Data are presented indicating that the major pathway for the oxidation of naphthalene by a strain of Pseudomonas occurs via salicylic acid, which is further oxidized through catechol to β-ketoadipic acid. On the basis of growth, simultaneous adaptation, and cell-free extract experiments, the following compounds are regarded as unlikely intermediates in naphthalene dissimilation: 1,4-naphthoquinone, α-naphthol, β-naphthol, 1,3-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 1,5-dihydroxynaphthaIene, phenol, trans-o-hydroxycinnamic acid, and phthalic acid. Evidence was found that a second pathway of naphthalene oxidation produces 1,2-naphthoquinone. 1,2-Dihydroxynaphthalene was found to be non-enzymatically converted to 1,2-naphthoquinone. The 1,2-naphthoquinone was not further metabolized and was found to be responsible for the characteristic brown to reddish orange color of the culture medium. Omission of FeCl2and MgSO4from the basal medium prevented the formation of salicylic acid but did not interfere with the production of 1,2-naphthoquinone.
