Reclassification of salt-water Bdellovibrio sp as Bacteriovorax marinus sp nov and Bacteriovorax litoralis sp nov.

Bdellovibrios are unique, predatory bacteria with an intraperiplasmic growth and multiplication phase within their prey, which consists of many Gram-negative bacteria. Until recently, all bacteria that exhibited these traits were included in the genus Bdellovibrio. However, analysis of 16S rDNA sequences and other studies have demonstrated substantial genotypic, phenotypic and ecotypic diversity among the organisms in this genus (Baer et al., 2000; Snyder et al., 2002). This has resulted in reclassification of Bdellovibrio stolpii and Bdellovibrio starrii into the newly constructed genus Bacteriovorax (Baer et al., 2000). In this study, examination of marine isolates of Bdellovibrio (designated SJ(T), AQ and JS5(T)) has revealed them to be related more closely to the newly designated genus Bacteriovorax. Phylogenetic analysis of 16S rRNA gene sequences revealed that marine isolates SJ(T), AQ and JS5(T) clustered in a separate clade from Bdellovibrio bacteriovorus 100(T) as part of the clade that contains Bacteriovorax spp., indicating a much closer taxonomic relationship to the latter. DNA-DNA hybridization experiments also demonstrated <5% similarity between Bdellovibrio bacteriovorus 100(T) and the marine isolates. Distinct differences between the salt-water group and Bdellovibrio spp. were also observed by determination of DNA G + C content, salinity growth testing and antibiotic sensitivity analysis. On the basis of the results from the studies described above, it is proposed that marine isolates SjT (=ATCC BAA-682(T) = DSM 15412(T)) and JS5(T) (=ATCC BAA-684(T) =DSM 15409(T)) should be classified within the genus Bacteriovorax as the type strains of Bacteriovorax marinus sp. nov. and Bacteriovorax litoralis sp. nov., respectively.