Characterization of facultative oligotrophic bacteria from polar seas by analysis of their fatty acids and 16S rDNA sequences

One hundred and seventy three bacterial strains, isolated previously after enrichment under oligotrophic, psychrophylic conditions from Arctic (98 str ains) and Antarctic seawater (75 strains), were characterized by gas-liquid chromatographic analysis of their fatty acid compositions. By numerical an alysis, 8 clusters, containing 2 to 59 strains, could be delineated, and 8 strains formed separate branches. Five clusters contained strains from both poles, two minor clusters were confined cc Arctic isolates, and one cluste r consisted of Antarctic isolates only. The 16S rRNA genes from 23 strains, representing the different fatty acid profile clusters and including the u nclustered strains, were sequenced. The sequences grouped with the alpha an d gamma Proteobacteria, the high percent G+C Gram positives, and the Cytoph aga-Flavobacterium-Bacteroides branch. The sequences of strains from 4 clus ters and of 7 unclustered strains were closely related (sequence similariti es above 97%) to reference sequences of Sulfitobacter mediterraneus, Halomo nas variabilis, Alteromonas mncleodii, Pseudoalteromonas species, Shewanell a frigidimarina, and Rhodococcus fascians. Strains from the other four clus ters and an unclustered strain showed sequence similarities below 97% with nearest named neighbours, including Rhizobium, Glaciecola, Pseudomonas, Alt eromonas macleodii and Cytophaga marinoflava, indicating that the clusters which they represent form as yet unnamed rare.