Four freshwater Antarctic lakes were examined for the presence of β-galactosidase-producing bacteria using mineral medium enrichments and lactose. Enrichments from only one of the lakes produced growth and two strains were isolated that were very similar in phenotype and fatty acid profile, and shared considerable homology in their DNA (DNA-DNA hybridization = 93±7%). The strains were psychrotrophic with theoretical and of 30–31, -7 ° and 26 °C respectively. The β-galactosidase in cell extracts had an optimal activity at 39 °C. The strains were Gram-negative rods, showed gliding motility, contained branched and hydroxy fatty acids, and menaquinone 6 as the major respiratory quinone. The strains did not form microcysts and utilized lactose while using ammonium ions as a source of nitrogen, and a range of other sugars. The G+C content of the DNA was 34 mol%. Phylogenetic analysis of one of the strains, by comparison of 16S rDNA sequences, showed that it was most similar, but not identical to, and ‘[] ’. Both species could be differentiated phenotypically from the Antarctic isolates. DNA-DNA hybridization of the Antarctic isolate with six different members of the 16S rDNA-cluster showed no strain with greater than 18% relatedness. The nearest type species to the Antarctic isolate in the phylogenetic analysis was The name is proposed for the Antarctic strains, and the type strain is ATCC 51468(= ACAM 376).


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