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J. Biol. Chem., Vol. 280, Issue 16, 15526-15533, April 22, 2005

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A Novel Metabolic Pathway for Degradation of 4-Nonylphenol Environmental Contaminants by Sphingomonas xenophaga Bayram

ipso-HYDROXYLATION AND INTRAMOLECULAR REARRANGEMENT^*

Frédéric L. P. Gabriel, Andy Heidlberger, Daniel Rentsch, Walter Giger, Klaus Guenther¶, and Hans-Peter E. Kohler||

From the Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH-8600 Dübendorf, Switzerland, Materials Science and Technology (EMPA), CH-8600 Dübendorf, Germany, and the ^¶Institute for Chemistry, Instrumental Analytical Chemistry, Duisburg-Essen University, Lotharstrasse 1, D-47048 Duisburg, Germany

Several nonylphenol isomers with -quaternary carbon atoms serve as growth substrates for Sphingomonas xenophaga Bayram, whereas isomers containing hydrogen atoms at the -carbon do not (Gabriel, F. L. P., Giger, W., Guenther, K., and Kohler, H.-P. E. (2005) Appl. Environ. Microbiol. 71, 1123–1129). 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 -carbon atom prevented stabilization of the putative -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 -branched alkyl moieties of alkylphenols for utilization of the aromatic part as a carbon and energy source.

Received for publication, November 30, 2004 , and in revised form, January 19, 2005.

^* This work was supported by the Swiss National Science Foundation (Project PHEBRO 4050-066566) within the framework of the National Research Program NRP50 on "Endocrine Disruptors: Relevance to Humans, Animals, and Ecosystems." The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^|| To whom correspondence should be addressed: EAWAG, Mailbox 611, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland. Tel.: 41-1-8235521; Fax: 41-1-8235547; E-mail: kohler{at}eawag.ch.

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