Three strains of psychrophilic bacteria isolated from Antarctic coastal marine environments were studied to determine their taxonomic position. These bacteria were Gram-negative rods, facultatively anaerobic and motile by means of a single polar flagellum. None of the bacterial isolates had an Na M requirement. Only one of the strains was capable of producing H 2 S from thiosulfate. The DNA base content of these bacteria was 41-42 mol % GMC. DNA-DNA hybridization experiments showed that the isolates formed two related groups that exhibited about 70 and 24 % DNA-DNA homology, respectively, with the type strain of Shewanella frigidimarina. The fatty acid profiles of the bacterial isolates were similar to the profiles of other Shewanella species. All the strains contained both ubiquinones and menaquinones, like Shewanella species. Methylmenaquinones were also found. 16S rRNA gene analysis confirmed that isolated strains belonged to the genus Shewanella and were phylogenetically related to the newly identified Shewanella frigidimarina. The results of the polyphasic taxonomic study assigned the three isolates to Shewanella and two of them specifically to Shewanella frigidimarina.
INTRODUCTIONThe genus Shewanella was first described 14 years ago by MacDonell & Colwell (1985). The definition of Shewanella was based almost entirely on rRNA structure and included only the description ' straight or curved rods, Gram-negative, non-pigmented, motile by polar flagella, chemo-organotrophic, oxidasepositive, generally associated with aquatic or marine habitats. GjC mol % 44-47 '. The species Shewanella putrefaciens (Derby & Hammer, 1931 ; Lee et al., 1977) and Shewanella hanedai (Jensen et al., 1980)
Abbreviation : TMAO, trimethylamine N-oxide.The EMBL accession numbers for the 16S rDNA gene sequence of strains NF12 and NF22 T are AJ300833 and AJ300834, respectively. included in the genus Shewanella, nine of which have been described in the last 3 years. Although the development of this bacterial group, from a taxonomic point of view, has taken place in the last decade, Shewanella putrefaciens has been studied since its first description as Achromobacter putrefaciens by Derby & Hammer (1931), because of its special interest in the areas of applied and environmental microbiology.Shewanella putrefaciens, first isolated as Achromobacter putrefaciens from rancid butter, was classified in 1960 as Pseudomonas putrefaciens by Shewan et al. (1960) and, later, as Alteromonas putrefaciens by Lee et al. (1977). This micro-organism has been found to be associated with the spoilage of proteinaceous foods (Shewan, 1977). Shewanella species are widely distributed and have been isolated from diverse sources such as aquatic environments (Nealson et al., 1991), sediments (Myers & Nealson, 1988), oilfield fluids Nu! ria Bozal and others (Semple & Westlake, 1987) and, as mentioned above, spoilage of proteinaceous foods (Levin, 1972 ;Shewan, 1974 ;Parker & Levin, 1983 ;Stenstrom & Molin, 1990), and are considered opportunistic pathogens...
