Evidence of two metabolic pathways for degradation of 2-methylphenanthrene by Sphingomonas sp strain (2MPII)

A pure bacterial strain of Sphingomonas sp. DSM 11572 (named 2MPII) has been isolated from a Mediterranean coastal sediment. This strain is able to use 2-methylphenanthrene (2-MP) as a growth substrate. In order to understand the degradation processes and their selectivity, we have elucidated the metabolic pathways of 2-MP degradation. In this respect, in this paper, we report the identification of several metabolites resulting from the oxidation of 2-MP by the Sphingomonas sp. Metabolites of 2-MP, identified by gas chromatography coupled to mass spectrometry in culture media, belong to two distinct metabolic pathways. The first pathway involves, in the first step, the double hydroxylation of an aromatic ring catalyzed by a di-oxygenase. This pathway generates before the opening of the aromatic ring. The exact double hydroxylation positions have not been totally elucidated. The second pathway is initiated by the hydroxylation of the methyl side chain by a mono-oxygenase. It leads, by the oxidation of the methyl group, to the formation of alcohol, aldehyde, and carboxylic acid.