Brucellae are facultative intracellular pathogens that belong to α-proteobacteria and may cause severe infections (brucellosis) in humans and animals. The genus currently consists of eleven species that can be divided in (I) the classical species (B. melitensis, B. abortus, B. suis, B. canis, B. ovis, & B. neotomae), (II) marine brucellae (B. ceti and B. pinnipedialis) and (III) the atypical species B. microti, B. papionis, and B. inopinata. All Brucella species are genetically highly related with overall genome similarities of >90% at the nucleotide level. Up to now, only little is known about mobile genetic elements of these pathogens. Neither plasmids nor temperate phages have been described in brucellae.
In this work, we analysed genomic sequences of various reference and type strains of the GenBank database (National Center for Biotechnology Information) and identified a number of putative prophages residing within the Brucella chromosomes. By mitomycin C induction, a phage of the family Siphoviridae was isolated from B. inopinata strain BO1. Phage BiPBO1 infects several Brucella species including B. abortus and B. melitensis. Integration of the phage genome occurs adjacent to a tRNA gene in chromosome 1. The bacterial and phage attachment sites comprise an identical sequence of 46 bp. This sequence exists in many Brucella and Ochrobactrum species. The BiPBO1 genome is composed of a 46,877 bp double-stranded DNA. Eighty-seven putative gene products were determined, of which 32 could be functionally assigned. Strongest similarities were found to a temperate phage residing in the chromosome of O. anthropi ATCC 49188 and to prophages identified in several families belonging to the order rhizobiales. Our data underline the close relationship between pathogenic Brucella and environmental Ochrobactrum species.