Growth of Sphingobium barthaii KK22 on 1-ethylnaphthalene reveals diverse oxidative transformations and a complex metabolite profile

Abstract

Alkylated polycyclic aromatic hydrocarbons (APAHs) are major components of crude oils and petroleum-contaminated sediments and include the relatively water insoluble polyalkyl chain-alkylated PAHs (CA-PAHs). Little is known regarding CA-PAH transformation by microorganisms and therefore biodegradation pathways have not been established. Biotransformation of the CA-PAH 1-ethylnaphthalene (1-EN) by soil bacterium Sphingobium barthaii KK22 was investigated by gas chromatography and comprehensive liquid chromatography electrospray ionization tandem mass spectrometry analyses. 1-EN was utilized as a sole source of carbon and energy by strain KK22 and 200 mg/L of 1-EN as a nonaqueous phase liquid was depleted from culture media in approximately 5 days. 1-EN was oxidized through the aromatic rings, the alkyl moiety and through both the aromatic rings and the alkyl moiety resulting in a diverse metabolite profile that included different carboxylic acid metabolites and conjugation products. Transformation products were organized to construct the first extensive description of 1-EN transformation to the TCA cycle by a bacterium. Key biotransformation products such as 1-naphthoic acid and 3-ethylcatechol were identified and results of independent transformation assays using 1-methylnaphthalene and 1-naphthoic acid confirmed results from 1-EN assays. This work shows that sphingomonads may be versatile contributors to the reduction of CA-PAHs in contaminated environments.