Cell, immobilized

Like enzymes, whole cells are sometime immobilized by attachment to a surface or by entrapment within a carrier material. One motivation for this is similar to the motivation for using biomass recycle in a continuous process. The cells are grown under optimal conditions for cell growth but are used at conditions optimized for transformation of substrate. A great variety of reactor types have been proposed including packed beds, fluidized and spouted beds, and air-lift reactors. A semicommercial process for beer used an air-lift reactor to achieve reaction times of 1 day compared with 5-7 days for the normal batch process. Unfortunately, the beer suffered from a mismatched flavour profile that was attributed to mass transfer limitations. 

It has been proposed that some enzymes exist in active and inactive forms that are in equilibrium. The active form binds substrate molecules for subsequent reaction while the inactive form does not. The overall reaction mechanism might be 

Set the time derivatives in Example 12.6 to zero to find the steady-state design equations for a CSTR with a Michaelis-Menten reaction. An analytical solution is possible. Find the solution and compare it with the solution in Example 12.3. Under what conditions does the quasisteady solution in Example 12.3 become identical to the general solution in Example 12.6  

Wang et al. report the death kinetics of Bacillus stearothermophilus spores using wet, thermal sterilization. Twenty minutes at 110°C reduces the viable count by a factor of lO . The activation temperature, E/Rg, is 34,200 K. How long will it take to deactivate by a factor of lO  

A literature value for the Monod constant for a Saccharomyces cerevisiae fermentation is. S ,s = 25mg/liter. How does this affect the simulation in Example 12.7  

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Enzymatic hydrolysis is also used for the preparation of L-amino acids. Racemic D- and L-amino acids and their acyl-derivatives obtained chemically can be resolved enzymatically to yield their natural L-forms. Aminoacylases such as that from Pispergillus OTj e specifically hydrolyze L-enantiomers of acyl-DL-amino acids. The resulting L-amino acid can be separated readily from the unchanged acyl-D form which is racemized and subjected to further hydrolysis. Several L-amino acids, eg, methionine [63-68-3], phenylalanine [63-91-2], tryptophan [73-22-3], and valine [72-18-4] have been manufactured by this process in Japan and production costs have been reduced by 40% through the appHcation of immobilized cell technology (75). Cyclohexane chloride, which is a by-product in nylon manufacture, is chemically converted to DL-amino-S-caprolactam [105-60-2] (23) which is resolved and/or racemized to (24)... 

The hydrolysis of nitriles can be carried out with either isolated enzymes or immobilized cells. Eor example, resting cells of P. chlororaphis can accumulate up to 400 g/L of acrylamide in 8 h, provided acrylonitrile is added gradually to avoid nitrile hydratase inhibition (116). The degree of acrylonitrile conversion to acrylamide is 99% without any formation of acryUc acid. Because of its high efficiency the process has been commercialized and currentiy is used by Nitto Chemical Industry Co. on a multithousand ton scale. 

Lasldn, A., Enzymes and Immobilized Cells in Biotechnology, Butter-worth/Heinemann, Stoneham, Massachusetts, 1985. 

Immobilized cell Technique used for the fixation of enzymes or cells onto a solid support. 

Najafpour, G.D., Younesi, H. and Ku Ismail, K.S., Ethanol Fermentation in Immobilized Cell Reactor (ICR) Using Saccharomyces cerevisiae , Bioresource Technology, vol. 92/3, 2004, pp. 251-260. 

Although the use of fermentation to produce ethanol is an ancient technology, more efficient immobilized-cell, continuous processes have been conceived, and Japan has estabhshed the first demonstration-scale plant. 

Volume 11 Immobilized Cells Basics and Applications (Wijffels et al.. Editors)... 

It is possible to carry out experiments with immobilized cells in essentially nonaqueous media (Rothenburger and Atlas 1993), and this could prove an attractive strategy for compounds with limited water solubility, provided that solvents can be found that are compatible with the solubility of the substrate and the sensitivity of the cells to organic solvents. 

Rothenbnrger S, RM Atlas (1993) Hydroxylation and biodegradation of 6-methylquinoline by psendomonads in aqneons and nonaqueous immobilized-cell bioreactors. Appl Environ Microbiol 59 2139-2144. 

Applications of the organic solvents in fluidized-bed reactors have also been investigated, particularly with immobilized cells (Table 5). This type of reactor has several advantages over a fixed-bed reactor, namely, reduced coalescence of the emulsion particles, lower pressure at high flow rate, and less channeling and plugging. 

FIGURE 18.13 Allied Signal Immobilized Cell Bioreactor (ICB). 

Borja, R. and Banks, C J., Semicontinuous anaerobic digestion of soft drink wastewater in immobilized cell bioreactors, Biotechnology Letters, 15, 767-772, 1993. 

A thermally stable NHase from Comamonas testosteroni 5-MGAM-4D (ATCC 55 744) [22] was recombinantly expressed in Escherichia coli, and the resulting transformant cells immobilized in alginate beads that were subsequently chemically cross-linked with glutaraldehyde and polyethylenimine. This immobilized cell catalyst (at 0.5 % dew per reaction volume) was added to an aqueous reaction mixture containing 32wt% 3-cyanopyridine at 25 °C, and a quantitative conversion to nicotinamide was obtained. The versatility of this catalyst system was further illustrated by a systematic study of substrates, which included... 

D-4-Hydroxyphenyl glycine 9 Ampicillin/ amoxycillin Antibacterial Hydrolysis Bacillus brevis Immobilized cells [8]... 

Nicotinamide 10 Nicotinamide Treatment of pellagra Hydrolysis Rhodococcus rhodochrous Immobilized cells [7]... 

D-Aspartic acid 16 Apoxycillin Antibacterial Decarboxylation Pseudomonas dacunhae Immobilized cells [10]... 

In order to extend the biocatalytic activities of the biotransformation processes and reduce the frequency of producing cell mass and undesirable side products, immobilized-cell technology has been successfully applied to the whole-cell biotransformation processes. In addition to the three commercial immobilized whole-cell biotransformation processes shown in Table 10.1, examples of immobilization of three different microorganisms for whole-cell biotransformations are shown below to demonstrate the broad application of the immobilized whole-cell biotransformation processes. 

The significance of the application of immobilized-cell technology in the production of industrially important chemicals is exemplified by the production of acrylamide by immobilized Escherichia coli cells containing nitrile hydratase. The immobilized Escherichia coli cells convert acrylonitrile to acrylamide, yielding 6000 tons of acrylamide per year by this process [28]. 

Tan et al. [29] demonstrated the use of a plug flow reactor of immobilized Lactobacillus kefiri cells for the synthesis of the intermediate (5I )-hydroxyhexane-2-one. This immobilized-cell reactor operated at a maximum conversion yield of 100% and a selectivity of 95%. The production of (5/ )-hydroxyhexane-2-one was extended to an operation time of 6 days. During this time (91 residence times), a space-time yield of 87gL xday 1 and a productivity of 07 8 gwet cell weight 1 were obtained. 

Sitosterol is an abundant and low-cost raw material for the production of pharmaceutical steroids. 4-Androstene-3,17-dione, the precursor for the synthesis of corticosteroid hormones, can be derived from the side-chain cleavage of/3-sitosterol. Immobilized cells of Mycobacterium sp. NRRL B-3805 on Celite matrix (80-120 mesh) was found to be effective in cleaving the side chain of /3-sitosterol (5gL ) with a molar conversion yield of 70% in 50 h [30],... 

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