Diversity and evolution of Bdellovibrio-and-like organisms (BALOs), reclassification of Bacteriovorax starrii as Peredibacter starrii gen. nov., comb. nov., and description of the Bacteriovorax-Peredibacter clade as Bacteriovoracaceae fam. nov.

A phylogenetic analysis of Bdellovibrio-and-like organisms (BALOs) was performed. It was based on the characterization of 71 strains and on all consequent 16S rRNA gene sequences available in databases, including clones identified by data-mining, totalling 120 strains from very varied biotopes. Amplified rDNA restriction analysis (ARDRA) accurately reflected the diversity and phylogenetic affiliation of BALOs, thereby providing an efficient screening tool. Extensive phylogenetic analysis of the 16S rRNA gene sequences revealed great diversity within the Bdellovibrio ( > 14% divergence) and Bacteriovorax ( > 16%) clades, which comprised nine and eight clusters, respectively, exhibiting more than 3% intra-cluster divergence. The clades diverged by more than 20%. The analysis of conserved 16S rRNA secondary structures showed that Bdellovibrio contained motifs atypical of the delta-Proteobacteria, suggesting that it is ancestral to Bacteriovorax. While none of the Bdellovibrio strains were of marine origin, Bacteriovorax included separate soil/freshwater and marine-specific groups. On the basis of their extensive diversity and the large distance separating the groups, it is proposed that Bacteriovorax starrii be placed into a new genus, Peredibacter gen. nov., with Peredibacter starrii A3.12(T) ( = ATCC 15145(T) = NCCB 72004(T)) as its type strain. Also proposed is a redefinition of the Bdellovibrio and the Bacteriovorax-Peredibacter lineages as two different families, i.e. 'Bdellovibrionaceae' and a new family, Bacteriovoracaceae. Also, a re-evaluation of oligonucleotides targeting BALOs is presented, and the implications of the large diversity of these organisms and of their distribution in very different environments are discussed.