-FITC was used to transfer the protein to a silica surface forming a 30-micron spot of antibody, which was imaged using fluorescence microscopy. These results may lead to the development of a nonlithographic method of patterning antibodies on surfaces for use in integrated microimmunosensors.

5-Fluorouracil release from copolymeric hydrogels of itaconic acid monoester. I. Acrylamide-co-monomethyl itaconate

The aim of this work was to test the application of new copolymeric poly (acrylamide-co-monomethyl itaconate) (A/MMI) hydrogels to 5-fluorouracil (5-FU) release. Three different compositions of copolymers have been studied, 90A:10MMI 75A:25MMI and 60A:40MMI. The equilibrium swelling degree in saline solution was between 76 and 80% depending on the copolymer composition. 5-FU, as the sodium salt, was trapped in the gels by including it in the feed mixture of polymerization. The swelling kinetics of the hydrogels in saline solution were studied at four temperatures, and the diffusion coefficient and the activation energy of the process were obtained. The 5-FU release as a function of temperature and disc load was studied; the diffusion coefficient and the activation energy of the release process were also obtained. The diffusion studies follow Fick's second law.

Nonuniform spatial patterns of respiratory activity within biofilms during disinfection

Fluorescent stains in conjunction with cryoembedding and image analysis were applied to demonstrate spatial gradients in respiratory activity within bacterial biofilms during disinfection with monochloramine. Biofilms of Klebsiella pneumoniae and Pseudomonas aeruginosa grown together on stainless steel surfaces in continuous-flow annular reactors were treated with 2 mg of monochloramine per liter (influent concentration) for 2 h. Relatively little biofilm removal occurred as evidenced by total cell direct counts. Plate counts (of both species summed) indicated an average 1.3-log decrease after exposure to 2 mg of monochloramine per liter. The fluorogenic redox indicator 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and the DNA stain 4',6-diamidino-2-phenylindole (DAPI) were used to differentiate respiring and nonrespiring cells in biofilms. Epifluorescence micrographs of frozen biofilm cross sections clearly revealed gradients of respiratory activity within biofilms in response to monochloramine treatment. These gradients in specific respiratory activity were quantified by calculating the ratio of CTC and DAPI intensities measured by image analysis. Cells near the biofilm-bulk fluid interface lost respiratory activity first. After 2 h of biocide treatment, greater respiratory activity persisted deep in the biofilm than near the biofilm-bulk fluid interface.

Cell growth patterns in immobilization matrices

Within an immobilized cell matrix, mass transfer limitations on substrate delivery or product removal can often lead to a wide range of local chemical environments. As immobilized living cell populations actively grow and adapt to their surroundings, these mass transfer effects often lead to strong, time-dependent spatial variations in substrate concentration and biomass densities and growth rates. This review focuses on the methods that have been devised, both experimentally and theoretically, to study the non-uniform growth patterns that arise in the mass transfer limited environment of an immobilization matrix, with particular attention being paid to cell growth in polysaccharide gels.

Immobilization of cells for application in the food industry

Immobilization of cells offers advantages to the food process industries, including enhanced fermentation productivity and cell stability and reduced downstream processing costs due to facilitated cell recovery and recycle. This article summarizes the varied immobilization methodologies, including adsorption, entrapment, covalent binding, and microencapsulation. Examples of interest to the food industry are provided, together with a review of the physiological effects of immobilization. Topics in process engineering include immobilized cell bioreactor configurations and the scale-up potential of the various immobilization techniques.