DINITROTOLUENE DIOXYGENASE FROM BURKHOLDERIA SP STRAIN DNT - SIMILARITY TO NAPHTHALENE DIOXYGENASE

2,4-Dinitrotoluene (DNT) dioxygenase from Burkholderia sp. strain DNT catalyzes the initial oxidation of DNT to form 4-methyl-5-nitrocatecho l (NNC) and nitrite. The displacement of the aromatic nitro group by d ioxygenases has only recently been described, and nothing is known abo ut the evolutionary origin of the enzyme systems that catalyze these r eactions. We have shown previously that the gene encoding DNT dioxygen ase is localized on a degradative plasmid within a 6,8-kb NsiI DNA fra gment (W.-C. Suen and J. C. Spain, J. Bacteriol, 175:1831-1837, 1993). We describe here the sequence analysts and the substrate range of the enzyme system encoded by this fragment. Five open reading frames were identified, four of which have a high degree of similarity (59 to 78% identity) to the components of naphthalene dioxygenase (NDO) from Pse udomonas strains. The conserved amino acid residues within NDO that ar e involved in cofactor binding were also identified in the gene encodi ng DNT dioxygenase. An Escherichia coli clone that expressed DNT dioxy genase converted DNT to MNC and also converted naphthalene to (+)-cis- (1R,2S)-dihydroxy-1,2-dihydronaphthalene. In contrast, the E. coli clo ne that expressed NDO did not oxidize DNT. Furthermore, the enzyme sys tems exhibit similar broad substrate specificities and can oxidize suc h compounds as indole, indan, indene, phenetole, and acenaphthene. The se results suggest that DNT dioxygenase and the NDO enzyme system shar e a common ancestor.