Development of biocatalysts carrying naphthalene dioxygenase and dihydrodiol dehydrogenase genes inducible in aerobic and anaerobic conditions

We developed biocatalysts carrying naphthalene dioxygenase and dihydrodiol dehydrogenase genes cloned from plasmid pN3 of Pseudomonas fluorescens N3 i nvolved in naphthalene degradation, as an alternative approach to the produ ction of hydroxylated compounds by chemical synthesis. Naphthalene dioxygen ase is responsible for hydroxylation of the hydrocarbon into the correspond ing 1,2-dihydro-1,2-dihydroxy derivative and dihydrodiol dehydrogenase is i nvolved in the subsequent transformation into the 1,2-dihydroxy derivative. The first reaction strictly requires the presence of oxygen, essential for the dioxygenation reaction, while the second one can also be performed in anaerobic conditions that are optimal to avoid the easy oxidation of biocon version products. Consequently, we constructed biocatalysts carrying the ge nes responsible for the biotransformation of hydrocarbons, inducible under aerobic and anaerobic conditions. We cloned the dioxygenase gene under its promoter, inducible by salicylic acid and the dihydrodiol dehydrogenase und er the Pnar promoter of Escherichia coli, inducible by nitrate, in a nitrog en atmosphere, in order to develop biological systems with the possibility of controlling the expression of the cloned genes by the shift from aerobic to anaerobic conditions. Bioconversion experiments performed in aerobic co nditions showed dihydrodiol production and dehydrogenase repression; as soo n as cultures were switched to nitrogen, dihydrodiol dehydrogenation with a n efficient production of 1,2-dihydroxyderivatives was observed. (C) 2000 E ditions scientifiques et medicales Elsevier SAS.