J. Gen. Appl. Microbiol., 51, 385–394 (2005)

from an amphipod sample by Yayanos et al. (1979), piezophilic bacteria have been isolated from various depths (Deming, 1985; Deming et al., 1988; Jannasch and Wirsen, 1984; Jannasch et al., 1982; Kato et al., 1995; Nakayama et al., 1994; Yayanos et al., 1981, 1982). Almost all piezophilic bacteria were isolated from samples of deep-sea water, sediment, or amphipods. Most of them were classified under the Proteobacteria g-subgroup according to phylogenetic analyses based on 16S rRNA gene sequences (DeLong et al., 1997; Kato et al., 1996, 1998; Nogi and Kato, 1999; Nogi et al., 1998a, b, c). Unlike the other researchers studying deep-sea piezophilic bacteria, we isolated deep-sea piezophilic bacteria from the intestinal contents of deep-sea fishes (Coryphaenoides yaquinae, Coryphaenoides armatus, and Ilyophis sp.) retrieved from depths of 3,100 m to 6,100 m using crab pot fishing during surveys of R/V Soyo Maru in the Northwest Pacific Ocean (Nakayama et al., 1994; Yano et al., 1995, 1997). Compared with deep-sea water and sediment samples, the intestines of deep-sea fishes are specific and exceptional habitats with an abundance of organic matter in the deepsea environments. Therefore, in this study to compare between bacteria in intestines of deep-sea fishes and ones from deep-sea water and sediment samples, we carried out phylogenetic analysis of our deep-sea piezophilic bacteria based on nucleotide sequences of 16S rRNA gene. Moreover, we examined the relationship between the depths from which the samples were retrieved and the piezophilism of the bacteria isolated from them. Deep-sea fishes (Coryphaenoides yaquinae, Coryphaenoides armatus, and Ilyophis sp.) were retrieved from depths of 3,100 m to 6,100 m at 10 stations in the northwestern Pacific Ocean in 1989, 1990, 1991, and 1992 by the R/V Soyo Maru’s crab pot fishing as reported previously (Nakayama et al., 1994; Yano et al., 1995, 1997). The sampling method of the intestines from these deep-sea fishes and the isolation of deep-sea bacteria from these intestinal contents Phylogenetic analysis based on 16S rRNA gene sequences of deep-sea bacteria isolated from intestinal contents of deep-sea fishes retrieved from the abyssal zone