Bdellovibrio exovorus sp. nov., a novel predator of Caulobacter crescentus

The life cycle, prey range and taxonomic status of a Bdellovibrio-like organism, strain JSS^T, were studied. Strain JSS^T was isolated from sewage in London, Ontario, Canada, in enrichment culture with Caulobacter crescentus prey cells. During predation, this strain remained attached to the outside of a stalked C. crescentus cell. No periplasmic growth stage was observed and no bdelloplast was formed. The stalked cells of C. crescentus retained their shape and, after predation, were devoid of cytoplasmic content, as shown by transmission electron microscopy. A periplasmic growth stage has been a definitive character in the description of members of the genera Bdellovibrio, Bacteriovorax, Bacteriolyticum and Peredibacter. This is the first description of an epibiotic predator in this group of prokaryotic predators. The G+C content of the genomic DNA of strain JSS^T was 46.1 mol%. 16S rRNA gene sequence analysis showed that this strain was related to Bdellovibrio bacteriovorus strains HD100^T, 109J, 114 and 127 (90-93% similarity). Phylogenetic analysis based on 16S rRNA gene sequences grouped strain JSS^T with the Bdellovibrio cluster, but at a distance from other Bdellovibrio isolates. On the basis of features of the life cycle and phylogenetic data, it was concluded that strain JSS^T merits classification as the type strain of a novel species, for which the name Bdellovibrio exovorus sp. nov. is proposed (type strain JSS^T 5ATCC BAA-2330^T 5DSM 25223^T).