Périnet Simone, Jeukens Julie, Kukavica-Ibrulj Irena, Ouellet Myriam M, Charette Steve J, Levesque Roger C
Institut de Biologie Intégrative et des Systèmes, Université Laval, Québec, QC, Canada.
Département de microbiologie-infectiologie-immunologie, Faculté de Médecine, Université Laval, Québec, QC, Canada.
BMC Res Notes. 2016 Jan 12;9:23. doi: 10.1186/s13104-016-1840-x.
Mechanisms underlying the success of Pseudomonas aeruginosa in chronic lung infection among cystic fibrosis (CF) patients are poorly defined. The modA gene was previously linked to in vivo competitiveness of P. aeruginosa by a genetic screening in the rat lung. This gene encodes a subunit of transporter ModABC, which is responsible for extracellular uptake of molybdate. This compound is essential for molybdoenzymes, including nitrate reductases. Since anaerobic growth conditions are known to occur during CF chronic lung infection, inactivation of a molybdate transporter could inhibit proliferation through the inactivation of denitrification enzymes. Hence, we performed phenotypic characterization of a modA mutant strain obtained by signature-tagged mutagenesis (STM_modA) and assessed its virulence in vivo with two host models.
The STM_modA mutant was in fact defective for anaerobic growth and unable to use nitrates in the growth medium for anaerobic respiration. Bacterial growth and nitrate usage were restored when the medium was supplemented with molybdate. Most significantly, the mutant strain showed reduced virulence compared to wild-type strain PAO1 according to a competitive index in the rat model of chronic lung infection and a predation assay with Dictyostelium discoideum amoebae. As the latter took place in aerobic conditions, the in vivo impact of the mutation in modA appears to extend beyond its effect on anaerobic growth.
These results support the modABC-encoded transporter as important for the pathogenesis of P. aeruginosa, and suggest that enzymatic machinery implicated in anaerobic growth during chronic lung infection in CF merits further investigation as a potential target for therapeutic intervention.
囊性纤维化（CF）患者慢性肺部感染中铜绿假单胞菌成功致病的机制尚不清楚。先前通过大鼠肺部的基因筛选发现modA基因与铜绿假单胞菌的体内竞争力有关。该基因编码转运蛋白ModABC的一个亚基，负责钼酸盐的细胞外摄取。这种化合物对包括硝酸还原酶在内的钼酶至关重要。由于已知CF慢性肺部感染期间会出现厌氧生长条件，钼酸盐转运蛋白的失活可能通过反硝化酶的失活来抑制细菌增殖。因此，我们对通过签名标签诱变获得的modA突变株（STM_modA）进行了表型特征分析，并在两种宿主模型中评估了其体内毒力。
STM_modA突变株实际上在厌氧生长方面存在缺陷，并且无法利用生长培养基中的硝酸盐进行厌氧呼吸。当培养基中添加钼酸盐时，细菌生长和硝酸盐利用得以恢复。最重要的是，根据慢性肺部感染大鼠模型中的竞争指数以及与盘基网柄菌变形虫的捕食试验，与野生型菌株PAO1相比，突变株的毒力降低。由于后者是在有氧条件下进行的，modA突变在体内的影响似乎超出了其对厌氧生长的影响。
这些结果支持ModABC编码的转运蛋白对铜绿假单胞菌的发病机制很重要，并表明CF慢性肺部感染期间参与厌氧生长的酶机制作为治疗干预的潜在靶点值得进一步研究。
