A polycyclic aromatic hydrocarbon-degrading marine bacterium, designated strain P-4 T , was isolated from oil-polluted saline soil in Xianhe, Shangdong Province, China. Strain P-4 T was Gram-negative-staining with curved to spiral rod-shaped cells and grew optimally with 3-6 % (w/v) NaCl and at 30 6C. The predominant fatty acids were C 18 : 1 v7c (35.0 %), C 16 : 0 (25.0 %), C 16 : 1 v7c (17.9 %), C 14 : 0 (6.2 %) and C 17 : 0 cyclo (5.2 %). The major respiratory quinone was Q-9 and the genomic DNA G+C content was 61.2±1.0 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain P-4 T belonged to the genus Thalassospira of the class Alphaproteobacteria. DNA-DNA hybridization with Thalassospira xiamenensis DSM 17429 T showed relatedness of 36.0 %, and lower values were obtained with respect to other Thalassospira species. Based on physiological and biochemical tests and 16S rRNA gene sequence analysis as well as DNA-DNA relatedness, strain P-4 T should be placed in the genus Thalassospira within a novel species. The name Thalassospira xianhensis sp. nov. is proposed, with P-4 T (5CGMCC 1.6849 T 5JCM 14850 T ) as the type strain.Polycyclic aromatic hydrocarbons (PAHs) are hydrocarbons that consist of two or more fused aromatic rings (Habe & Omori, 2003;Hedlund & Staley, 2001). PAHs are released into the marine environment as a result of various anthropogenic activities such as marine seepage and accidental discharges during the transport and disposal of petroleum products and the use of fossil fuels (Sohn et al., 2004). Some PAHs are highly carcinogenic, genotoxic and cytotoxic to marine organisms and may be transferred to humans through seafood consumption (Menzie et al., 1992). Therefore, removal of PAHs from contaminated marine environments is of considerable importance.Several PAH-degrading strains have been isolated from PAH-contaminated marine sediments (Hedlund & Staley, 2001;Kwon et al., 2005;Sohn et al., 2004). In this study, we report the characterization of a PAH-degrading marine bacterium that was isolated from saline soil contaminated with crude oil in Xianhe, Shangdong Province, China.To isolate PAH-degrading bacteria, 5 % sea-salt defined medium (5 % SSDM; Zhao et al., 2009) and 5 % SSDM with 0.5 % yeast extract (5 % SSDMY) were used. Solid 5 % SSDMY medium was prepared with 1.5 % agar. A sample of oil-polluted saline soil (1 g) was added to 100 ml 5 % SSDM medium supplemented with phenanthrene (100 mg ml 21 ) in a 300 ml Erlenmeyer flask. The culture was aerobically incubated at 30 u C in darkness on a rotary shaker operating at 200 r.p.m. After 2 weeks, 10 ml culture was transferred to 100 ml 5 % SSDM medium and incubated under the conditions described above. The enrichment was performed five or six times. Next, a culture broth dilution series was spread on 5 % SSDMY agar. After incubation for 2 days, single colonies were picked and cultivated in 5 ml 5 % SSDM using phenanthrene as the sole source of carbon and energy. These isolates developed a yellowish-orange or red...