P. aeruginosa
not annotated - annotated - LINNAEUS only
21097632
Acyl-homoserine lactone binding to and stability of the orphan Pseudomonas aeruginosa quorum-sensing signal receptor QscR.
The Pseudomonas aeruginosa transcription factor QscR responds to a variety of fatty acyl-homoserine lactones (HSLs), including N-3-oxododecanoyl-HSL (3OC12-HSL), which is produced and detected by the P. aeruginosa quorum-sensing circuit LasI and LasR. As is true for LasR and many other acyl-HSL-dependent transcription factors, production of soluble QscR in sufficient amounts for purification requires growth of recombinant bacteria in the presence of an appropriate acyl-HSL. QscR is thought to bind 3OC12-HSL relatively weakly compared to LasR, and unlike LasR, binding of purified QscR to target DNA was shown to strongly depend on exogenously added 3OC12-HSL. We show that purified QscR is dimeric at sufficiently high concentrations and monomeric at lower concentrations. Furthermore, QscR bound 3OC12-HSL more tightly than previously believed. Purified QscR retained 3OC12-HSL, and at sufficiently high concentrations, it bound target DNA in the absence of added 3OC12-HSL. We also obtained soluble QscR from recombinant Escherichia coli grown in the presence of N-3-oxohexanoyl-HSL (3OC6-HSL) instead of 3OC12-HSL, and because 3OC6-HSL bound much more loosely to QscR than other acyl-HSLs tested, we were able to exchange 3OC6-HSL with other acyl-HSLs in vitro and then estimate binding affinities of QscR for different acyl-HSLs and for target DNA. Our data support a model whereby QscR polypeptides fold properly in the absence of an acyl-HSL, but soluble, acyl-HSL-free QscR does not accumulate because it is subject to rapid aggregation or proteolysis.
21169488
The sensor kinase CbrA is a global regulator that modulates metabolism, virulence, and antibiotic resistance in Pseudomonas aeruginosa.
Pseudomonas aeruginosa is an opportunistic pathogen that possesses a large arsenal of virulence factors enabling the pathogen to cause serious infections in immunocompromised patients, burn victims, and cystic fibrosis patients. CbrA is a sensor kinase that has previously been implied to play a role with its cognate response regulator CbrB in the metabolic regulation of carbon and nitrogen utilization in P. aeruginosa. Here it is demonstrated that CbrA and CbrB play an important role in various virulence and virulence-related processes of the bacteria, including swarming, biofilm formation, cytotoxicity, and antibiotic resistance. The cbrA deletion mutant was completely unable to swarm while exhibiting an increase in biofilm formation, supporting the inverse regulation of swarming and biofilm formation in P. aeruginosa. The cbrA mutant also exhibited increased cytotoxicity to human lung epithelial cells as early as 4 and 6 h postinfection. Furthermore, the cbrA mutant demonstrated increased resistance toward a variety of clinically important antibiotics, including polymyxin B, ciprofloxacin, and tobramycin. Microarray analysis revealed that under swarming conditions, CbrA regulated the expression of many genes, including phoPQ, pmrAB, arnBCADTEF, dnaK, and pvdQ, consistent with the antibiotic resistance and swarming impairment phenotypes of the cbrA mutant. Phenotypic and real-time quantitative PCR (RT-qPCR) analyses of a PA14 cbrB mutant suggested that CbrA may be modulating swarming, biofilm formation, and cytotoxicity via CbrB and that the CrcZ small RNA is likely downstream of this two-component regulator. However, as CbrB did not have a resistance phenotype, CbrA likely modulates antibiotic resistance in a manner independent of CbrB.
21148734
Relating the physical properties of Pseudomonas aeruginosa lipopolysaccharides to virulence by atomic force microscopy.
Lipopolysaccharides (LPS) are an important class of macromolecules that are components of the outer membrane of Gram-negative bacteria such as Pseudomonas aeruginosa. P. aeruginosa contains two different sugar chains, the homopolymer common antigen (A band) and the heteropolymer O antigen (B band), which impart serospecificity. The characteristics of LPS are generally assessed after isolation rather than in the context of whole bacteria. Here we used atomic force microscopy (AFM) to probe the physical properties of the LPS of P. aeruginosa strain PA103 (serogroup O11) in situ. This strain contains a mixture of long and very long polymers of O antigen, regulated by two different genes. For this analysis, we studied the wild-type strain and four mutants, DeltaWzz1 (producing only very long LPS), DeltaWzz2 (producing only long LPS), DDeltaM (with both the wzz1 and wzz2 genes deleted), and Wzy::GM (producing an LPS core oligosaccharide plus one unit of O antigen). Forces of adhesion between the LPS on these strains and the silicon nitride AFM tip were measured, and the Alexander and de Gennes model of steric repulsion between a flat surface and a polymer brush was used to calculate the LPS layer thickness (which we refer to as length), compressibility, and spacing between the individual molecules. LPS chains were longest for the wild-type strain and DeltaWzz1, at 170.6 and 212.4 nm, respectively, and these values were not statistically significantly different from one another. Wzy::GM and DDeltaM have reduced LPS lengths, at 34.6 and 37.7 nm, respectively. Adhesion forces were not correlated with LPS length, but a relationship between adhesion force and bacterial pathogenicity was found in a mouse acute pneumonia model of infection. The adhesion forces with the AFM probe were lower for strains with LPS mutations, suggesting that the wild-type strain is optimized for maximal adhesion. Our research contributes to further understanding of the role of LPS in the adhesion and virulence of P. aeruginosa.