Immobilization of microbial cells

Sodium chlorite oxidation of com and rice starches is recommended for the production of textile sizes (101) and oxidized starch is recommended as a hardening agent in the immobilization of microbial cells within gelatin (102). 

The immobilization of microbial cells under conditions where an activity or set of enzymic activities remains intact, but the normal metabolic processes cease, represents a novel technique for enzyme immobilization. Moreover, immobilized cells might enable the standard fermentation methods to be replaced by immobilized -cell -based continuous processes. 

A Freeman, Y Aharonowitz. Immobilization of microbial cells in crosslinked, polymerized linear polyacrylamide gels antibiotic production by immobilized Streptomyces clavuligerus cells. Biotechnol Bioeng 23 2747-2759, 1981. 

We attempted continuous production of L-aspartic acid from fumaric acid and ammonia by immobilized Escherichia coli having high aspartase activity [3, 4, 5]. Various methods were tested for the immobilization of microbial cells, and a stable and active enzyme system was obtained by entrapping whole microbial cells in a polyacrylamide gel lattice. 

Current applications of continuous enzyme reactions using immobilized microbial cells for the transformation of useful compounds are mainly carried out by the action of a single enzyme. However, many useful compounds are usually produced, especially in fermentative processes, by the action of several kinds of enzjmies. Only a few papers have been published on the immobilization of microbial cells operating in m.ulti-step enz)mie reactions, and little is known about the conditions for immobilization and the enz3miatic properties of the immobilized cells containing the multi-step system (, ). 

Facile Methods for the Immobilization of Microbial Cells without Disruption of their Life Processes... 

For further improvement of these immobilization systems, we investigated many sjmthetic and natural polymers as a matrix for entrapping enzymes and microbial cells into gel lattice. As a result, we [8, J] found that "K-carrageenan" is one of the most suitable polymer for Immobilization of microbial cells. 

In this paper, the immobilization of microbial cells with polyacrylamide gel and K-carrageenan, and their industrial application are reviewed. 

As described above, the polyacrylamide gel method is advantageous for Immobilization of microbial cells and for industrial application. However, there are some limitations in this method. That is, some enzymes are inactivated during Immobilization procedure by the action of acrylamide monomer, 8-dimethylamino-propionitril, potassium persulfate or heat of the polymerization reaction. Therefore, this method has limitation in application for immobilization of enzymes and microbial cells. Thus, to find out more general Immobilization technique and to Improve the productivities of Immobilized microbial cell systems we studied new immobilization techniques. As the results, we have found out K-carrageenan is very useful for Immobilization of cells [8]. <-Carrageenan, which is composed of unit structure of B-D-galactose... 

Since K-carrageenan was found to be a useful matrix for immobilization of microbial cells, we extensively studied this carrageenan method to improve the industrial production of L-aspartlc acid using immobilized E. CO-Li cells prepared by polyacrylamide gel method [18]. 

Polymeric materials play essential roles in the life sciences. The supermacroporous cryogels were first used for immobilization of microbial cells [1], but later found many new and exciting applications [2]. Their high porosity combined with very good biocompatibility, mechanical strength, and ease of preparation are reasons... 

An early development in the area of utilization of cryogels in biotechnology was immobilization of microbial cells in PVA gels that were produced via repeated freeze-thaw cycles [4]. The first reports indicated that high viability, good mass transfer, and mechanical stability were obtained. The gels were elastic and could therefore be used repeatedly. Table 1 lists some of the reports on cryogels with immobilized biocatalysts (microbial cells and/or enzymes). 

The immobilization of microbial cells, subcellular organelles, and enzymes in calcium alginate gels. Biotechnol. Bioeng., 19, 387-397. 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

Bubble columns in which gas is bubbled through suspensions of solid particles in liquids are known as slurry bubble columns . These are widely used as reactors for a variety of chemical reactions, and also as bioreactors with suspensions of microbial cells or particles of immobilized enzymes. 

Immobilization of whole microbial cells for industrial purposes eliminates the need for the isolation, purification and attachment of enzymes and provides the enzymes with a microenvironment maintained at optimal conditions by cellular metabolic and transport activities. Adhesion of microbial cells to inert substrata often occurs in nature and greater understanding of these natural processes may lead to advances in the technology of whole cell immobilization. Mechanisms of attachment in natural systems involve adhesive microexudates produced by the cells, electrostatic attraction, and anatomical projections which cling to the support surface. The chemical methods which have been used for whole cell immobilization have recently been reviewed by Jack and Zajic (1 ). 

These considerations lead to the conclusion that a rational approach to.problems of the adhesion of cells to solid surfaces can be developed from knowledge of the surface properties of both the substrate and the cell. Solid surface energies can be obtained by measurements of contact angles and use of Neumann s equation (Eq. 6), thus allowing calculations of free energy charges associated with adhesion. Zeta potentials and resultant electrostatic contributions to adhesion can also be obtained experimentally. This type of approach should provide insight into microbial adhesion problems in the marine and aquatic environments, disease and infection and in the industrial immobilization of whole cells. 

The immobilization of animal cells is still in its infancy. This is at least partly because of the fact that such cells are far more labile and sensitive than microbial cells and that most immobilization procedures hitherto used have been too drastic for the animal cells to survive. However, the biospecific interactions offered by glucoproteins on the cell surface and lectins on the support may be utilized for immobilization to take place (4,47, ). 

Conventional fermentative production of carbohydrates has received considerable attention, particularly with respect to the use of xanthan as an adjunct to oil-well drilling. Biochemists and chemists are becoming increasingly aware of the potential of immobilizing whole microbial cells for the large-scale production of a wide variety of molecules. 

Freeman A. and Lilly M.D. Effect of processing parameters on the feasibility and operational stability of immobilized viable microbial cells. Enzyme and Microbial Technology 23 (5) (1998) 335-345. 

Most studies on microbial exopolysaccharides production have been performed so far using batch fermentation conditions and polymer macromolecules are recovered from fermentation broths by simple chemical and physical techniques, e.g. precipitation and centrifugation. In Scheme 7.2 the route of production of alginate is presented [8]. Some attempts have been made to apply immobilized-cell cultures to the production of alginate and other bacterial polysaccharides. Immobilization techniques are likely to allow the permanent separation of microbial cells from the incubation broth. In the last few years, however, membrane processes have been increasingly used to separate microbial cells from the production medium. A number of studies have therefore focused on the microfiltration of fermentation broths after batch incubation and the mechanisms of membrane fouling by cells, debris, colloidal particles and macromolecules, e.g. for recovery of polysaccharides from fermentation broths [2]. 

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