Pseudomonas aeruginosa colonizes the airways of cystic fibrosis (CF) patients, causing infections that can last for decades. During the course of these infections, P. aeruginosa undergoes a number of genetic adaptations. One such adaptation is the loss of swimming motility functions. Another involves the formation of the rugose small colony variant (RSCV) phenotype, which is characterized by overproduction of the exopolysaccharides Pel and Psl. Here, we provide evidence that the two adaptations are linked. Using random transposon mutagenesis, we discovered that flagellar mutations are linked to the RSCV phenotype. We found that flagellar mutants overexpressed Pel and Psl in a surface-contact dependent manner. Genetic analyses revealed that flagellar mutants were selected for at high frequencies in biofilms, and that Pel and Psl expression provided the primary fitness benefit in this environment. Suppressor mutagenesis of flagellar RSCVs indicated that Psl overexpression required the mot genes, suggesting that the flagellum stator proteins function in a surface-dependent regulatory pathway for exopolysaccharide biosynthesis. Finally, we identified flagellar mutant RSCVs among CF isolates. The CF environment has long been known to select for flagellar mutants, with the classic interpretation being that the fitness benefit gained relates to an impairment of the host immune system to target a bacterium lacking a flagellum. Our new findings lead us to propose that exopolysaccharide production is a key gain-of-function phenotype that offers a new way to interpret the fitness benefits of these mutations.

铜绿假单胞菌定植在囊性纤维化（CF）患者的气道上，导致感染可持续数十年。在这些感染过程中，P。铜绿经历了许多遗传适应。一种这样的适应是游泳运动功能的丧失。另一个涉及皱纹小菌落变体（RSCV）表型的形成，其特征在于胞外多糖Pel和Psl的过量产生。在这里，我们提供了两种改编联系在一起的证据。使用随机转座子诱变，我们发现鞭毛突变与RSCV表型相关。我们发现鞭毛突变体以表面接触依赖性方式过表达Pel和Psl。遗传分析表明，在生物膜中高频选择了鞭毛突变体，并且Pel和Psl表达在这种环境下提供了主要的适应性益处。鞭毛RSCVs的抑制诱变表明，过度的Psl所需的MOT基因，表明鞭毛定子蛋白在胞外多糖生物合成的表面依赖性调节途径中起作用。最后，我们确定了CF分离物中的鞭毛突变RSCV。长期以来，已知CF环境会选择鞭毛突变体，经典的解释是，获得的适应性益处与针对缺乏鞭毛的细菌的宿主免疫系统的损害有关。我们的新发现促使我们提出，胞外多糖的产生是关键的功能获得表型，它提供了解释这些突变的适应性益处的新方法。