Biphasic bioconversion of naphthalenes into dihydrodiols : solvent effects and substrate differences

Since many years, we have been interested in whole cell bioconversions of aromatic hydrocarbons into derivatives that can be of interest as synthetic intermediates. We have developed recombinant bacteria containing oxygenases from Pseudomonas strains. In particular, we isolated the naphthalene dioxygenase of P. fluorescens N3 responsible of the conversion of substituted naphthalenes into the corresponding dihydrodiols with unique absolute configuration. In order to increase the bioconversion yield and the system performance we studied the possibility of using a culture where the substrate is dissolved in an appropriate hydrophobic solvent. Preliminary results concerned the effects on the naphthalene transformation. Now, to further our understanding, we extend our experiments to some substituted naphthalenes. In this perspective, several flask transformations and some reactor experiments have been performed. The results show that the solvent role is highly affected by the substratesubstrate used and that some other important bioconversion variables influence the transformation. It appears clear that substrate bioavailability is definitely an essential condition, which is influenced by the solvent selection, the solvent-water phase ratio, the presence of surfactants, and, not last, the transfer mechanism. On the other hand, the absolute yield also depends on the possibility of maintaining the enzyme activity for long enough time. Our results will be presented and discussed together with future directions and developments. In this respect, we began a series of reactor experiments using a multivariate approach where the role of some variables has been explicitly investigated.