Microbial cells living immobilised on metal hydroxides

THE immobilisation of enzymes by attachment to water-insoluble materials has received considerable attention recently 1 , both for academic reasons and for possible industrial applications. A logical extension of this approach, especially where multi-stage enzymic reactions are being considered, is the immobilisation of microorganisms, which are often the source of many enzyme preparations. The advantages of such an approach are immediately obvious. The tedious and time consuming procedures for enzyme extraction and purification are instantly eliminated, cofactors and coenzymes are readily at hand, the cellular enzymes are often organised into the requisite metabolic pathways and problems associated with enzyme instability may also be avoided. Furthermore, the use of immobilised cells would avoid the problem in industrial processes of separating the product from the enzyme. The immobilisation of cells by the standard glutaraldehyde procedure, however, causes their decease, and entrapment in polyacrylamide gel is commonly used instead to achieve immobilisation 2,3 . This method produces a minimum of interaction between the microbial cell and the insoluble matrix, thus maximising the probability of the cell's survival. On the other hand, the availability of the cell to any intended substrate is seriously reduced, since it can reach the cell only by diffusion. An alternative approach of immobilising cells on collagen, by the formation of a stable network of multiple ionic (salt) linkages, hydrogen bonds and Van der Waals' interactions has been successful 4 . We have now pursued an independent approach and report here the successful immobilisation of cells on the hydroxides (hydroxyoxides) of titanium (IV) and zirconium (IV) by a chelation process.