A bacterial strain,CN-3,was isolated from the petroleum-contaminated sediments in Bohai Bay,China.Morphological,physiological and phylogenetic analyses indicated that the strain belonged to the genus Dietzia.It was capable of utilizing alkanes,aromatic compounds and crude oil as the sole carbon sources for growth.The degradation efficiency of petroleum hydrocarbons were detected by using GC-MS analyses.The strain CN-3 could degrade 82%of saturated hydrocarbons fraction of crude oil at a petroleum initial concentration of 5 g/L in 14 days.Various experiments were conducted to investigate the effect of pH and salinity on the degradation efficiency of petroleum.The results indicated that the strain CN-3 had the better degradation effect on the crude oil in the slightly alkaline condition and the degradation activities were not affected significantly when the NaCl concenwation reached 85 g/L.Based on the mechanism,the alkB(coding for alkane monooxygenase)and CYP153(coding for P450 alkane hydroxylase of the cytochrome CYP153family)genes were detected,which explained the high biodegradation ofDietzia sp.CN-3 to the alkanes.