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Phylogenetic relationships amongst the saltwater members of the genus Bacteriovorax using rpoB sequences and reclassification of Bacteriovorax stolpii as Bacteriolyticum stolpii gen. nov., comb. nov.

¹ Department of Medical and Research Technology, School of Medicine, University of Maryland, Allied Health Building, 100 Penn Street, Baltimore, MD 21201, USA
² Environmental Sciences Institute, Florida A&M University, 1515 M. L. King, Jr Blvd., Tallahassee, FL 32307, USA
³ Department of Epidemiology and Preventative Medicine, School of Medicine, University of Maryland, 10 South Pine Street, Baltimore, MD 21201, USA

Correspondence
Silvia A. Piñeiro
spineiro{at}som.umaryland.edu

Members of the saltwater genus Bacteriovorax, formerly known as the marine Bdellovibrio, are obligate predatory bacteria that prey selectively on other Gram-negative bacteria. Previous phylogenetic analysis based on the 16S rRNA genes of saltwater Bacteriovorax isolates from environmental samples revealed 11 distinct phylogenetic clusters based on 96.5 % gene sequence similarity. In other micro-organisms, the gene coding for the β-subunit of RNA polymerase (rpoB) has been shown to be more discriminating than 16S rRNA genes. In this study, rpoB sequences from Bacteriovorax isolates were analysed to determine whether the results would be consistent with those based on 16S rRNA gene sequences. A 1242 bp region of the rpoB gene from 74 saltwater Bacteriovorax strains and two freshwater isolates, Bacteriovorax stolpii Uki2^T and Peredibacter starrii A3.12^T, was amplified by PCR and analysed. The sequences were aligned and phylogenetic trees were constructed using a neighbour-joining algorithm. The resulting tree showed that the rpoB sequences produced smaller subdivisions of isolates, but were nevertheless consistent with the clusters determined using 16S rRNA gene sequences. Thus, the highly conserved 16S rRNA gene sequences provided good phylogenetic information and the rpoB gene sequences permitted greater differentiation in order to further subdivide phylogenetically distinct groups within the genus Bacteriovorax. Also, on the basis of the extensive diversity and large distance between the saltwater members of the genus Bacteriovorax and the freshwater/soil Bacteriovorax, a reclassification of Bacteriovorax stolpii as Bacteriolyticum stolpii gen. nov., comb. nov. is proposed. A new family, Peredibacteraceae fam. nov., is also described.

The GenBank/EMBL/DDBJ accession numbers for the rpoB gene sequences determined in this study are EF536750–EF536823 and EU240892–EU240893.