Charles D. Scott

Immobilized cells: a review of recent literature

Abstract Advanced biocatalytic systems using immobilized cells have potential utility in various bioprocessing schemes and for biomedical and analytical purposes. Important advances continue to be made in the techniques of immobilization, the characterization of the resulting biocatalyst and potential applications. This review examines the recent literature in the area of cellular immobilization; it covers applications ranging from wastewater treatment to the production of therapeutics. New immobilization materials, several different bioreactor concepts and the properties of many specific systems are discussed. Anticipated future research trends are also outlined.

Solute diffusion in biocatalyst gel beads containing biocatalysis and other additives

Abstract Biocatalyst beads can be produced by the entrapment of microorganisms or enzymes into a stabilized hydrocolloidal gel such as alginate or carrageenan. In order to determine and predict the effectiveness of such catalytic material, it will be necessary to know the mass transport properties of substrates and products within the gel beads, especially where there are high concentrations of the biocatalyst or other additives. Diffusion of several solutes within the beads has been studied by measuring the transport of solutes to and from a well-stirred solution of limited volume. Tests have been performed with biocatalyst beads made from alginate and carrageenan covering a range of bead diameter, gel concentration, concentration of biocatalyst and other additives, and solute molecular weight. At low gel concentration with entrapped biocatalyst, a solute of low molecular weight has a diffusion coefficient approaching that measured in water. However, with increased gel concentration, and especially with high loadings of microorganisms and other additives, the diffusion coefficients are significantly decreased. An empirical relationship was developed for the diffusion coefficient as a function of microbial loading.

Operability and feasibility of ethanol production by immobilizedZymomonas mobilis in a fluidized-bed bioreactor

Studies have been carried out using immobilized Z.mobilis in fluidized-bed bioreactors and have emphasized operation during high productivity and conversion. The bacteria are immobilized within small uniform beads (~1 to 1.5-mm diam) of K-carrageenan at cell loadings of 15-50 g (dry wt)/L. Conversion and productivity were measured under a variety of conditions, including feedstocks, flow rates, temperature, pH, and column sizes (up to 2.5 m tall). Volumetric productivities of 50-120 g EtOH/h-L reactor volume have been achieved. Productivities of 60 g/h-L are demonstrated from a 15% feed with residual glucose concentrations of less than 0.1% and 7.4% EtOH in the tallest fermentor. Among feeds of 10, 15, and 20% dextrose, the 15% gave the highest productivity and avoided substrate inhibition. A temperature of 30°C and pH 5 were the optimum conditions. The ethanol yield was shown to be nearly constant at 0.49 g EtOH/g glucose, or 97% of the theoretical under a variety of conditions and transients. The biocatalyst beads have been shown to remain active for two months. Nonsterile feed has been used for weeks without detrimental contamination. The advantages of this advanced bioreactor system over conventional batch technology are discussed.

Automatic, High-Resolution Analysis of Urine for Its Ultraviolet-Absorbing Constituents.∗

Over 300 compounds have been reported in human urine (1-4). These include inorganic compounds, organic acids, sugars, amino acids, purines and related compounds, enzymes, hormones, vitamins and their metabolites, estrogens, and many other organic compounds. The quantities of these constituents found in individual urine samples represent a wealth of information that can be used to evaluate body functions. Such quantitative data have been collected on a limited basis for many years and, as a result, many molecular constituents have been shown to have pathological significance. For example, a high uric acid content is associated with gout(5) and some leukemias (6); a high urocanic acid content is sometimes found in conjunction with asthma(7); large amounts of phenolic and indole amines appear to be excreted by schizophrenics(8), etc. The Molecular Anatomy (MAN) program at Oak Ridge National Laboratory(9) is concerned with the description, at the molecular level, of the structure and organization of cells and tissue. One of the aims of this program is to develop high-resolution, automated systems for the analysis of low-molecular-weight substances found either free in cells or as constituents of macro molecules. A logical extension of this work is the further development of such analytical systems for use with human body fluids. This laboratory is now developing an automatic, high resolution analytical system for quantitatively determining the molecular constituents of human urine. The approach is to modify and expand the capabilities of an existing nucleotide analyzer (10) for use as a urine analyzer. Initial results indicate that this concept is feasible; i.e., a high-pressure, high-resolution modification of the nucleotide analyzer has resolved over 100 chromatographic peaks of ultraviolet-absorbing constituents from a 2-ml urine sample. Twelve of these peaks have been tentatively identified.

Techniques for Producing Monodispersed Biocatalyst Beads for Use in Columnar Bioreactorsa

The use of columnar bioreactors such as fixed or fluidized beds requires that the biocatalyst (e.g., microorganism) be immobilized into or onto solid support materials that will not be swept out of the bioreactor a t the high flow rates frequently used in these systems. At the same time, the path length to and through the biocatalyst must be relatively short to reduce the effects of mass transport of substrates and products; thus, small particles or thin films of the biocatalyst should be used. In the case of fluidized-bed systems, the resulting particles must also be sufficiently small and dense to ensure fluidization without washout. If active microorganisms are used, immobilization can be carried out by interaction of the cell with a particulate surface or by encapsulation or entrapment of the organisms into a solid matrix such as a hydrocolloidal gel. The latter approach is of particular interest for systems where a well-defined microbial population is to be maintained, especially if system asepsis cannot be ensured. Many researchers have investigated the use of gel materials (e.g., calcium alginate and K-carrageenan) for microbial entrapment, usually with biocatalyst beads (2-5 mm diam.) that were prepared by dispersing droplets of the gel material from a pipette or needle into a cation-fixing solution.’4 Klein and Vorlop have demonstrated that the particle size of the droplets can be reduced by forced flow through a small nozzle, and Hulst et al. have shown that the imposition of “tuned”’ vibrational force into the droplet formation system can be used to form alginate particulates that are essentially monodispersed in the size range I to 2 mm diam.6 This approach has now been extended by using a somewhat simpler apparatus, based on previous work for a different application,’.’ to produce essentially monodispersed biocatalyst beads in the size range 0.5 to 3.0 mm diam. for gel materials such as alginate and K-carrageenan-a range encompassing particulates compatible with fluidized-bed operation. The surface properties and specific gravities of the beads can also be altered, as needed, to optimize the intended use. The obvious advantages of this material make it a prime candidate for application in high-productivity, fluidized-bed bioreactors such as those that may be used for the conversion of glucose to ethanol.

Coal solubilization by enhanced enzyme activity in organic solvents

Both oxidative and reductive enzymes can be utilized to enhance coal solubilization in aqueous and organic media. Aerobic solubilization was carried out with oxidases in a relatively polar medium, whereas solubilization in an anaerobic environment was conducted with reducing enzymes (dehydrogenase or hydrogenase) in aqueous and both polar and nonpolar organic media in the presence of hydrogen or a hydrogen donor. Solubilization of some enzymes in organic liquids was enhanced by complexation with polyethylene glycol. Enzyme concentration of 1–20 mg/mL was used, and most of the reactions occurred during the first 4 h, with up to 85% of the coal solubilized. There was some evidence of coal product inhibition and enzyme deactivation at higher temperatures.

An advanced bioprocessing concept for the conversion of waste paper to ethanol : scientific note

ConclusionsWaste paper is a plentiful and low-cost lignocellulosic feed material that may represent the most direct way to penetrate the market with an advanced bioprocessing system. Innovative bioprocessing concepts integrated into such a system for the production of ethanol should be economically viable. Several of the proposed processing advances for such a system have only been studied on a laboratory scale, so a more thorough process development and scale-up effort will be required.

Adsorption of Sr by immobilized microorganisms

Wastewaters from numerous industrial and laboratory operations can contain toxic or undesirable components such as metal ions, which must be removed before discharge to surface waters. Adsorption processes that have high removal efficiencies are attractive methods for removing such contaminants. For economic operations, it is desirable to have an adsorbent that is selective for the metal contaminant of interest, has high capacity for the contaminant, has rapid adsorption kinetics, can be economically produced, and can be regenerated to a concentrated waste product or decomposed to a low-volume waste. Selected microorganisms are potentially useful adsorbents for these applications because they can be inexpensive, have high selectivities, and have high capacities for adsorption of many heavy metals, which are often problems in a variety of industries.

Ethanol, the ultimate feedstock : a technoeconomic evaluation of ethanol manufacture in fluidized bed bioreactors operating with immobilized cells

Ethanol appears to be a key factor in the “biomass alternative” to fossil feedstocks for producing fuels and chemicals. If produced at a low enough price relative to crude oil, it and its derivates could account for 159 billion pounds, or 50%, of the US production of synthetic organic chemicals, presently valued at

Nonpulsing reagent metering for continuous colorimetric detection systems

113 billion. This use would consume 4.2 billion bushels, or about 54%, of the corn crop.This study evaluated the potential savings in ethanol manufacture to be gained by applying advanced process engineering or genetic engineering of improved organisms, centering on the use of fluidized bed bioreactors operating at high cell densities with immobilized cells of either the Saccharomyces yeast or the bacterium: Zymomonas mobilis.A new continuous plant could produce at about