Biodegradation of phenanthrene by Rhizobium petrolearium SL-1

Aims: We aimed to investigate the phenanthrene degradation characteristics and possible phenanthrene degradation pathways of Rhizobium petrolearium SL-1. Methods and Results: Using high-performance liquid chromatography (HPLC), UV-visible and gas chromatography-mass spectrometry (GC-MS) analysis, the phenanthrene-degrading properties and metabolites of Rh. petrolearium SL-1 were analysed, and then combined with genome-based analysis to elucidate the possible biodegradation pathway of phenanthrene in Rh. petrolearium SL-1. The results of the analyses showed that phenanthrene (100 mg l(-1)) was completely degraded by strain SL-1 at 35 degrees C, 0.02% salinity and pH 9.0 within 3 days. A wide range of polycyclic aromatic hydrocarbons, including naphthalene, fluorene, anthracene and pyrene, could also be degraded by this strain. Conclusions: Based on the identified metabolites, the utilization of probable intermediates and the presence of putative phenanthrene catabolic genes, we concluded that phenanthrene was degraded via two different routes, namely the 'naphthalene' and the 'phthalic acid' routes. Significance and Impact of the Study: For the first time, this study shows the degradation pathway of phenanthrene by a Rhizobium strain. Because of its excellent stress resistance, metabolic versatility, high degradation efficiency and potential application in phytoremediation, Rh. petrolearium SL-1 is a potential candidate for the bioremediation of polycyclic aromatic hydrocarbons-contaminated areas.