Intraspecies signaling involving the diffusible signal factor BDSF (cis-2-dodecenoic acid) influences virulence in Burkholderia cenocepacia

Abstract

Burkholderia cenocepacia produces a diffusible fatty acid signal molecule, cis-2-dodecenoic acid (BDSF), that has been implicated in interspecies and interkingdom communication. Here, we show that BDSF also acts as an intraspecies signal in B. cenocepacia to control factors contributing to virulence of this major opportunistic pathogen.

FIG. 1.

Effect of mutation of rpfF on the expression of selected genes in B. cenocepacia J2315. (A) Effect of rpfF mutation on the expression of genes encoding proteins with altered abundance as determined by proteomic analysis. (B) Effect of mutation of rpfF on expression of cbl genes. (C) Addition of 50 μM exogenous BDSF or complementation of rpfF mutation using pBcam0581 restores the transcript levels for cblD, cblS, and cblA to wild-type levels. Transcript levels of all genes were measured by RT-PCR. Bacterial strains were grown to an optical density at 600 nm of 0.8 in M9 medium before RNA extraction. Data were normalized to 16S RNA, and each is presented as n-fold change with respect to the wild-type B. cenocepacia J2315 for each gene. Negative values indicate n-fold reductions. Data (means ± the standard deviation) are representative of the results for three independent biological experiments.

FIG. 2.

Loss of BDSF signaling through mutation of rpfF has multiple phenotypic effects in B. cenocepacia J2315. The rpfF mutant showed reduced motility in 0.6% Eiken agar (A), reduced adherence to porcine mucin (B), and reduced biofilm formation (C), as quantified by crystal violet staining. These phenotypes were restored to wild-type levels by complementation with pBcam0581. Each experiment was performed at least three times in triplicate. Error bars represent the standard errors of the mean.

FIG. 3.

Virulence of Burkholderia cenocepacia strains in the Galleria mellonella larva infection model. Larvae were injected with 10⁶ bacteria and monitored for survival 24 h postinfection. Each bar is representative of the results for five independent trials (n = 10), and standard deviations are shown.