title: Exposing the third chromosome of Burkholderia cepacia complex strains as a virulence plasmid.
abstract: The Burkholderia cepacia complex (Bcc) consists of 17 closely related species of opportunistic bacterial pathogens, which are particularly problematic for cystic fibrosis patients and immunocompromised individuals. Bcc genomes consist of multiple replicons, and each strain sequenced to date has three chromosomes. In addition to genes thought to be essential for survival, each chromosome carries at least one rRNA operon. We isolated three mutants during a transposon mutagenesis screen that were non-pathogenic in a Caenorhabditis elegans infection model. It was demonstrated that these mutants had lost chromosome 3 (c3), and that the observed attenuation of virulence was a consequence of this. We constructed a c3 mini-replicon and used it to cure c3 from strains of several Bcc species by plasmid incompatibility, resulting in nine c3-null strains covering seven Bcc species. Phenotypic characterization of c3-null mutants revealed that they were attenuated in virulence in multiple infection hosts (rat, zebrafish, C. elegans, Galleria mellonella and Drosophila melanogaster), that they exhibited greatly diminished antifungal activity, and that c3 was required for d-xylose, fatty acid and pyrimidine utilization, as well as for exopolysaccharide production and proteolytic activity in some strains. In conclusion, we show that c3 is not an essential chromosomal element, rather a large plasmid that encodes virulence, secondary metabolism and other accessory functions in Bcc bacteria.
authors.affiliation: Department of Microbiology, Institute of Plant Biology, University of Zürich, Zollikerstrasse 107. CH-8008 Zürich, Switzerland.
authors.forename: K
authors.initials: K
authors.lastname: Agnoli
authors.forename: S
authors.initials: S
authors.lastname: Schwager
authors.forename: S
authors.initials: S
authors.lastname: Uehlinger
authors.forename: A
authors.initials: A
authors.lastname: Vergunst
authors.forename: D F
authors.initials: DF
authors.lastname: Viteri
authors.forename: D T
authors.initials: DT
authors.lastname: Nguyen
authors.forename: P A
authors.initials: PA
authors.lastname: Sokol
authors.forename: A
authors.initials: A
authors.lastname: Carlier
authors.forename: L
authors.initials: L
authors.lastname: Eberl
mesh_terms: D000818:Animals; D019121:Burkholderia Infections / Q000382:microbiology / Q000401:mortality / Q000473:pathology; D042602:Burkholderia cepacia complex / Q000235:genetics* / Q000472:pathogenicity*; D017173:Caenorhabditis elegans; D002876:Chromosomes, Bacterial; D004251:DNA Transposable Elements; D004195:Disease Models, Animal; D004331:Drosophila melanogaster; D007915:Lepidoptera; D053858:Metabolic Networks and Pathways / Q000235:genetics; D016254:Mutagenesis, Insertional; D009154:Mutation; D010957:Plasmids; D051381:Rats; D017384:Sequence Deletion; D016019:Survival Analysis; D037521:Virulence Factors / Q000235:genetics*; D015027:Zebrafish
chemical_list: D004251:DNA Transposable Elements; D037521:Virulence Factors