title: The third replicon of members of the Burkholderia cepacia Complex, plasmid pC3, plays a role in stress tolerance.
abstract: The metabolically versatile Burkholderia cepacia complex (Bcc) occupies a variety of niches, including the plant rhizosphere and the cystic fibrosis lung (where it is often fatal to the patient). Bcc members have multipartite genomes, of which the third replicon, pC3 (previously chromosome 3), has been shown to be a nonessential megaplasmid which confers virulence and both antifungal and proteolytic activity on several strains. In this study, pC3 curing was extended to cover strains of 16 of the 17 members of the Bcc, and the phenotypes conferred by pC3 were determined. B. cenocepacia strains H111, MCO-3, and HI2424 were previously cured of pC3; however, this had not proved possible in the epidemic strain K56-2. Here, we investigated the mechanism of this unexpected stability and found that efficient toxin-antitoxin systems are responsible for maintaining pC3 of strain K56-2. Identification of these systems allowed neutralization of the toxins and the subsequent deletion of K56-2pC3. The cured strain was found to exhibit reduced antifungal activity and was attenuated in both the zebrafish and the Caenorhabditis elegans model of infection. We used a PCR screening method to examine the prevalence of pC3 within 110 Bcc isolates and found that this replicon was absent in only four cases, suggesting evolutionary fixation. It is shown that plasmid pC3 increases the resistance of B. cenocepacia H111 to various stresses (oxidative, osmotic, high-temperature, and chlorhexidine-induced stresses), explaining the prevalence of this replicon within the Bcc.
authors: Department of Microbiology, Institute of Plant Biology, University of Zürich, Zürich, Switzerland.
authors: Kirsty
authors: K
authors: Agnoli
authors: Carmen
authors: C
authors: Frauenknecht
authors: Roman
authors: R
authors: Freitag
authors: Stephan
authors: S
authors: Schwager
authors: Christian
authors: C
authors: Jenul
authors: Annette
authors: A
authors: Vergunst
authors: Aurelien
authors: A
authors: Carlier
authors: Leo
authors: L
authors: Eberl
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism; D042602:Burkholderia cepacia complex / Q000235:genetics* / Q000502:physiology*; D017173:Caenorhabditis elegans / Q000382:microbiology; D017353:Gene Deletion; D042822:Genomic Instability; D012093:Replicon; D013312:Stress, Physiological; D016019:Survival Analysis; D014774:Virulence; D015027:Zebrafish / Q000382:microbiology
chemical_list: D001427:Bacterial Toxins