Elucidation of the metabolic pathway of fluorene and cometabolic pathways of phenanthrene, fluoranthene, anthracene and dibenzothiophene by Sphingomonas sp. LB126

Abstract

The metabolic pathway of the PAH fluorene and the cometabolic pathway of the PAHs phenanthrene, fluoranthene, anthracene and dibenzothiophene in Sphingomonas sp. LB126 were examined. To our knowledge this is the first study on the cometabolic degradation of the three-ring PAHs phenanthrene, anthracene and the four-ring PAH fluoranthene by a fluorene-utilizing species. Metabolism of fluorene was shown to proceed via the 9-fluorenone pathway to form o-phthalic acid and protocatechuic acid. The cometabolic mono-hydroxylation found for phenanthrene, fluoranthene and anthracene shows similarity with the hydroxylation of fluorene. Several mono- and dihydroxy products and ring-cleavage products were identified for phenanthrene, fluoranthene and anthracene. It appeared that the cometabolism of those three compounds is a non-specific process, in contrast to the metabolism of fluorene. For dibenzothiophene the metabolites dibenzothiophene-5-oxide and dibenzothiophene-5,5-dioxide were identified; these compounds appeared to be the products of a dead-end pathway. Since apart from dibenzothiophene no metabolites were found in very high concentrations for any of the other substrates, complete degradation is suggested, even for the cometabolic degradation of phenanthrene, fluoranthene and anthracene.