The taxomony of strain CRSS (DSM 15686(T)=ATCC BAA-848(T)) isolated from Cape Russell in Antarctica (Ross Sea, 74 52.35 S 163 53.03 E) was investigated in a polyphasic approach. The morphological, physiological and genetic characteristics were compared with that of related species of the genus Halomonas. The isolate grew optimally at pH 9.0, 10% NaCl at 30 degrees C. The cells were Gram-negative aerobic rods able to produce exopolysaccharide. They accumulated glycine-betaine, as a major osmolyte, with minor components ectoine and glutamate. The strain CRSS biosynthetised alpha-glucosidase. The polar lipid profile consisted of phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol as major components. Ubiquinone with nine repetitive unities (Q9) was the only quinone found and the fatty acid composition was dominated by C18:1 (53%). The G+C content of DNA was 55.0mol% and its phylogenetic position was established by 16S rRNA gene sequencing as a member of the genus Halomonas. For physiological, chemotaxonomic and genetic features (DNA-DNA hybridisation) it is proposed to classify the isolate as a new species for which we propose the name Halomonas alkaliantarctica sp. nov.