Sobral, B. and A. Wattam (2011). Comparative genomics and phylogenomics of the Brucella. Book chapter in “Brucella: Molecular Microbiology and Genetics”. I. L.-G. D. O’Callaghan, Horizon Scientific Press.
Brucella species are characterized by extremely high levels of nucleotide similarity and yet vary in microbial and disease phenotypes, as well as in pathogenicity and host preference. These variations initially resulted in classification of six species; B. abortus, B. canis, B. melitensis, B. neotomae, B. ovis and B. suis. The lack of sequence diversity has inhibited molecular studies, but the development of new techniques and the recent availability of genome sequences have revealed interesting differences, including the expansion of the known Brucella species.
Recently, the Brucella genus has expanded by the discovery of four new species, B. ceti and B. pinnipedialis from marine mammals, B. inopinata from new human isolates, and B. microti, isolated from a rodent in the Czech Republic . An as yet unnamed isolate from Australian rodents might also be classified as a new species. This review summarizes the current state of knowledge of the genetic diversity within Brucella, including both the classical and new species, with particular emphasis on comparing the genome sequences, the phylogenies produced by a variety of methods and specific families of genes in particular functions and pathways.