Immobilization of cells

Among the wide choice of reactor designs, the biofilm reactor is one of the best suited for azo-dye conversion as it meets two important process requisites. The first is related to the hindered growth feature of bacterial metabolism under anaerobic conditions. The second is related to the necessity to increase cell densities (see previous section) with respect to those commonly harvested in liquid broths [55, 56]. Except for bacteria that forms aggregates spontaneously, immobilization of cells on granular carriers and membrane reactor technology are the two common pathways to achieve high-density confined cell cultures in either discontinuous or flow reactors. 

Numerous different immobilization methods have been reported that take advantage of various enzyme properties such as size, chemically reactive functionality, ionic groups or hydrophobic domains.Based on these properties, enzyme immobilization can be split into three main classes (which are also applicable to the immobilization of cell cultures) ... 

Lopez, S., Valero, F., and Sola, C., Immobilization of Cells Strategies in lipase production by immobilized Candida rugosa cells, Appl. Biochem. Biotechnol. 1996 vol. 59, no. 1, pp. 15-24. 

Subsurface environmental conditions are suboptimal with low temperatures and low concentrations of growth nutrients. The decline of bacterial inoculae by protozoan predation is of major concern in soil (Acea etal., 1988 Acea Alexander, 1988 Casida, 1989) but may not be a factor in saturated subsurface environments. Immobilization of cells to carrier material may enhance microbial survival in the environment through control of predation and supply of nutrients and moisture. Stormo Crawford (1992) developed a cell immobilization technique for production of small beads (2-50 /rm) consisting of agarose and cells of PCP-degrading Flavobacterium sp. Microencapsulated Flavobacteria efficiently degraded PCP and survived for two years in soil columns at environmental conditions (Stormo Crawford, 1994). These results show that microencapsulation may be a very useful tool in in situ bioremediation. 

Many alternative fermenters have been proposed and tested. These fermenters were designed to improve either the disadvantages of the stirred tank fermenter-high power consumption and shear damage, or to meet a specific requirement of a certain fermentation process, such as better aeration, effective heat removal, cell separation or retention, immobilization of cells, the reduction of equipment and operating costs for inexpensive bulk products, and unusually large designs. 

For bioprocessing purposes, increase in the stability of biocatalysts is quite often achieved by immobilization of cells or enzymes [57-60], This technology is an attractive alternative to the use of expensive free enzymes and cofactors, and can coordinate multistep enzymatic processes into a single operation. Furthermore, fermentative biosynthesis of cephamycin C using immobilized cells of S. clavuli-gerus NRRL 3585 was accomplished by Freeman and Aharonowitz [61], Jensen et al. [62] reported on the immobilization of P-lactam synthesizing enzymes from the same wild-type culture. None of these early studies used penicillin substrates other than the normal intermediate penicillin N, such as penicillin G. 

The aggregation of cells in suspension culture leads to a heterogeneous population that confound the analysis and operations of the reactor types mentioned above in many cases. For non-growth associated products, immobilization of cells provides a... 

While the composition and sequence of the amino acids have been known since 1983 (2,3), methods for increased-scale extraction were not developed until 1985. This scaled production has allowed for the development of single-part adhesive systems (Cell-Tak adhesive) for the immobilization of biologically active moieties to inert substrates. It has also permitted research on two-part adhesive formulations for the bonding of tissues. This paper specifically addresses the biocompatibility issue with descriptions of the immobilization of cells to Cell-Tak protein-coated plasticware, methods for wound closure, and preliminary toxicology data. 

The fixed-bed, porous-glass-sphere culture system was designed for the production of secreted cell products and lytic virus. The system is based on the immobilization of cells (anchorage-dependent or suspension) to high cell densities in porous glass spheres (supplied by Schott Glaswerke). 

For enhanced scaled-up cyclosporin production, a modified sporulation/immobili-zation method has been proposed, increasing the cyclosporin yield up to tenfold, compared to suspended culture techniques [106]. The immobilization of cells on celite carrier beads decreases the culture s viscosity and therefore increases the mass transfer. It is possible to run the fermentation continuously since the fungal spores can be trapped in the fermenter vessel to populate and germinate on freshly added beads. 

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... 

Enzymatic processes are important in the areas of erop protection and pharma intermediates too. Technical improvements can result directly from immobilization (e. g. increased product purity and/or yield, reduced waste production) but also indirectly. Immobilization of cells or enzymes enables the use of eontinuous rather than batch operation, thus simplifying process control and reducing labor costs. Of course, this is only advantageous for large-scale processes, whereas most bioproducts are only produced on a small scale. 

Conditions for the gelation of k-carrageenan, a new matrix for the immobilization of cells and enzymes, have been investigated and a number of cells and enzymes successfully immobilized. Operational stability was found to be enhanced by hardening with glutaraldehyde or 1,6-diaminohexane. Brevi-bacterium flavum cells have also been immobilized by gelation in K-carra-geenan. ... 

Immobilization of Cells. — The immobilization of cellular material for use both in affinity chromatography and for the production of enzymatically active preparations continues to receive considerable attention, as has been described... 

V. Manojlovic, J. Djonlagic, B. Obradovic, V. Nedovic, and B. Bugarski. Immobilization of cells by electrostatic droplet generation A model system for potential application in medicine. International Journal of Nanomedicine, 1(2) 163-171, June 2006. 

If a technique is developed to readily and securely cover a polymer surface with a layer of adequate cells, hybrid-type artificial organs for use in vascular reconstruction and extracorporeal liver support, for example, may be possible. For cell-culture substrates several polymer surfaces are already available which distinctly favor cell covering. Cationic surfaces or immobilization of cell-adhesive proteins such as fibronectin and collagen have been utilized in these cases. 

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. 

Immobilization of chromatophores on the surface of the microbeads represents a key step in biosensor development. Fish chromatophores are anchorage-dependent cells that require compatible surface for attachment, subsequent spreading, and growth [5]. Generally, immobilization on the surface of small beads or microcarriers is a suitable method for the cultivation of anchorage-dependent cells. Van Wezel [13] first reported immobilization of cells on mammalian cells on diethyla-minoethyl (DEAE)-Sephadex A50. Subsequently this type of carrier was improved by optimizing... 

Preparation of polymeric carriers [166, 167] for the immobilization of cells, study of properties and porosity of the resulting cryogels... 

Chapter 19 deals with the physicochemical aspects of the most ubiquitous interface in living systems, the biological membrane. We conclude with Chapter 20, which deals with bioadhesion, that is, the accumulation of biological cells at interfaces. Bioadhesion may lead to adverse effects—for example, fouling of surfaces—but in other applications it is desired—for example, immobilization of cells in bioreactors. 

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