Structure-toxicity assessment of metabolites of the aerobic bacterial transformation of substituted naphthalenes

Pseudomonas fluorescens 5R, a naphthalene-degrading bacterium isolated from manufactured gas plant soil contaminated with polycyclic aromatic hydrocar bons, was examined for its degradative capacity of a number of substituted naphthalenes. In general, those compounds substituted on only one ring with an electrically neutral substituent were found to be transformed primarily to substituted salicylic acids according to the classical (NAH7) naphthale ne dioxygenase-initiated upper pathway reactions of the naphthalene degrada tive pathway (i.e., the NAH system). Dimethylnaphthalenes with a substituen t on each ring, and certain halogenated naphthalenes, were transformed via a monohydroxylation reaction to form hydroxylated dead-end products. Of the substituted salicylic acids examined, only 3- and 4-methylsalicylic acid, the respective products of the degradation of 1- and 2-methylnaphthale ne, were further degraded by salicylate hydroxylase and catechol 2,3-dioxygenas e, the first two enzymes of the NAH lower pathway. Using the Tetrahymena py riformis acute toxicity assay, many of the monohydroxylated products of inc omplete biodegradation were found to be polar narcotics. Substituted salicy lic acids that are not further degraded by the NAH lower pathway were found to be toxic via carboxylic acid narcosis.