A novel metabolic pathway for degradation of 4-nonylphenol environmental contaminants by Sphingomonas xenophaga Bayram

Gabriel, F.; Giger, W.; Günther, K.; Rentsch, D.; Kohler, H.-P.; Heidelberger, A.

doi:10.1074/jbc.M413446200

Journal Article

A novel metabolic pathway for degradation of 4-nonylphenol environmental contaminants by Sphingomonas xenophaga Bayram

Gabriel, F. ; Heidelberger, A. ; Rentsch, D. ; Giger, W. ; Günther, K.FZJ* ; Kohler, H.-P.

2005
Soc. Bethesda, Md.

The journal of biological chemistry 280, 15526 - 15533 (2005) [10.1074/jbc.M413446200]

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Please use a persistent id in citations: http://hdl.handle.net/2128/2668 doi:10.1074/jbc.M413446200

Abstract: Several nonylphenol isomers with alpha-quaternary carbon atoms serve as growth substrates for Sphingomonas xenophaga Bayram, whereas isomers containing hydrogen atoms at the alpha-carbon do not. Three metabolites of 4-(1-methyloctyl)-phenol were isolated in mg quantities from cultures of strain Bayram supplemented with the growth substrate isomer 4-(1-ethyl-1,4-dimethyl-pentyl)-phenol. They were unequivocally identified as 4-hydroxy-4-(1-methyl-octyl)-cyclohexa-2,5-dienone, 4-hydroxy-4-(1-methyl-octyl)-cyclohex-2-enone, and 2-(1-methyl-octyl)-benzene-1,4-diol by high pressure liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. Furthermore, two metabolites originating from 4-n-nonylphenol were identified as 4-hydroxy-4-nonyl-cyclohexa-2,5-dienone and 4-hydroxy-4-nonyl-cyclohex-2-enone by high pressure liquid chromatography-mass spectrometry. We conclude that nonylphenols were initially hydroxylated at the ipso-position forming 4-alkyl-4-hydroxy-cyclohexa-2,5-dienones. Dienones originating from growth substrate nonylphenol isomers underwent a rearrangement that involved a 1,2-C,O shift of the alkyl moiety as a cation to the oxygen atom of the geminal hydroxy group yielding 4-alkoxyphenols, from which the alkyl moieties can be easily detached as alcohols by known mechanisms. Dienones originating from nongrowth substrates did not undergo such a rearrangement because the missing alkyl substituents at the alpha-carbon atom prevented stabilization of the putative alpha-carbocation. Instead they accumulated and subsequently underwent side reactions, such as 1,2-C,C shifts and dihydrogenations. The ipso-hydroxylation and the proposed 1,2-C,O shift constitute key steps in a novel pathway that enables bacteria to detach alpha-branched alkyl moieties of alkylphenols for utilization of the aromatic part as a carbon and energy source.

Keyword(s): Carbon Isotopes (MeSH) ; Carbon Radioisotopes (MeSH) ; Environmental Pollutants: metabolism (MeSH) ; Isomerism (MeSH) ; Magnetic Resonance Spectroscopy (MeSH) ; Mass Spectrometry (MeSH) ; Phenols: metabolism (MeSH) ; Sphingomonas: metabolism (MeSH) ; Time Factors (MeSH) ; Carbon Isotopes ; Carbon Radioisotopes ; Environmental Pollutants ; Phenols ; 4-nonylphenol ; J