SUMMARY: sp. NCIB 9816 contains two plasmids: pWW60, an IncP9 plasmid of 87 kb encoding genes for the catabolism of naphthalene, and pWW61, a cryptic plasmid of about 65 kb. The ability to degrade naphthalene was transferred at low frequency by conjugation from strain NCIB 9816 into a plasmid-free strain of , PaW340. A transconjugant, PaW701, containing the naphthalene plasmid pWW60-1, metabolized naphthalene and salicylate via the pathway. 2-Methylnaphthalene was not a growth substrate but was partly metabolized with accumulation of a brown compound in the medium (λ = 440 nm). Spontaneous mutants of PaW701 with the ability to grow on 2-methylnaphthalene arose at a frequency of about 10. These fell into two groups. Group A mutants had no detectable salicylate hydroxylase activity and accumulated salicylate from naphthalene in culture supernatants: they appeared to grow on the pyruvate released from oxidation of the first ring of both substrates. Their plasmids all contained a 16.7 kb insert in different sites within a small, limited region of the plasmid. Group B mutants used a pathway for catabolism of naphthalene and 2-methylnaphthalene. Their plasmids had undergone a small deletion of from 1.2 to 1.6 kb in a region of the plasmid close to the sites of the insertions in the group A mutants.


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