Whole cell immobilization

D-Pantolactone and L-pantolactone are used as chiral intermediates in chemical synthesis, whereas pantoic acid is used as a vitamin B2 complex. All can be obtained from racemic mixtures by consecutive enzymatic hydrolysis and extraction. Subsequently, the desired hydrolysed enantiomer is lactonized, extracted and crystallized (Figure 4.6). The nondesired enantiomer is reracemized and recycled into the plug-flow reactor [33,34]. Herewith, a conversion of 90-95% is reached, meaning that the resolution of racemic mixtures is an alternative to a possible chiral synthesis. The applied y-lactonase from Fusarium oxysporum in the form of resting whole cells immobilized in calcium alginate beads retains more than 90% of its initial activity even after 180 days of continuous use. The biotransformation yielding D-pantolactone in a fixed-bed reactor skips several steps here that are necessary in the chemical resolution. Hence, the illustrated process carried out by Fuji Chemical Industries Co., Ltd is an elegant way for resolution of racemic mixtures. 

Whole cell immobilization was defined by Karel et al. [35] as, the physical confinement or localization of intact cells to a certain region of space with preservation of some desired catalytic activity or by Anderson [36] as, there is a physical confinement or localization of microorganisms that permits their economic... 

Enzymes can be immobilized by matrix entrapment, by microencapsulation, by physical or ionic adsorption, by covalent binding to organic or inorganic polymer-carriers, or by whole cell immobilization (5 ). Particularly impressive is the great number of chemical reactions developed for the covalent binding of enzymes to inorganic carriers such as glass, to natural polymers such as cellulose or Sepharose, and to synthetic polymers such as nylon, polyacrylamide, and other vinyl polymers and... 

Dual Hollow-Fiber Bioreactor for Aerobic Whole-Cell Immobilization... 

The overall rationale for whole cell immobilization is outlined in Table 3. 

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 ). 

Entrapment in polymeric networks is still the most widely used technique in whole cell immobilization. Such polymeric networks were originally prepared by precipitation — with-(j[) or without hardening — or crosslinking polymerization. ... 

The ionic network formation procedure was originally developed by Thiele and coworkers (11,12) and our laboratory was the first to adopt and modify thisTecFnique to be applicable for whole cell immobilization ( h It was our impression that the contact of the cells with polyelectrolytes and some small electrolytes in aqueous solution only would be most advantageous to maintain high fraction of enzymatic activity and living cells after immobilization. 

The Use of Whole Cell Immobilization for the Production of Glucose Isomerase... 

Various methods have been proposed for whole cell Immobilization Including adsorption and covalent attachment to a preformed carrier, crosslinking, flocculation, microencapsulation, and entrapment. Physical entrapment In a porous matrix Is by far the most flexible and most commonly used technique. Considering the fact that the polymer network has to be formed In the presence of the finally entrapped biological material, the performance criteria of chemical and physical nature are as follows ... 

The same methods are also used to immobilize whole cells. Immobilization of cells avoids the tedious isolation and puriHcation of enzymes. The activity of the immobilized cells can be reduced by toxicity during immobilization and by hindered diffusion of the substrate. But the immobilized cells may also be more active than the free cells as well, since complete or incomplete destruction of the cell walls removes certain proteases from the cell which would otherwise degrade and thereby deactivate enzymes. For example, E. coli bacteria encapsulated in poly(acrylamide) gels are used commercially to convert sodium fumarate to L-aspartic acid. 

Philp JC, Babnand S, Hajto E, Bailey MJ, Wibes S, Whiteley AS, Lilley AK, Hajto J, Dunbar S A (2003) Whole cell immobilized biosensors for toxicity assessment of a wastewater treatment plant treating phenolics-containing waste. Anal Chim Acta 487 61-74... 

For the continuous production of xylitol with high yields, techniques of whole cell immobilization and cell-recycle fermentation have been used. Candida tropicalis cells were immobilized into calcium alginate, polyacrylamide, a cylindrical porous ceramic, and a nonwoven polyester fabric. At a condition to minimize the loss of the immobilized yeast cells, 86.6 g/L xylitol was produced with a xylitol productivity of... 

There are many strategies for whole cell immobilization playing the biocatalyst role in the biorefinery processes. Suto and co-workers studied the... 

An enzyme membrane bioreactor can be created in different configurations the membrane can be used in order to confine or separate the biocatalyst from the reaction mixture furthermore, membranes can be used as a support for biocatalysts (enzymes or whole cells) immobilization. 

Biocatalysts can be immobilized using either the isolated enzymes or the whole cells. Immobilization of whole cells is an easier alternative to immobilization of isolated enzymes due to operational facility. But, at the same time, immobilized cells show lower catalytic activity compared with immobilized enzymes. 

By far the largest number of applications of polymeric materials in the field of biochemistry have been associated with enzyme and whole cell immobilization, affinity and covalent chromatography, and the immobilization of biologically-related reducing agents. 

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