Extractive bioconversion

A prehminary study of the use of larch AGs in aqueous two-phase systems [394] revealed that this polysaccharide provides a low-cost alternative to fractionated dextrans for use in aqueous two-phase, two-polymer systems with polyethylene glycol (PEG). The narrow molecular-weight distribution (Mw/Mn of 1-2) and low viscosity at high concentration of AG can be exploited for reproducible separations of proteins under a variety of conditions. The AG/PEG systems were used with success for batch extractive bioconversions of cornstarch to cyclodextrin and glucose. 

Other applications besides purification of biomolecules are affinity partitioning (Labrou, 1994), extractive bioconversions (Andersson, 1990 Kaul, 1991 Zijlstra, 1998), liquid-liquid partition chromatography, and analytical assays. Although industrial applications of aqueous two-phase systems have not gained widespread use to date, practical and economic feasibility has been proved (Tjemeld, 1990 Cunha, 2002). 

R. KAurand B. Mattiasson, Extractive bioconversions in aqueous two-phase systems, Bioproc. Technol. 1991, 11,... 

Fernandes, P., Prazeres, D.M.F. and Cabral, J.M.S. (2003) Membrane-assisted extractive bioconversions, in Advances in Biochemical Engineering/Biotechnology (eds), Springer, p. 115. 

Monitoring Enzymes That Degrade Macromolecular Substrates by Extractive Bioconversion in Aqueous TVo-Phase Systems... 

Hahn-Hagerdal, B. Mattiasson, B. Albertsson, P.-A. "Extractive Bioconversion in Aqueous Two-Phase Systems. A Model Study on the Conversion of Cellulose to Ethanol" Biotech. Letters. 1981, 3, 2, pp 53-58. 

Although CO2 is inhibitory to microbes, compressed hydrocarbon solvents may be appropriate for extractive bioconversions and extractions in biphasic (aqueous-compressed solvent) systems. Our laboratory investigated the metabolic activity of the anaerobic, thermophilic bacteria Clostridium ther-mocellum as a model system (45). Thermophilic bacteria have a distinct advantage over conventional yeasts for ethanol production in their ability to use a variety of inexpensive biomass feedstocks. Extractive fermentation using compressed solvents is an approach to address the end-product toxicity of these bacteria to ethanol and improve the economic viability of biofuel production by thermophilic organisms. 

Fernandes P, Prazeres DMF, Cabral JMS. Membrane-assisted extractive bioconversions. Adv Biochem Eng Biotechnol 2003 80 115-148. 

Lopez JL, Matson SL, Stanley TJ, and QuinnJA, Liquid/liquid extractive membrane reactors. In Mattiasson B, and Holst, eds. Extractive Bioconversions Bioprocess Technologies Series, Marcel Dekker, New York, 1990 pp. 27—66. 

An example of aldehyde formation is the production of isovaleraldehyde by Gluconobacter oxydans R (Fig. 16.2-45) 202, 206. Glycerol-grown Gluconobacter oxydans slowly oxidizes 3-methyl-l-butanol to isovaleraldehyde, with yields of over 90%. The product was recovered by bisulphite trapping or cold traps 202. Extractive bioconversion in a hollow-fiber membrane bioreactor allowed continuous produc-... 

Aqueous two-phase systems are generated by mixing aqueous solutions of two water-soluble polymers, or a polymer and a salt. These systems offer extremely mild conditions for separation of cells, organelles, proteins and other biomolecules, in biochemical processes. Considerable attention has been directed towards the use of the two-phase systems in several areas of biotechnology. The present paper summarizes the state of the art concerning extractive bioconversions for production of small as well as macromolecules, and protein purification using aqueous two-phase system. 

Figure 1. Principle for extractive bioconversion in aqueous two-phase systems, where the biocatalyst is temporarily immobilized in the droplets of one of the phases. Reproduced with permission from Ref. 7. Copyright 1984. Society of Chemical Industry.

One of the common side effects observed during extractive bioconversion is the accumulation of unwanted by-products in the system which may affect the productivity during continuous operation (14). The build up of glycerol and other non-volatile products was shown to decrease the ethanol yields during repeated fermentations in a two-phase system (12). The problem was, however, solved by dialysing the fermentation broth and also adding more yeast cells. It appears that the combination of ultrafiltration with the phase system may circumvent the problem of by-product inhibition in most of the cases. 

These studies, therefore, set the basis for a continuous system for extractive bioconversion of steroids. The interesting point that comes to notice is that the combination of two techniques such as aqueous two-phase separation, and adsorption, which are generally used individually for performing extractive bioconversions, could be advantageous for efficient product recovery in case of fine chemicals as well. 

The versatility and the potential of aqueous two-phase systems in future biotechnology has been amply demonstrated. The applications described here deal with extractive bioconversions, isolation and purification of proteins. Biochemical analyses in terms of binding assays have also been successfully applied in the two-phase systems... 

D. Stark. Extractive bioconversion of 2-phenylethanol from L-phenylalanine by Saccharomyces cere-visiae. PhD thesis, EPFL, Lausanne, 2001. 

NielsenL,LarssonM,HolstO,MattiassonB. 1988.Adsorption for extractive bioconversion applied to the acetone-butanol fermentation. Appl. Microbiol. Biotechnol. 28 335-339. 

Keywords. Extractive bioconversions. Membrane reactors. Bioreactors, Process integration... 

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