title: A simple alfalfa seedling infection model for Pseudomonas aeruginosa strains associated with cystic fibrosis shows AlgT (sigma-22) and RhlR contribute to pathogenesis.
abstract: A sensitive plant infection model was developed to identify virulence factors in nontypeable, alginate overproducing (mucoid) Pseudomonas aeruginosa strains isolated from cystic fibrosis (CF) patients with chronic pulmonary disease. Nontypeable strains with defects in lipopolysaccharide O-side chains are common to CF and often exhibit low virulence in animal models of infection. However, 1,000 such bacteria were enough to show disease symptoms in the alfalfa infection. A typical mucoid CF isolate, FRD1, and its isogenic mutants were tested for alfalfa seedling infection. Although defects in the global regulators Vfr, RpoS, PvdS, or LasR had no discernable effect on virulence, a defect in RhlR reduced the infection frequency by >50%. A defect in alginate biosynthesis resulted in plant disease with >3-fold more bacteria per plant, suggesting that alginate overproduction attenuated bacterial growth in planta. FRD1 derivatives lacking AlgT, a sigma factor required for alginate production, were reduced >50% in the frequency of infection. Thus, AlgT apparently regulates factors in FRD1, besides alginate, important for pathogenesis. In contrast, in a non-CF strain, PAO1, an algT mutation did not affect its virulence on alfalfa. Conversely, PAO1 virulence was reduced in a mucA mutant that overproduced alginate. These observations suggested that mucoid conversion in CF may be driven by a selection for organisms with attenuated virulence or growth in the lung, which promotes a chronic infection. These studies also demonstrated that the wounded alfalfa seedling infection model is a useful tool to identify factors contributing to the persistence of P. aeruginosa in CF.
authors.affiliation: Department of Microbiology and Immunology, Medical College of Virginia Campus of Virginia Commonwealth University, Richmond 23298-0678, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Silo-Suh
authors.forename: Sang-Jin
authors.initials: SJ
authors.lastname: Suh
authors.forename: Pamela A
authors.initials: PA
authors.lastname: Sokol
authors.forename: Dennis E
authors.initials: DE
authors.lastname: Ohman
mesh_terms: D000464:Alginates / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D003550:Cystic Fibrosis / Q000382:microbiology*; D006025:Glycosaminoglycans / Q000096:biosynthesis / Q000502:physiology*; D006801:Humans; D008297:Male; D000455:Medicago sativa / Q000382:microbiology*; D008863:Microspheres; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology*; D018410:Pneumonia, Bacterial / Q000382:microbiology; D011552:Pseudomonas Infections / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D051381:Rats; D017207:Rats, Sprague-Dawley; D036226:Seedlings / Q000382:microbiology; D012808:Sigma Factor / Q000235:genetics / Q000502:physiology*; D014774:Virulence / Q000235:genetics
chemical_list: C079619:AlgU protein, Pseudomonas aeruginosa; D000464:Alginates; D001426:Bacterial Proteins; D006025:Glycosaminoglycans; C107895:MucA protein, Pseudomonas; C086515:RhlR protein, Pseudomonas aeruginosa; D012808:Sigma Factor; C046129:mucoid exopolysaccharide (P aeruginosa)