Role of FlhF and its domains in the assembly of a polar flagellum in <i>P. aeruginosa</i>

FlhF, an SRP GTPase, regulates the polarity and flagellation patterns in various bacteria, including <i>Pseudomonas aeruginosa</i>. FlhF is a multidomain protein that comprises three domains: B, N, and G, or the GTPase domain. However, the roles of different domains in the assembly and maintenance of flagella in this clinically important bacterium remain unclear. In this study, we report that the C-terminal GTPase domain plays a critical role in maintaining the polar localization of FlhF. Complementation assays using truncated constructs show that the flagellar assembly depends on both the B- and N-domains. In addition, GTP binding by FlhF regulates its interaction with FliG, a flagellar C-ring protein that facilitates flagellar basal body assembly in <i>P. aeruginosa</i>.IMPORTANCEPathogenic bacteria rely on flagellar motility for infection and colonization. FlhF, a member of the SRP GTPase family, is a key factor regulating flagellation patterns in various bacteria. In this study, we investigated the domain-wise role of FlhF in <i>P. aeruginosa,</i> an <i>ESKAPE</i> pathogen that uses a single flagellum for its virulence, biofilm formation, and pathogenesis. Our study reveals the role of FlhF in the assembly and spatial regulation of flagella in <i>P. aeruginosa</i>. In addition, we examined the interaction of FlhF with the flagellar ring protein. This study provides insights into the molecular mechanism underlying polar assembly of flagella, thus offering a targeted approach for controlling infection by this pathogen.