OXIDATION OF METHYL-SUBSTITUTED NAPHTHALENES - PATHWAYS IN A VERSATILE SPHINGOMONAS-PAUCIMOBILIS STRAIN

Aromatic compounds with alkyl substituents are abundant in fossil fuel s. These compounds become important environmental sources of soluble t oxic products, developmental inhibitors, etc, principally through biol ogical activities. To assess the effect of methyl substitution on the completeness of mineralization and accumulation of pathway products, a n isolate from a phenanthrene enrichment culture, Sphingomonas paucimo bilis 2322, was used. Washed cell suspensions containing cells grown o n 2,6-dimethylnaphthalene in mineral medium were incubated with variou s mono-, di-, and trimethylnaphthalene isomers, and the products were identified and quantified by gas chromatography and mass spectrometry. The data revealed enzymes with relaxed substrate specificity that ini tiate metabolism either by methyl group monoxygenation or by ring diox ygenation. Congeners with a methyl group on each ring initially hydrox ylate a methyl, and this is followed by conversion to a carboxyl; when there are two methyl groups on a single ring, the first reaction is a ryl dioxygenation of the unsubstituted ring. Intermediates are channel ed to primary ring fission via dihydrodiols to form methyl-substituted salicylates. Further evidence that there are multiple pathways comes from the fact that both phthalate and (methyl)salicylate are formed fr om 2-methylnaphthalene.