METABOLISM OF DIBENZOTHIOPHENE AND NAPHTHALENE IN PSEUDOMONAS STRAINS- COMPLETE DNA-SEQUENCE OF AN UPPER NAPHTHALENE CATABOLIC PATHWAY

From a soil isolate, Pseudomonas strain C18, we cloned and sequenced a 9.8-kb DNA fragment that encodes dibenzothiophene-degrading enzymes. Nine open reading frames were identified and designated doxABDEF-GHIJ. Collectively, we refer to these genes as the DOX pathway. At the nucl eotide level, doxABD are identical to the ndoABC genes that encode nap hthalene dioxygenase of Pseudomonas putida. The DoxG protein is 97% id entical to NahC (1,2-dihydroxynaphthalene dioxygenase) of P. putida. D oxE has 37% identity with cis-toluene dihydrodiol dehydrogenase. DoxF is similar to the aldehyde dehydrogenases of many organisms. The predi cted DoxHIJ proteins have no obvious sequence similarities to known pr oteins. Gas chromatography with a flame ionization detector and mass s pectroscopy confirmed that the DOX proteins convert naphthalene to sal icylate and convert phenanthrene to 1-hydroxy-2-naphthoic acid. doxI m utants convert naphthalene to trans-o-hydroxybenzylidenepyruvate, indi cating that the DoxI protein is similar to NahE (trans-o-hydroxybenzyl idenepyruvate hydratase-aldolase). Comparison of the DOX sequence with restriction maps of cloned naphthalene catabolic pathway (NAH) genes revealed many conserved restriction sites. The DOX gene arrangement is identical to that proposed for NAH, except that the NAH equivalent of doxH has not been recognized. DoxH may be involved in the conversion of y-4-(2'-oxo-3,5-cyclohexadienyl)-buta-2,4-dienoate to cis-o-hydroxy benzylidenopyruvate. doxJ encodes an enzyme similar to NahD (isomerase ). Our findings indicate that a single genetic pathway controls the me tabolism of dibenzothiophene, naphthalene, and phenanthrene in strain C18 and that the DOX sequence encodes a complete upper naphthalene cat abolic pathway similar to NAH.