Pseudomonas aeruginosa is a cause of chronic respiratory tract infections in people with cystic fibrosis (CF), non-CF bronchiectasis and chronic obstructive pulmonary disease. Prolonged infection allows accumulation of mutations and horizontal gene transfer, increasing the likelihood of adaptive phenotypic traits. Adaptation is proposed to arise first in bacterial populations colonising upper airway environments. Here, we model this process using an experimental evolution approach. P. aeruginosa PAO1, which is not airway adapted, was serially passaged, separately, in media chemically reflective of upper or lower airway environments. To explore whether the CF environment selects for unique traits, we separately passaged PAO1 in airway-mimicking media with or without CF-specific factors. Our findings demonstrated that all airway environments – sinus and lungs, under CF and non-CF conditions – selected for loss of twitching motility, increased resistance to multiple antibiotic classes and a hyper-biofilm phenotype. These traits conferred increased airway colonisation potential in an in vivo model. CF-like conditions exerted stronger selective pressures, leading to emergence of more pronounced phenotypes. Loss of twitching was associated with mutations in type IV pili genes. Type IV pili mediate surface attachment, twitching and induction of cAMP signalling. We additionally identified multiple evolutionary routes to increased biofilm formation involving regulation of cyclic-di-GMP signalling. These included loss of function mutations in bifA and dipA phosphodiesterase genes and activating mutations in the siaA phosphatase. These data highlight that airway environments select for traits associated with sessile lifestyles and suggest upper airway niches support emergence of phenotypes that promote establishment of lung infection.

中文翻译：

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第二信使信号影响铜绿假单胞菌对鼻窦和肺部环境的适应

铜绿假单胞菌是囊性纤维化 (CF)、非 CF 支气管扩张和慢性阻塞性肺病患者慢性呼吸道感染的原因。长时间的感染会导致突变的积累和水平基因转移，从而增加适应性表型特征的可能性。适应首先出现在上呼吸道环境中定殖的细菌群体中。在这里，我们使用实验进化方法对这个过程进行建模。铜绿假单胞菌PAO1不适应气道，在化学反映上气道或下气道环境的培养基中单独连续传代。为了探讨 CF 环境是否选择独特的性状，我们分别在有或没有 CF 特异性因子的气道模拟培养基中传代 PAO1。我们的研究结果表明，所有气道环境（鼻窦和肺部，在 CF 和非 CF 条件下）都选择了抽搐运动丧失、对多种抗生素类别的耐药性增加和超生物膜表型。这些特征赋予了体内模型中气道定植潜力的增加。类似 CF 的条件施加了更强的选择压力，导致出现更明显的表型。抽搐的丧失与 IV 型菌毛基因的突变有关。 IV 型菌毛介导表面附着、抽搐和 cAMP 信号传导。我们还确定了增加生物膜形成的多种进化途径，涉及环二 GMP 信号传导的调节。这些包括bifA和dipA磷酸二酯酶基因的功能缺失突变以及siaA磷酸酶的激活突变。这些数据强调，气道环境选择与固着生活方式相关的特征，并表明上气道生态位支持促进肺部感染建立的表型的出现。