for its ability to cause chronic infections and for persisting on implanted medical devices. The PC-deficient Ligustilide site strains were assayed for biofilm formation on plastic using 96-well microtiter plates. While the pel mutant, which is defective in synthesis of extracellular matrix, and the flagellum-deficient flgK mutant formed biofilms that were significantly smaller than WT as previously published, PC-deficient mutants were not altered in their ability to form biofilms. These data show that PC formation does not impact P. aeruginosa motility or biofilm formation on abiotic surfaces. PC is not required for colonization of biotic surfaces or virulence To assess the role of PC in host cell-pathogen interactions, PCdeficient P. aeruginosa strains were tested for colonization of eukaryotic host surfaces using two model systems: the human airway epithelial cell co-culture model and the fungal co culture model. PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/22179956 In the airway epithelial cell model, P. aeruginosa PAO1 colonization was assessed after co-culture for 1 hour for enumerating initial attachment and after 6 hours for enumerating biofilm formation. At each of these time points, microscopic examination revealed that the integrity of epithelial cell monolayers had not been compromised following addition of P. aeruginosa. Fig. 3A shows that after 1 h post inoculation, about 25% of the cells present in the initial inocula of P. aeruginosa PAO1 WT and PAO1 Dpcs had attached to the epithelial cells. In contrast, the PAO1 flgk::Tn7 mutant showed a 15-fold lower initial attachment, as has been described previously. At 5 hours post initial attachment, a 10-fold increase in both P. aeruginosa PAO1 WT and PAO1Dpcs CFUs was observed due to growth of the strains, whereas the PAO1 flgk::Tn7 showed 5.5 fold lower CFUs compared to the PAO1 WT and PAO1Dpcs strains. In the fungal co-culture model, PA14 strains and the constitutively-filamentous Candida albicans nrg1/nrg1 strains were cultured for 48 hours. Under these conditions P. aeruginosa PA14 WT attach, form biofilms on the fungal surface, and eventually kill the fungus. As shown in Fig. 3C, the addition of choline to the culture medium enhanced PA14 WT biofilm formation. However, comparison of PA14 WT and PA14Dpcs biofilms on the fungal surface in medium with choline revealed no distinguishable differences. Several studies have shown hemolytic phospholipase C and T3SS to play key roles in P. aeruginosa virulence towards its eukaryotic hosts. Using in vitro assays, we tested whether changes in P. aeruginosa membranes due to PC synthesis affects the production of these virulence factors. PlcH activity was analyzed using the artificial substrate pnitrophenyl-phosphorylcholine . Cultures of PA14 WT, Dpcs and DplcHR were grown in defined medium with or without choline and the supernatants were analyzed for NPPC activity. In WT supernatants, presence of choline in the medium resulted in 6-fold higher phospholipase C activity while no increase 
in activity was observed in the DplcHR strain, a mutant defective in synthesis of phospholipase C. In comparison, no difference in induction of NPPC activity was observed in Dpcs mutant as compared to WT . While P. aeruginosa PAO1 strains can form biofilms on airway epithelial cells in a co-culture model as described above, P. aeruginosa Membrane Phosphatidylcholine structural component of the T3SS translocase, showed 4-fold lower percent cytotoxicity as compared to PA14 WT. In comparison, PA14 Dpcs was not defective in
