Thirty-one bacteria that belonged to the genus Pseudomonas were isolated from cyanobacterial mat samples that were collected from various water bodies in Antarctica. All 31 isolates were psychrophilic; they could be divided into three groups, based on their protein profiles. Representative strains of each of the three groups, namely CMS 35T, CMS 38T and CMS 64T, were studied in detail. Based on 16S rRNA gene sequence analysis, it was established that the strains were related closely to the Pseudomonas fluorescens group. Phenotypic and chemotaxonomic characteristics further confirmed their affiliation to this group. The three strains could also be differentiated from each other and the closely related species Pseudomonas orientalis, Pseudomonas brenneri and Pseudomonas migulae, based on phenotypic and chemotaxonomic characteristics and the level of DNA–DNA hybridization. Therefore, it is proposed that strains CMS 35T (=MTCC 4992T=DSM 15318T), CMS 38T (=MTCC 4993T=DSM 15319T) and CMS 64T (=MTCC 4994T=DSM 15321T) should be assigned to novel species of the genus Pseudomonas as Pseudomonas antarctica sp. nov., Pseudomonas meridiana sp. nov. and Pseudomonas proteolytica sp. nov., respectively.

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CMS 19YT , a psychrophilic bacterium, was isolated from a cyanobacterial mat sample from a pond in Antarctica and was characterized taxonomically. The bacterium was aerobic, Gram-positive, non-spore-forming, non-motile, exhibited a rod-coccus growth cycle and produced a yellow pigment that was insoluble in water but soluble in methanol. No growth factors were required and it was able to grow between 5 and 30 SC, between pH 6 and pH 9 and tolerated up to 115 % NaCl. The cell wall peptidoglycan was Lys-Thr-Ala3 (the A3α variant) and the major menaquinone was MK-9(H 2 ). The GMC content of the DNA was 64O2 mol %. The 16S rDNA analysis indicated that CMS 19YT is closely related to group I Arthrobacter species and showed highest sequence similarity (9791 %) with Arthrobacter agilis. Furthermore, DNA-DNA hybridization studies also indicated 77 % homology between CMS 19Y T and A. agilis. It differed from A. agilis, however, in that it was psychrophilic, nonmotile, yellow in colour, exhibited a rod-coccus growth cycle, had a higher degree of tolerance to NaCl and was oxidase-and urease-negative and lipasepositive. In addition, it had a distinct fatty acid composition compared to that of A. agilis : the predominant fatty acids were C

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