Two Gram-negative, strictly aerobic bacterial strains, designated CL-AP6(T) and CL-AP22, were isolated from a culture of a green alga, Pyramimonas gelidicola, established from the Antarctic. Cells of the strains were straight rods and motile by means of a single polar flagellum. The strains grew with 0.5-8 % (w/v) NaCl (optimum, 1-2 %) and at 4-33 degrees C (optimum, 25 degrees C) and pH 6.5-9.1 (optimum, pH 7.5-8.1). The two strains shared 98.8 % 16S rRNA gene sequence similarity. Analysis of the 16S rRNA gene sequences of strains CL-AP6(T) and CL-AP22 revealed that they were members of the genus Pseudomonas and were most closely related to Pseudomonas xiamenensis C10-2(T) (95.5-95.8 % sequence similarity) and next to Pseudomonas pertucinogena NBRC 14163(T) (95.1-95.5 % sequence similarity) and to other members of the genus Pseudomonas (<95.2 % sequence similarity). Phylogenetic analyses based on the 16S rRNA gene sequences showed that strain CL-AP6(T) formed a robust clade with strain CL-AP22, and that this clade clustered tightly with the nearest clade containing P. xiamenensis and P. pertucinogena. The major isoprenoid quinone of strains CL-AP6(T) and CL-AP22 was Q-9 and the major cellular fatty acids were C(18 : 1)omega7c (40.2-41.6 %), summed feature 3 (C(16 : 1)omega7c and/or iso-C(15 : 0) 2-OH; 26.3-26.8 %), C(16 : 0) (13.7-13.9 %) and C(12 : 0) (5.8-6.2 %). The genomic DNA G+C contents of strains CL-AP6(T) and CL-AP22 were 59.1 and 57.2 mol%, respectively. DNA-DNA hybridization experiments revealed high relatedness values (98.5+/-0.5 %; mean+/-sem, n=2) between strains CL-AP6(T) and CL-AP22, indicating that the two strains constituted a single species. However, the two strains differed phenotypically from P. xiamenensis by their inability to grow without NaCl, temperature range for growth, hydrolysis of starch and production of certain enzymes. The phylogenetic analysis and physiological and biochemical data showed that strains CL-AP6(T) and CL-AP22 should be classified as representing a novel species in the genus Pseudomonas, for which the name Pseudomonas pelagia sp. nov. is proposed. The type strain is CL-AP6(T) (=KCCM 90073(T)=JCM 15562(T)).