Biodegradation of Phenanthrene by Rhizobium petrolearium SL-1

Rhizobium petrolearium SL-1 was originally isolated because of its ability to metabolize phenanthrene (PHE) from oil-contaminated soil. Conducting high-performance liquid chromatography (HPLC), UV-visible and gas chromatography-mass spectrometry (GC-MS) analyses, the PHE degrading properties of the strain SL-1 and its metabolites were analysed, and then combined with genomic technology to elucidate the possible metabolic pathways of PHE in R. petrolearium SL-1. PHE (100 mg L-1) was completely degraded by strain SL-1 at 35 ℃, 0.02 % salinity and pH 9.0 within 3 days. A wide range of polycyclic aromatic hydrocarbons (PAHs), including naphthalene, fluorene, anthracene and pyrene, could also be degraded by this strain. On the basis of the identified metabolites, the utilization of probable intermediates and putative phenanthrene catabolic genes, we deduced that PHE was degraded through an initial dioxygenation on 3,4-C, and then the resultant diols from 3,4-dioxygenations was further transformed to 1-hydroxy-2-naphthoic acid. Interestingly, 1-hydroxy-2-naphthoic acid was further degraded via two different routes, namely the ‘naphthalene’ and the ‘phthalic acid’ routes. This phenomenon can probably explain why R. petrolearium SL-1 possesses high PHE biodegradability. Because of its well stress resistance, metabolic versatility, high-efficiency and potential application values in relation to phytoremediation, this bacterium may be proposed as a potential candidate for the bioremediation of PAH-contaminated areas.