The potentials of using organic reaction media in biotechnological conversions have already been demonstrated in several experimental studies. Examples of possible advantages are: possibility of higher substrate and/or product concentrations, favorable shift of reaction equilibria, reduced substrate and/or product inhibition, and facilitated product recovery. Especially water/organic solvent two-phase systems seem to possess several of these advantages. The solvent type will highly affect kinetics and stability of the (immobilized) biocatalyst, solubility and partitioning of reactants/products, and product recovery. Therefore the solvent choice can have a large influence on the economics of the two-liquid-phase biocatalytic process. Immobilization of the biocatalyst may be useful to provide protection against denaturating solvent effects. The polarity of the employed support material will also be decisive for the partitioning of substrates and products among the various phases. A classification of biphasic systems, which is based on the possible types of theoretical concentration profiles and aqueous phase configurations, is discussed. Reversed micelles and aqueous two-liquid-phase systems can be considered as special cases. The design of two-liquid-phase bioreactors is dependent on the state of the biocatalyst, free or immobilized, and on the necessity for emulsification of one of the two liquid phases in the other. Many mass-transfer resistances, e.g. across the liquid/liquid interface, in the aqueous phase, across the liquid/solid interface, and in the biocatalyst phase, can limit the overall reaction rate. The epoxidation of alkenes in water/solvent two-phase systems is discussed to give an example of the scope of biotechnological processes that is obtained by using organic media. Finally, a design calculation of a packed-bed organic-liquid-phasel immobilized-biocatalyst reactor for the epoxidation of propene is given to illustrate some of the above aspects.

Biocatalysis in Organic Media

Gel entrapment and micro-encapsulation: methods, applications and engineering principles

The use of various whole-cell organisms as tools for monitoring water contaminants is reviewed and evaluated. Their suitability and value for assessing a range of environmental problems from the impact of pollution, homeland defense issues, conservation, and the long-term degradation and recovery of ecosystems is discussed. Guidelines are provided for the choice of appropriate bioreporter organisms, transducers, and immobilization methods. Examples of the use of a broad spectrum of whole-cell bioreporters in assessing a variety of environmental problems are summarized.

Whole-cell aquatic biosensors.

Microorganisms able to grow on low molecular weight aliphatic hydrocarbon gases, i.e. the n-alkanes, ethane, propane and butane, and the terminal alkenes, ethylene, propylene and butylene, are not uncommon but mainly belong to certain taxonomic groups. These microbes are described in this review together with the pathways by which the hydrocarbons are assimilated. Microbial oxidation of the volatile alkadiene, isoprene, is also discussed. Avenues for possible commercial exploitation of these metabolic activities are also reviewed. Short-chain n-alkane-utilising organisms have been investigated as tools in petroleum exploration and for production of single cell protein. More recently microbes grown on gaseous hydrocarbons other than methane have been evaluated for use in biotechnological production of epoxides, synthesis of chiral epoxyalkanes and as catalysts in bioremediation systems. Copyright © 2005 Society of Chemical Industry

Utilisation of C2–C4 gaseous hydrocarbons and isoprene by microorganisms

Biocatalysis in multi-phase reaction mixtures containing organic liquids.

Nocardia corallina B276 cells were immobilized by emulsification with liquid paraffin and an antifoam agent at room temperature. The immobilized cells were studied for their ability to carry out the formation of propylene oxide from propylene and oxygen. The evaluations were done with the cells in a bubble-type reactor with a continuous gas feed of 5% propylene and 11.6-95% oxygen, with the balance nitrogen. By using liquid paraffin and antifoam, both the epoxidation activity and the stability were improved, especially for the P-1-200 strain, over that for nonimmobilized cells. The N. corallina cells showed an apparent preference for a hydrophobic, as compared to a hydrophilic, environment. The propylene-oxide-forming activity of the immobilized cells was higher at 40 than at 30 degrees C reactor temperature and with 20% (versus 95%) oxygen in the feed. The stability was markedly better at 30 degrees C and with 20% oxygen. High gas flowrates gave increased apparent activity probably because of less resistance to substrate mass transfer. The effects of pH were minor. The role of glucose as the energy source for regeneration of cofactors for the monooxygenase system also is discussed.

Richard S. Silver

Papers

Formation of propylene oxide by Nocardia corallina immobilized in liquid paraffin.

Epoxidation of propylene utilizing Nocardia corallina immobilized by gel entrapment or adsorption