Patents and literature: Immobilized Biocatalysts

Development of a Combined Biological and Chemical Process for Production of Industrial Aromatics from Renewable Resources

Production of industrial aromatic chemicals from renewable resources could provide a competitive alternative to traditional chemical synthesis routes. This review describes the engineering of microorganisms for the production of p-hydroxycinnamic acid (pHCA) and p-hydroxystyrene (pHS) from glucose. The initial process concept was demonstrated using a tyrosine-producing Escherichia coli strain that overexpressed both fungal phenylalanine/tyrosine ammonia lyase (PAL) and bacterial pHCA decarboxylase (pdc) genes. Further development of this bioprocess resulted in uncoupling the pHCA and pHS production steps to mitigate their toxicity to the production host. The final process consists of a fermentation step to convert glucose to tyrosine using a tyrosine-overproducing E. coli strain. This step is followed by a single biotransformation reaction to deaminate tyrosine to pHCA through immobilized E. coli cells that overexpress the Rhodotorula glutinis PAL gene. Finally, chemical decarboxylation of pHCA produces pHS. This multifaceted approach, which integrates biology, chemistry, and engineering, has allowed development of an economical process at scales suitable for industrial applications.

On the merits of viable-cell immobilisation

Many advantages have been claimed over the years for the use of immobilised cells, both as enzyme systems and as whole viable cell systems for complete fermentation reactions. However, few of the claims have been fully substantiated, and may not even be entirely justified. Most research is involved with single applications and the best that can be hoped for is some evidence that immobilised cells in each of these individual cases display some advantage over the equivalent free cell system. The purpose of this review is to assess the merits of viable cell immobilisation in the light of published literature and to elucidate the underlying mechanisms. Particular attention is paid to the generally unanticipated, but widely observed enhanced stability of immobilised cell fermentation processes.