Metabolism of 3-methyldiphenyl ether by Sphingomonas sp. SS31

The bacterium Sphingomonas sp. SS31, which was obtained from the diphenyl ether-degrading strain Sphingomonas sp. SS3 by an adaptation process, utilized 3-methyldiphenyl ether for growth in addition to diphenyl ether. The initial enzymatic attack onto this compound proceeded by a regioselective, but non-specific dioxygenation at the carbon carrying the ether bridge and the adjacent carbon of the unsubstituted as well as the methyl-substituted aromatic nucleus. Upon spontaneous decomposition, the resulting unstable hemiacetal structure yielded 3-methylphenol and catechol, or phenol, 3-methylcatechol, and 4-methylcatechol, respectively. Phenol and 3-methylphenol methylphenol were oxidized to the corresponding catechols which, after subsequent ortho-cleavage, were channeled into the oxoadipate pathway. Minor amounts of 3-(hydroxymethyl)-diphenyl ether detected in the supernatant of the culture broth gave evidence for an unproductive oxidation of the side-chain, finally leading to the nondegradble product 3-carboxydiphenyl ether.