Cell immobilisation

Synthesis of industrial chemicals by microbial cells may be by fermentation (free, living cells), immobilised growing cells, immobilised resting cells or immobilised dead cells. 

Process B Genetic instability Poor enzyme stability Cofactor requirement Product (non-polar) inhibition Biocatalyst Free enzyme Free cells Immobilised enzyme Immobilised cells... 

A rapid activity loss (a few days) was observed with whole cells. Immobilisation increased the stability and continuous production of L-phenylalanine was possible using alginate bead immobilised cells of P. fluorescerts for 60 days. However, to achieve this the cofactor pyridoxalphosphate had to be continuously added to the beads to correct for the dissociation of the cofactor and loss from the cells. 

Cell immobilisation is costly in comparison to the production of free cells. 

Cell immobilisation is relatively costly because of the cost of the immobilisation procedure and of supplying cofactor. 

In fact, significant substrate concentration gradients may exist for cells immobilised in biofilm. Cells located close to the nutrient supply are likely to maintain higher quality and activity compared with cells located relatively further away, leading to differentiation in the quality or activity of the immobilised cell population. This differentiation is more pronounced if there are starvation regions. In practice, zero substrate concentration may exist inside the biofilm, because in these regions the cell physiology may be markedly different from that of the freely suspended cells. 

It is well known that pine enzymes change then behaviour and stability when they are immobilised. In the past two decades the immobilisation of microorganisms, cells and parts of cells has gradually been introduced into microbiology and biotechnology. The cell immobilisation techniques are modifications of the techniques developed for enzymes. However, the larger size of microbes has influenced the techniques. As for immobilised enzymes, two broad types of method have been used to immobilise microorganisms attachment to a support and entrapment. 

The effect of temperature on the rate of ethanol production is markedly different for free and immobilised systems. Thus while a constant increase in rate is observed with free S. cerevisiae as temperature is increased from 25 to 42 °C, a maximum occurs at 30 °C with cells immobilised in sodium alginate. The lower temperature optimum for immobilised systems may result from diffusional limitations of ethanol within the support matrix. At higher temperatures, ethanol production exceeds its rate of diffusion so that accumulation occurs within the beads. The achievement of inhibitory levels then causes the declines observed in the ethanol production rate. 

C. Heinzen, A. Berger, and I. Marison, Use of Vibration technology for jet break-up for encapsulation of cells and liquids in monodisperse microcapsules, in Fundamentals of Cell Immobilisation Biotechnology. Focus on Biotechnology Series, Vol. 8A, edited by V. Nedovic and R. Willaert (Kluwer Academic Publishers, Dordrecht, 2004), pp. 257-274. 

Immobilised cells have all the advantages of immobilised enzymes. Cell immobilisation is preferred for reactions catalysed by intracellular enzymes because it avoids tedious and expensive extraction and purification procedures, which often result in preparations of low yield and stab ty. 

Ray NG, Tung AS, Hayman EG, Vournakis JN Runstadler PW Jr (1990) Continuous cell culture in fluidized bed reactors cultivation of hybridomas and recombinant CHO cells immobilised in collagen microspheres. Annals of the New York Academy of Sciences, Biochemical Engineering VI 589 443-457. 

G. Zhu, T.S. Chung, and K. C. Loh, Activated carbon-filled cellulose acetate hollow fibre membrane for cell immobilisation and phenol degradation. J. Applied Polymer Science 76, 695-707 (2000). 

Studies were carried out on the antibacterial activity of insoluble pyridinium-type polymers with different stractures against Escherichia coh snspended in sterilised and distilled water nsing a colony connt method. The results reveal that the antibacterial activity of insoluble pyridinium-type polymers, except for one containing 1-, is characterised by an ability to capture bacterial cells in a living state by adsorption or adhesion, with the process of capturing bacterial cells being at least partially irreversible. This featnre differs from the antibacterial activity of the corresponding soluble polymers, which is characterised by the ability to kill bacterial cells in water. Also, insoluble pyridinium-type polymers can captme dead bacterial cells. The implication is that insoluble pyridinium-type polymers possess broad prospects for development in new water treatment techniques and whole-cell immobilisation techniques. 28 refs. 

RAPID AND ONSITE BOD SENSING SYSTEM BY LUMINOUS CELLS-IMMOBILISED-CHIP... 

Experimental Method for Formation of the Support. Samples (each of 1.3 mmol) of the metal hydroxides for use in cell immobilisation were prepared from solutions of their tetrachlorides (titanium (IV) chloride 15% w/v in 15% w/v hydrochloric acid (BDH, Poole, England) and zirconium (IV) chloride (BDH) 0.65 M in 1.0 M hydrochloric acid) by the slow addition of... 

M ammonium hydroxide to neutrality (pH 7.0). The samples were washed with saline solution (0.9% w/v, 3x5.0 ml) to remove ammonium ions and then used for cell immobilisation studies as below. 

Experimental Method for Immobilisation of Cells. The procedure for cell immobilisation is very simple and is illustrated by the following example. A suspension (in 10 ml 0.9w/v saline) of Escherichia coli cells (A qq 0.216) was mixed with a sample of the metal hydroxide as prepared as above (pH 5-7) and agitated gently for 5 min at room temperature. The mixture was then allowed to stand at room temperature and the suspension settled out, leaving a clear supernatant... 

If this simple means of cell immobilisation were applied to other microorganisms it could well result in further immobilised cell reactors of this sort, for the selective production of commercially important biochemical and pharmaceutical compounds. Magnetic forms of the hydrous... 

Marison, A. Peters, and C. Heinzen. Liquid core capsules for applications in biotechnology. In V. Nedovic and R. Willaert, eds.. Fundamentals of Cell Immobilisation Biotechnology, number 8A in Focus on Biotechnology. Springer, Dordrecht, the Netherlands, January 2004, pp. 185-204. 

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