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Structure of Pseudomonas aeruginosa Populations Analyzed by Single Nucleotide Polymorphism and Pulsed-Field Gel Electrophoresis Genotyping. Gracia Morales, 2004.Pseudomonas aeruginosa has a wide ecological distribution that includes natural habitats and clinical settings . To analyze the population structure and distribution of P . aeruginosa, a collection of 111 isolates of diverse habitats and geographical origin, most of which contained a genome with a different SpeI macrorestriction profile, was typed by restriction fragment length polymorphism based on 14 single nucleotide polymorphisms (SNPs) located at seven conserved loci of the core genome (oriC, oprL, fliC, alkB2, citS, oprI, and ampC) . The combination of these SNPs plus the type of fliC present (a or b) allowed the assignment of a genetic fingerprint to each strain, thus providing a simple tool for the discrimination of P . aeruginosa strains . Thirteen of the 91 identified SNP genotypes were found in two or more strains . In several cases, strains sharing their SNP genotype had different SpeI macrorestriction profiles . The highly virulent CHA strain shared its SNP genotype with other strains that had different SpeI genotypes and which had been isolated from nonclinical habitats . The reference strain PAO1 also shared its SNP genotype with other strains that had different SpeI genotypes . The P . aeruginosa chromosome contains a conserved core genome and variable amounts of accessory DNA segments (genomic islands and islets) that can be horizontally transferred among strains . The fact that some SNP genotypes were overrepresented in the P . aeruginosa population studied and that several strains sharing an SNP genotype had different SpeI macrorestriction profiles supports the idea that changes occur at a higher rate in the accessory DNA segments than in the conserved core genome . Utilization of Acyl-Homoserine Lactone Quorum Signals for Growth by a Soil Pseudomonad and Pseudomonas aeruginosa PAO1. Jean J. Huang, 2003.Acyl-homoserine lactones (AHLs) are employed by several Proteobacteria as quorum-sensing signals . Past studies have established that these compounds are subject to biochemical decay and can be used as growth nutrients . Here we describe the isolation of a soil bacterium, Pseudomonas strain PAI-A, that degrades 3-oxododecanoyl-homoserine lactone (3OC12HSL) and other long-acyl, but not short-acyl, AHLs as sole energy sources for growth . The small-subunit rRNA gene from strain PAI-A was 98.4% identical to that of Pseudomonas aeruginosa, but the soil isolate did not produce obvious pigments or AHLs or grow under denitrifying conditions or at 42°C . The quorum-sensing bacterium P . aeruginosa, which produces both 3OC12HSL and C4HSL, was examined for the ability to utilize AHLs for growth . It did so with a specificity similar to that of strain PAI-A, i.e., degrading long-acyl but not short-acyl AHLs . In contrast to the growth observed with strain PAI-A, P . aeruginosa strain PAO1 growth on AHLs commenced only after extremely long lag phases . Liquid-chromatography-atmospheric pressure chemical ionization-mass spectrometry analyses indicate that strain PAO1 degrades long-acyl AHLs via an AHL acylase and a homoserine-generating HSL lactonase . A P . aeruginosa gene, pvdQ (PA2385), has previously been identified as being a homologue of the AHL acylase described as occurring in a Ralstonia species . Escherichia coli expressing pvdQ catalyzed the rapid inactivation of long-acyl AHLs and the release of HSL . P . aeruginosa engineered to constitutively express pvdQ did not accumulate its 3OC12HSL quorum signal when grown in rich media . However, pvdQ knockout mutants of P . aeruginosa were still able to grow by utilizing 3OC12HSL . To our knowledge, this is the first report of the degradation of AHLs by pseudomonads or other  -Proteobacteria, of AHL acylase activity in a quorum-sensing bacterium, of HSL lactonase activity in any bacterium, and of AHL degradation with specificity only towards AHLs with long side chains .
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