Absence of Membrane Phosphatidylcholine Does Not Affect Virulence and Stress Tolerance Phenotypes in the Opportunistic Pathogen Pseudomonas aeruginosa

During growth in presence of choline, both laboratory and clinical Pseudomonas aeruginosa strains synthesize phosphatidylcholine (PC), and PC makes up ∼4% of the total membrane phospholipid content. In all the strains tested, PC synthesis occurred only when choline is provided exogenously. Mutants defective in synthesis of PC were generated in the strain backgrounds PAO1 and PA14. Minimum inhibitory concentration studies testing sensitivity of PC-deficient strains towards various antibiotics and cationic antimicrobial peptides revealed no differences as compared to wild-type strains. Mutants incapable of synthesizing PC were also found to be unaffected in motility and biofilm formation on abiotic surfaces, colonization of biotic surfaces and virulence in a mouse infection model. A global phenotypic microarray was further used to identify conditions wherein membrane PC may play a role of in P. aeruginosa. No culture conditions were identified wherein wild-type and PC-deficient mutants showed phenotypic differences. Membrane PC may serve a highly specific role during P. aeruginosa interactions with its eukaryotic hosts based on all the clinical strains tested retaining the ability to synthesize it during availability of choline.在添加胆碱的培养条件下，实验室菌株与临床分离的铜绿假单胞菌（Pseudomonas aeruginosa）均可合成磷脂酰胆碱（phosphatidylcholine，PC），且PC约占细胞膜总磷脂含量的4%。所有受试菌株均仅在外源提供胆碱时才可合成PC。研究人员在PAO1与PA14菌株的遗传背景中构建了PC合成缺陷突变株。通过最低抑菌浓度（minimum inhibitory concentration，MIC）实验检测PC缺陷株对多种抗生素与阳离子抗菌肽的敏感性，结果显示其与野生型菌株无显著差异。研究还发现，无法合成PC的突变株，其在非生物表面的运动能力、生物被膜形成能力、生物表面定殖能力，以及小鼠感染模型中的毒力均未受影响。研究人员进一步采用全局表型芯片技术，筛选铜绿假单胞菌中细胞膜PC可能发挥功能的培养条件，但未发现任何可使野生型菌株与PC缺陷突变株出现表型差异的培养环境。结合所有受试临床菌株在胆碱存在时均可合成PC的实验结果，推测细胞膜PC可能在铜绿假单胞菌与真核宿主的相互作用中发挥高度特异性的功能。