Exiguobacterium undae sp nov and Exiguobacterium antarcticum sp nov.

Four orange-pigmented strains from pond water (L1-L4) have been subjected to polyphasic taxonomic analyses. On the basis of ribotype analysis and Fourier-transform infrared spectroscopy, these strains form a genomically highly related group. 16S rDNA sequence analysis revealed 98.8% similarity between the 16S rDNA sequences of strains L2(T) and H2(T), isolated previously from a microbial mat from Lake Fryxell, Antarctica. DNA-DNA reassociation values indicated the presence of two genomic clusters. While the DNA of strains L2(T) and L3 showed 100% DNA relatedness, strains L2(T) and H2(T) shared only 51% DNA relatedness. These two clusters differed in some phenotypic properties, e.g. utilization of melibiose, D-mannitol, adenosine 5'-monophosphate and uridine 5'-monophosphate, and in their fatty acid compositions. Based on the composition of isoprenoid quinones, peptidoglycan, polar lipids and fatty acids, these organisms are members of the genus Exiguobacterium. This is supported by 16S rDNA analyses, which revealed 97-98% similarity to Exiguobacterium acetylicum DSM 20416(T) and 93.2-93.8% similarity to Exiguobacterium aurantiacum DSM 6208(T). E. acetylicum DSM 20416(T), the closest phylogenetic neighbour, shows only 39% DNA similarity to strain L2(T) and 40% DNA similarity to strain H2(T). Based on genomic distinctiveness and the clear differences in chemotaxonomy and physiology, two novel species are proposed, Exiguobacterium undae sp. nov. and Exiguobacterium antarcticum sp. nov.