Direct micellar systems as a tool to improve the efficiency of aromatic substrate conversion for fine chemicals production

Whole-cell bioconversion of naphthalene to (+)-cis-(1R,2S)-dihydroxy-1,2-di hydronaphthalene by Escherichia coli JM109(pPS1778) recombinant strain, car rying naphthalene dioxygenase and regulatory genes cloned from Pseudomonas fluorescens N3, in direct micellar systems is optimized as an example of fi ne chemicals bioproduction from scarcely water-soluble substrates. The oxyg en insertion into the aromatic substrate, which stops at the enantiomerical ly pure cis dihydroxylated product, is performed in direct microemulsion sy stems, where a non-ionic surfactant stabilizes naphthalene containing oil d roplets in an aqueous medium. These media provide an increased substrate so lubility so that a homogeneous reaction can be carried out, while not affec ting bacteria viability and performances. The influence of the chemical nat ure of the oil is investigated. The phase behavior of the direct microemuls ion system was monitored for three different oils as a function their volum e fraction and characterized through light scattering. The addition of isop ropyl palmitate, oleic acid, or glyceryl trioleate, 0.6-1.2% v/v to the mic ellar systems, led to an increase of the substrate concentration in the sol ution and particularly its bioavailability, allowing faster catalytic conve rsions. All these systems resulted in being suitable for catalytic conversi ons of aromatic compounds. Although the nature of the oil does have a deep effect on the phase behavior of the micellar systems, in the present invest igation no differences in the yields and in the rates of product formation of the enzymatic system were observed on changing the oil, thus showing tha t in this case the substrate concentration or bioavailability is not the ra te-limiting step. (C) 2000 Elsevier Science Inc. All rights reserved.