Psychrophilic, yellow-pigmented, seawater-requiring bacteria isolated from the pycnocline of meromictic Burton Lake and from sea ice cores obtained in the Vestfold Hills (68°S, 78°E) in eastern Antarctica were characterized. Phenotypic analysis showed that the strains isolated formed two distinct taxa. The first taxon included nonmotile, nutritionally fastidious strains that were isolated from the pycnocline of Burton Lake. The cells of these strains were morphologically variant, ranging from vibrioid to ring shaped to coiled and filamentous; in addition, the strains were unable to metabolize carbohydrates or polysaccharides and had DNA G+C contents of 27 to 29 mol%. The strains of the second taxon, which were isolated from sea ice cores and from ice algal biomass, were saccharolytic, exhibited rapid gliding motility, were rodlike to filamentous, and had DNA G+C contents of 36 to 38 mol%. A 16S ribosomal DNA (rDNA) sequence analysis revealed that the two Antarctic taxa formed related but distinct lineages within the [] rRNA branch of the family . The levels of 16S rDNA sequence similarity between the taxa were 90.5 to 91.3%, while the levels of similarity to other members of the [] rRNA branch were 85 to 90%. The whole-cell lipid profiles of the Antarctic strains were mainly comprised of branched and unbranched monounsaturated Cto Cfatty acids. The presence of significant levels of the lipids a15:1 ω 10c and a17:1 ω 7c appeared to be useful biomarkers for the new Antarctic taxa and for differentiating these organisms from other members of the family . On the basis of polyphasic taxonomic data we propose that the new taxa are novel bacterial species designated gen. nov., sp. nov. (type strain, ACAM 188) and gen. nov., sp. nov. (type strain, ACAM 536).


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