Efficient polycyclic aromatic hydrocarbons dihydroxylation in direct micellar systems

Optimization of whole-cell bioconversion of the polycyclic aromatic hydroca rbons (PAHs) anthracene, phenanthrene, and naphthalene to the enantiomerica lly pure corresponding cis-dihydroxydihydro derivatives by the Escherichia coil JM109 (pPS1778) recombinant strain, carrying the naphthalene dioxygena se and corresponding regulatory genes cloned from Pseudomonas fluorescens N 3, in micellar systems, is presented. We show that direct microemulsion sys tems, where a nonionic surfactant such as 1.5% (v/v) Triton X-100 plus 0.6% to 1.0% (v/v) selected oils are able to solubilize the PAHs tested at rela tively high concentrations (initial concentrations in the reaction medium g reater than or equal to 10 mM for naphthalene and phenanthrene and greater than or equal to2 mM for anthracene), and allow for more efficient substrat e bioconversion. These media, while not affecting bacteria viability and pe rformance, provide increased efficiency and final product yields (100% for naphthalene, >30% for anthracene, >60% for phenanthrene). The phase behavio r of the direct microemulsion systems for the different substrates and oils utilized was monitored as a function of their volume fraction by light sca ttering experiments, and related to the bioconversion results. For anthrace ne and phenanthrene, the dihydroxylated products have an inhibitory effect on the conversion reactions, thus hindering complete turnover of the substr ates. We ascertain that such inhibition is reversible because removal of th e products formed allowed the process to start over at rates comparable to initial rates. To allow for complete conversion of the PAHs tested a stepwi se or continuous separation of the product formed from the micellar reactio n environment is being developed. (C) 2001 John Wiley & Sons, Inc.