Redox whole-cell biotransformations

Multi-Enzyme Systems in Whole-Cell Biotransformations and Expression of Redox Systems 55... 

To circumvent the cofactor regeneration problem, redox biotransformations are also carried out in whole cells - for example, baker s yeast [28, 29] or engineered Escherichia coli cells [30] - using the intracellular cofactor pool and inherent or recombinant regeneration systems. 

At the same time, engineering rules that apply to whole-cell redox reactions have to be taken into account. In general, aeration and/or carbon dioxide production is involved, and plug flow reactors are not appropriate. Moreover, oxygen transfer to immobilized cells is not very efficient. Consequently, continuous reactors are not very suitable for redox biotransformations with whole cells [12]. These biotransformations can best be carried out in (fed) batch reactors with free cells. Since the production of the cells will also involve a (fed) batch process, these processes may easily be combined. Then, the cells are produced in a fed-batch fer-... 

Whole-cell biocatalysts are basically one-pot cascade reactions, with various enzymatic reactions being carried out concurrently within individual cells. Compared to purified enzymes, whole-cell biocatalysts are inexpensive and easily scalable and can be stably stored indefinitely. Certain enzymes are unstable and lose activity when purified from cells. Living cells also contain and regenerate otherwise expensive redox cofactors and, with metabolic engineering, can produce desired chemicals from inexpensive carbon and nitrogen sources [66, 67]. On the other hand, a major downside of using whole cells for biotransformations is the increased cost of product extrachon and purification from fermentahon broths. One also has to consider the... 

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