Taxonomic Studies of Deep-sea Barophilic Bacteria
Yuichi NOGI*, Chiaki KATO, and Koki HORIKOSHI
The DEEPSTAR group, Japan Marine Science and Technology Center, 2-15 Natsushima-cho, Yokosuka 237, Japan
Numerous deep-sea barophilic bacterial strains have been isolated and characterized since the 1979 report by Yayanos et al. (1), in an effort to understand the interaction between the deep-sea environment and its microbial inhabitants. Barophilic bacteria are characterized by enhanced growth at pressures above 1 atmosphere. Thus far, all barophilic bacterial isolates fall into the Proteobacteria γ-subgroup according to phylogenetic classifications derived from 16S ribosomal RNA sequence information by Kato et al. (2), and the cultivated psychrophilic and barophilic deep-sea bacteria are affiliated with one of five genera within the γ-subgroup: Shewanella, Photobacterium, Colwellia, Moritella, and a new group reported by DeLong et al. (3). The deep-sea adapted type species of three of these genera were previously reported as S. benthica in the genus Shewanella, C. hadaliensis in the genus Colwellia, and M. marinus in the genus Moritella. In this study, we identified four new species of barophilic and barotolerant bacteria belonging to the genera Shewanella, Moritella and Photobacterium from our collections. We proposed the deep-sea type species of genus Photobacterium as P. profundum (4).
We have isolated several deep-sea adapted barophilic and barotolerant bacteria in the genera Photobacterium, Shewanella and Moritella. Members of these genera are common bacteria in marine environments. Although the 16S rRNA sequences of these isolates have been determined, additional information relating to their taxonomic placements with the related bacteria are needed. Because these genera must be the dominant cultivatable benthic bacterial groups, their taxonomic characterizations are an important component of the characterization of deep-sea microbial populations. We describe the properties of the isolated strains from deep-sea sediment samples, several lines of evidence indicate that some of isolates, DSJ4, DSS12, and DSK1, and DB21MT-5, are members of the genera, Photobacterium, Shewanella, and Moritella, respectively, and are new species. These new species of bacteria are particularly adapted to the deep-sea environment, and are barotolerant (strain DSK1), moderately barophilic (strains DSJ4 and DSS12), and hyperbarophilic (strain DB21MT-5). Their temperature ranges for growth and cell fatty acid components partially differ from those of known species, and compared with closely related type strains there was only a low level of DNA similarity. Based on these differences, the description of strain DSJ4 as a new deep-sea species, Photobacterium profunclum (JCM 10084) is
