Efficient polycyclic aromatic hydrocarbons dihydroxylation in direct micellar systems

✍ Scribed by Demetrio Randazzo; Debora Berti; Fabrizio Briganti; Piero Baglioni; Andrea Scozzafava; Patrizia Di Gennaro; Enrica Galli; Giuseppina Bestetti

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 177 KB
• Volume: 74
• Category: Article
• ISSN: 0006-3592
• DOI: 10.1002/bit.1113

✦ Synopsis

Abstract

Optimization of whole‐cell bioconversion of the polycyclic aromatic hydrocarbons (PAHs) anthracene, phenanthrene, and naphthalene to the enantiomerically pure corresponding cis‐dihydroxydihydro derivatives by the Escherichia coli JM109 (pPS1778) recombinant strain, carrying the naphthalene dioxygenase and corresponding regulatory genes cloned from Pseudomonas fluorescens N3, in micellar systems, is presented. We show that direct microemulsion systems, 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 relatively high concentrations (initial concentrations in the reaction medium ≥10 m__M__ for naphthalene and phenanthrene and ≥2 m__M__ for anthracene), and allow for more efficient substrate bioconversion. These media, while not affecting bacteria viability and performance, provide increased efficiency and final product yields (100% for naphthalene, >30% for anthracene, >60% for phenanthrene). The phase behavior of the direct microemulsion systems for the different substrates and oils utilized was monitored as a function of their volume fraction by light scattering experiments, and related to the bioconversion results. For anthracene and phenanthrene, the dihydroxylated products have an inhibitory effect on the conversion reactions, thus hindering complete turnover of the substrates. We ascertain that such inhibition is reversible because removal of the products formed allowed the process to start over at rates comparable to initial rates. To allow for complete conversion of the PAHs tested a stepwise or continuous separation of the product formed from the micellar reaction environment is being developed. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 74: 240–248, 2001.