Dioxygenation of naphthalene by Pseudomonas fluorescens N3 dioxygenase: optimization of the process parameters

The bioconversion of naphthalene to the 1,2-dihydro-1,2-dihydroxy derivative was performed in good yield using an Escherichia coli recombinant strain carrying Pseudomonas fluorescens N3 dioxygenase. However, the efficiency of such transformation is affected by many process parameters, and their optimization is essential to the scaling up of the process. The following process parameters were considered for optimization: cell concentration together with the corresponding glucose concentration (DCW/L); pH of medium; temperature; stirring speed; air flow; substrate concentration; Fe(2+) concentration; microelements concentration; reaction volume. We used a two-step multivariate experimental design to select important variables and assign them optimal values. The most significant parameters were selected by adopting a Plackett-Burman design, and were then correlated, using a full factorial design, with the experimental results. The experimental results illustrate that the optimized process of recombinant whole cell biotransformation in two-liquid phase systems enhances the naphthalene dihydrodiol yield threefold. This biotransformation opens the way to future experiments involving different substrates.