title: The Change of a Medically Important Genus: Worldwide Occurrence of Genetically Diverse Novel Brucella Species in Exotic Frogs.
abstract: The genus Brucella comprises various species of both veterinary and human medical importance. All species are genetically highly related to each other, sharing intra-species average nucleotide identities (ANI) of > 99%. Infections occur among various warm-blooded animal species, marine mammals, and humans. Until recently, amphibians had not been recognized as a host for Brucella. In this study, however, we show that novel Brucella species are distributed among exotic frogs worldwide. Comparative recA gene analysis of 36 frog isolates from various continents and different frog species revealed an unexpected high genetic diversity, not observed among classical Brucella species. In phylogenetic reconstructions the isolates consequently formed various clusters and grouped together with atypical more distantly related brucellae, like B. inopinata, strain BO2, and Australian isolates from rodents, some of which were isolated as human pathogens. Of one frog isolate (10RB9215) the genome sequence was determined. Comparative genome analysis of this isolate and the classical Brucella species revealed additional genetic material, absent from classical Brucella species but present in Ochrobactrum, the closest genetic neighbor of Brucella, and in other soil associated genera of the Alphaproteobacteria. The presence of gene clusters encoding for additional metabolic functions, flanked by tRNAs and mobile genetic elements, as well as by bacteriophages is suggestive for a different ecology compared to classical Brucella species. Furthermore it suggests that amphibian isolates may represent a link between free living soil saprophytes and the pathogenic Brucella with a preferred intracellular habitat. We therefore assume that brucellae from frogs have a reservoir in soil and, in contrast to classical brucellae, undergo extensive horizontal gene transfer.
authors.affiliation: Bundeswehr Institute of Microbiology, Neuherbergstrasse 11, Munich and German Center for Infection Research (DZIF), Munich, Germany.
authors.forename: Holger C
authors.initials: HC
authors.lastname: Scholz
authors.affiliation: Department of Wildlife Diseases, Leibniz Institute for Zoo and Wildlife Research, Germany.
authors.forename: Kristin
authors.initials: K
authors.lastname: Mühldorfer
authors.affiliation: Berrimah Veterinary Laboratories, Northern Territory Government, Berrimah, Northern Territory, Australia.
authors.forename: Cathy
authors.initials: C
authors.lastname: Shilton
authors.affiliation: Berrimah Veterinary Laboratories, Northern Territory Government, Berrimah, Northern Territory, Australia.
authors.forename: Suresh
authors.initials: S
authors.lastname: Benedict
authors.affiliation: Animal & Plant Health Agency, Woodham Lane, Addlestone, United Kingdom.
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Whatmore
authors.affiliation: Center for Biotechnology, CeBiTec, Universität Bielefeld, Bielefeld, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Blom
authors.affiliation: Hessian State Laboratory (LHL), Schubertstrasse 60, Giessen, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Eisenberg
mesh_terms: D000818:Animals; D001001:Anura / Q000382:microbiology*; D001315:Australia; D002002:Brucella / Q000235:genetics*; D002006:Brucellosis / Q000382:microbiology; D004269:DNA, Bacterial / Q000235:genetics; D022761:Gene Transfer, Horizontal / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics; D006801:Humans; D042041:Ochrobactrum / Q000235:genetics; D010802:Phylogeny; D012377:Rodentia / Q000382:microbiology; D017422:Sequence Analysis, DNA / Q000379:methods
chemical_list: D004269:DNA, Bacterial