The genome sequence of Brucella pinnipedialis B2/94 sheds light on the evolutionary history of the genus Brucella

Stéphane Audic,Magali Lescot,Jean-Michel Claverie,Axel Cloeckaert,Michel S Zygmunt

doi:10.1186/1471-2148-11-200

Abstract

BackgroundSince the discovery of the Malta fever agent, Brucella melitensis, in the 19th century, six terrestrial mammal-associated Brucella species were recognized over the next century. More recently the number of novel Brucella species has increased and among them, isolation of species B. pinnipedialis and B. ceti from marine mammals raised many questions about their origin as well as on the evolutionary history of the whole genus.ResultsWe report here on the first complete genome sequence of a Brucella strain isolated from marine mammals, Brucella pinnipedialis strain B2/94. A whole gene-based phylogenetic analysis shows that five main groups of host-associated Brucella species rapidly diverged from a likely free-living ancestor close to the recently isolated B. microti. However, this tree lacks the resolution required to resolve the order of divergence of those groups. Comparative analyses focusing on a) genome segments unshared between B. microti and B. pinnipedialis, b) gene deletion/fusion events and c) positions and numbers of Brucella specific IS711 elements in the available Brucella genomes provided enough information to propose a branching order for those five groups.ConclusionsIn this study, it appears that the closest relatives of marine mammal Brucella sp. are B. ovis and Brucella sp. NVSL 07-0026 isolated from a baboon, followed by B. melitensis and B. abortus strains, and finally the group consisting of B. suis strains, including B. canis and the group consisting of the single B. neotomae species. We were not able, however, to resolve the order of divergence of the two latter groups.

Highlights

Since the discovery of the Malta fever agent, Brucella melitensis, in the 19th century, six terrestrial mammal-associated Brucella species were recognized over the century
The 23S rDNA sequence of B. pinnipedialis B2/94 was found similar to that of other Brucella species, in contrast with the anomalous and unexpected 23S ribosomal RNA sequence previously described for B. microti [30]
Genome structure and whole gene set phylogeny The phylogenetic placement of B. pinnipedialis B2/94 was assessed with the help of a whole gene tree including all orthologous genes from Brucella strains available in the complete genome division of GenBank, completed by sequence data from selected Brucella strains of particular phylogenetic relevance, either deposited in the whole genome shotgun (WGS) division of GenBank, or available from other sources

Summary

Introduction

Since the discovery of the Malta fever agent, Brucella melitensis, in the 19th century, six terrestrial mammal-associated Brucella species were recognized over the century. Six species were initially recognized within the genus Brucella: B. abortus, B. melitensis, B. suis, B. ovis, B. canis, and B. neotomae [1,2,3] This classification is mainly based on differences in pathogenicity, host preference, and phenotypic characteristics. Molecular and phenotypic typing of marine mammal Brucella strains led to their classification into two species, B. ceti and B. pinnipedialis, according to their preferred host, cetaceans and pinnipeds respectively [5]. Three human cases with naturally acquired infection by Brucella strains presumably from marine origin were reported, one case of spinal osteomyelitis from a patient in New Zealand [20] and two neurobrucellosis cases from Peruvian patients [21] These human isolates exhibited the same genotype as strains from cetaceans from the Pacific [22]

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Conclusion