A versatile bacterial strain able to convert polycyclic aromatic hydrocarbons (PAHs) was isolated, and a conversion by the isolate of both individual substances and PAH mixtures was investigated. The strain belonged to the Sphingomonas genus as determined on the basis of 16S rRNA analysis and was designated as VKM B-2434. The strain used naphthalene, acenaphthene, phenanthrene, anthracene and fluoranthene as a sole source of carbon and energy, and cometabolically oxidized fluorene, pyrene, benz[a]anthracene, chrysene and benzo[a]pyrene. Acenaphthene and fluoranthene were degraded by the strain via naphthalene-1,8-dicarboxylic acid and 3-hydroxyphthalic acid. Conversion of most other PAHs was confined to the cleavage of only one aromatic ring. The major oxidation products of naphthalene, phenanthrene, anthracene, chrysene, and benzo[a]pyrene were identified as salicylic acid, 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, o-hydroxyphenanthroic acid and o-hydroxypyrenoic acid, respectively. Fluorene and pyrene were oxidized mainly to hydroxyfluorenone and dihydroxydihydropyrene, respectively. Oxidation of phenanthrene and anthracene to the corresponding hydroxynaphthoic acids occurred quantitatively. The strain converted phenanthrene, anthracene, fluoranthene and carbazole of coal-tar-pitch extract.

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The biodegradation of the polycyclic aromatic hydrocarbon phenantherene by the rhizobacterial strain Ensifer meliloti P221, isolated from the root zone of plant grown in PAH-contaminated soil was studied. Bacterial growth and phenanthrene degradation under the influence of root-exuded organic acids were also investigated. Analysis of the metabolites produced by the strain by using thin-layer chromatography, gas chromatography, high-pressure liquid chromatography, and mass-spectrometry revealed that phenanthrene is bioconverted via two parallel pathways. The first, major pathway is through terminal aromatic ring cleavage (presumably at the C3-C4 bond) producing benzocoumarin and 1-hydroxy-2-naphthoic acid, whose further degradation with the formation of salicylic acid is difficult or is very slow. The second pathway is through the oxidation of the central aromatic ring at the C9-C10 bond, producing 9,10-dihydro-9,10-dihydroxyphenanthrene, 9,10-phenanthrenequinone, and 2,2'-diphenic acid. This is the first time that the dioxygenation of phenanthrene at the C9 and C10 atoms, proven by identification of characteristic metabolites, has been reported for a bacterium of the Ensifer genus.

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