Premium
The efficiency of recombinant Escherichia coli as biocatalyst for stereospecific epoxidation
Author(s) -
Park JinByung,
Bühler Bruno,
Habicher Tilo,
Hauer Bernhard,
Panke Sven,
Witholt Bernard,
Schmid Andreas
Publication year - 2006
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.21037
Subject(s) - biocatalysis , chemistry , product inhibition , bioconversion , bioproduction , biotransformation , pseudomonas putida , styrene oxide , substrate (aquarium) , styrene , biochemistry , organic chemistry , catalysis , fermentation , enzyme , biology , non competitive inhibition , reaction mechanism , ecology , polymer , copolymer
Styrene is efficiently converted into ( S )‐styrene oxide by growing Escherichia coli expressing the styrene monooxygenase genes styAB of Pseudomonas sp. strain VLB120 in an organic/aqueous emulsion. Now, we investigated factors influencing the epoxidation activity of recombinant E. coli with the aim to improve the process in terms of product concentration and volumetric productivity. The catalytic activity of recombinant E. coli was not stable and decreased with reaction time. Kinetic analyses and the independence of the whole‐cell activity on substrate and biocatalyst concentrations indicated that the maximal specific biocatalyst activity was not exploited under process conditions and that substrate mass transfer and enzyme inhibition did not limit bioconversion performance. Elevated styrene oxide concentrations, however, were shown to promote acetic acid formation, membrane permeabilization, and cell lysis, and to reduce growth rate and colony‐forming activity. During biotransformations, when cell viability was additionally reduced by styAB overexpression, such effects coincided with decreasing specific epoxidation rates and metabolic activity. This clearly indicated that biocatalyst performance was reduced as a result of product toxicity. The results point to a product toxicity‐induced biological energy shortage reducing the biocatalyst activity under process conditions. By reducing exposure time of the biocatalyst to the product and increasing biocatalyst concentrations, volumetric productivities were increased up to 1,800 µmol/min/liter aqueous phase (with an average of 8.4 g/L aq ·h). This represents the highest productivity reported for oxygenase‐based whole‐cell biocatalysis involving toxic products. © 2006 Wiley Periodicals, Inc.