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

Abstract

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. 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 ipsoposition 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.

Novel Metabolic Pathways of p-n-Nonylphenol Catalyzed by Cytochrome P450 and Estrogen Receptor Binding Activity of New Metabolites

“…The above results indicate that p-nonylphenol was metabolized by ipso-addition to nonylquinol by rat or human liver microsomal P450. This compound has been reported to be a metabolite of nonylphenol in bacteria, 11) but has not been reported to be a metabolite in humans or animals.…”

Changes of catabolic genes and microbial community structures during biodegradation of nonylphenol ethoxylates and nonylphenol in natural water microcosms

“…It has been reported that NP could be degraded with fission of the phenol ring by some isolated strains, and it seems to be able to further degrade the aromatic moiety of NP isomers as growth substrates [30,31] proved the existence of a novel pathway that enables bacteria to detach the alkyl substituent of an NP isomer as C9 alcohol and to utilize the ring as a source of carbon and energy. As for NPEOs, it is reported that ultimate biodegradation of the metabolites occurs more slowly, if at all, because of the need for a specific enzyme or bacterial population [32].…”

Cyclodextrin-linked alginate beads as supporting materials for Sphingomonas cloacae, a nonylphenol degrading bacteria

“…Although nonylphenol is recalcitrant in nature, its bioavailability has triggered extensive studies on its bio-remediation by use of some yeast and gram-negative bacteria. Candida aquaetexotoris was reported to decompose the alkyl chain of nonylphenol to give 4-acetylphenol (Vallini et al, 2001), while several bacteria such as Sphingomonas xenophaga (Gabriel et al, 2005), Sphingomonas cloacae (Fuji et al, 2000), and Sphingobium amiense (Ushiba et al, 2003) metabolized its aromatic moiety to the corresponding C9 alcohols.…”