The AHL- and BDSF-Dependent Quorum Sensing Systems Control Specific and Overlapping Sets of Genes in Burkholderia cenocepacia H111

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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.

Section: Methodsmentioning

confidence: 99%

The Third Replicon of Members of the Burkholderia cepacia Complex, Plasmid pC3, Plays a Role in Stress Tolerance

Agnoli

Frauenknecht

Freitag

et al. 2014

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“…In contrast, when we used a more permissive P value threshold, a potential 54 binding site was found upstream of bapA (P ϭ 0.0016) (TGGTTGAACGTTTGCC), suggesting a potential direct regulation and adding an extra layer of complexity to the regulation of this gene, which has been shown to be regulated by two quorum sensing molecules, N-octanoyl homoserine lactone (C 8 -HSL) and BDSF (Burkholderia diffusible signal factor; cis-2-dodecenoic acid) (62).…”

Section: Fig 2 Box Plot For the Numbers Of Reads Per Kilobase Per Milmentioning

confidence: 99%

σ ⁵⁴ -Dependent Response to Nitrogen Limitation and Virulence in Burkholderia cenocepacia Strain H111

Lardi

Aguilar

Pedrioli

et al. 2015

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Members of the genus Burkholderia are versatile bacteria capable of colonizing highly diverse environmental niches. In this study, we investigated the global response of the opportunistic pathogen Burkholderia cenocepacia H111 to nitrogen limitation at the transcript and protein expression levels. In addition to a classical response to nitrogen starvation, including the activation of glutamine synthetase, PII proteins, and the two-component regulatory system NtrBC, B. cenocepacia H111 also upregulated polyhydroxybutyrate (PHB) accumulation and exopolysaccharide (EPS) production in response to nitrogen shortage. A search for consensus sequences in promoter regions of nitrogen-responsive genes identified a 54 consensus sequence. The mapping of the 54 regulon as well as the characterization of a 54 mutant suggests an important role of 54 not only in control of nitrogen metabolism but also in the virulence of this organism.

“…These studies analyzed the QS-dependent expression profiles in Burkholderia cenocepacia (27), B. thailandensis (28), Burkholderia gladioli (29), and B. mallei and B. pseudomallei (30). While B. thailandensis is a nonpathogenic tropical soil microorganism, B. cenocepacia, B. mallei, and B. pseudomallei are considered human and animal pathogens (31)(32)(33).…”

mentioning

confidence: 99%

Genome-Wide RNA Sequencing Analysis of Quorum Sensing-Controlled Regulons in the Plant-Associated Burkholderia glumae PG1 Strain

Gao

Krysciak

Petersen

et al. 2015

dBurkholderia glumae PG1 is a soil-associated motile plant-pathogenic bacterium possessing a cell density-dependent regulation system called quorum sensing (QS). Its genome contains three genes, here designated bgaI1 to bgaI3, encoding distinct autoinducer-1 (AI-1) synthases, which are capable of synthesizing QS signaling molecules. Here, we report on the construction of B. glumae PG1 ⌬bgaI1, ⌬bgaI2, and ⌬bgaI3 mutants, their phenotypic characterization, and genome-wide transcriptome analysis using RNA sequencing (RNA-seq) technology. Knockout of each of these bgaI genes resulted in strongly decreased motility, reduced extracellular lipase activity, a reduced ability to cause plant tissue maceration, and decreased pathogenicity. RNA-seq analysis of all three B. glumae PG1 AI-1 synthase mutants performed in the transition from exponential to stationary growth phase revealed differential expression of a significant number of predicted genes. In comparison with the levels of gene expression by wild-type strain B. glumae PG1, 481 genes were differentially expressed in the ⌬bgaI1 mutant, 213 were differentially expressed in the ⌬bgaI2 mutant, and 367 were differentially expressed in the ⌬bgaI3 mutant. Interestingly, only a minor set of 78 genes was coregulated in all three mutants. The majority of the QS-regulated genes were linked to metabolic activities, and the most pronounced regulation was observed for genes involved in rhamnolipid and Flp pilus biosynthesis and the type VI secretion system and genes linked to a clustered regularly interspaced short palindromic repeat (CRISPR)-cas gene cluster. Q uorum sensing (QS) is a cell density-dependent gene regulation system in bacteria (1) in which the population density is sensed through the accumulation of bacterially produced signaling molecules called autoinducers (AIs). This cell-to-cell signaling process allows the microbial population to synchronize group behavior and alter its gene expression accordingly. QS is involved in a wide array of regulatory circuits, among which are pathogenicity, secretion of extracellular proteins, secondary metabolite production, and others (2). Key QS signaling molecules in many Gram-negative bacteria are N-acyl-homoserine lactones (AHLs) (3-5), synthesized mainly through LuxI homologs (EC 2.3.1.184) using S-adenosylmethionine (SAM), and an acyl-acyl carrier protein (acyl-ACP) from the fatty acid biosynthesis pathway (6). LuxR-type receptor/regulator proteins are involved in AHL signal perception. Together with LuxR, other proteins may be part of this regulatory circuit.The motile, rod-shaped Gram-negative soil bacterium Burkholderia glumae is considered to be a seed-borne pathogen that causes panicle blight of rice (7). B. glumae has also been reported to infect other plant species, like tomato, sunflower, and pepper (8, 9). Although it is not classified as a human pathogen, a single case of the isolation of B. glumae from a clinical sample was reported (10), indicating that at least some strains of this pathogen may be associated w...