Immobilized whole cells as effective catalysts for chiral alcohol production

Abstract

Recombinant Escherichia coli overexpressing the gene LbADH, which encodes for an alcohol dehydrogenase from Lactobacillus brevis, was successfully transformed and cultured. The cells are able to catalyze the reduction of pro-chiral ketones, e.g. ethyl acetoacetate into R-()ethyl hydroxybutyrate (EHB) with high conversion and enantiomeric excess 99%. Immobilizing the whole cells in alginate beads leads to a catalyst with improved stability and ease of handling while maintaining the high activity of the free cells. The whole-cell catalyst was tested in a stirred batch reactor (CSTR) and in a continuously operated packed-bed reactor. An Mg2+ concentration of 2 mM was crucial for maintaining the activity of the biocatalyst. After a partial optimization of the process conditions, a productivity of 1.4 gEHB gwcw -1 h-1 could be maintained in a continuous flow reactor over a prolonged period of time. © CSIRO 2009.