GSE30810
Role of FliL in Swarmer Cell Differentiation
Proteus mirabilis is an opportunistic pathogen that causes urinary tract infections in immunocompromised patients. Flagellar motility coupled with the ability to differentiate from short swimmer cells to highly elongated swarmer cells constitute key parts of the infection process. The mechanism by which the cells transduce the signal to differentiate remains unknown, but is believed to involve inhibition of flagellar rotation. Recent work has implicated FliL as a critical component of the signal transduction process, possibly through interactions with the motor proteins. The objective in the current study was to define the molecular mechanism underlying the cellâ??s ability to perceive a surface and begin the differentiation process, with a specific emphasis as to the role of FliL. Thus, the deep-sequencing technology of RNA-Seq was combined with genetic analysis to further examine the role of FliL in swarmer cell differentiation. RNA-Seq analysis of wild-type swarmer cells confirmed prior reports of genes involved in the differentiation process while concomittantly identifying novel genes potentially involved in swarming (including PMI1628, PMI0714-0716, and PMI0735, PMI0737, PMI0739, and PMI0740-0734). In comparison, RNA-Seq analysis of a fliL mutant showed that nearly all genes associated with the flagellar cascade and chemotaxis are repressed. A phenotypic, genetic, and transcriptomic characterization was then performed on spontaneous revertants of the fliL mutant, in which motility was restored yet still resulted in cells that differentiated under non-inducing (i.e. broth) conditions. Sequencing revealed perturbations in the C-terminus of FliL in both the mutant and revertant. Collectively, the data suggest that FliL senses the torque applied to the motor proteins- such as is encountered by a solid surface - and relays this signal to the master flagellar regulator FlhD4C2, triggering the expression of genes involved in the flagellar cascade. Overall design: Transcriptomic comparison between wild-type Proteus mirabilis swarmer cells and a fliL mutant via RNA-Seq.