Regulation of the Single Polar Flagellar Biogenesis

Abstract

Some bacterial species, such as the marine bacterium Vibrio alginolyticus, have a single polar flagellum that allows it to swim in liquid environments. Two regulators, FlhF and FlhG, function antagonistically to generate only one flagellum at the cell pole. FlhF, a signal recognition particle (SRP)-type guanosine triphosphate (GTP)ase, works as a positive regulator for flagellar biogenesis and determines the location of flagellar assembly at the pole, whereas FlhG, a MinD-type ATPase, works as a negative regulator that inhibits flagellar formation. FlhF intrinsically localizes at the cell pole, and guanosine triphosphate (GTP) binding to FlhF is critical for its polar localization and flagellation. FlhG also localizes at the cell pole via the polar landmark protein HubP to directly inhibit FlhF function at the cell pole, and this localization depends on ATP binding to FlhG. However, the detailed regulatory mechanisms involved, played by FlhF and FlhG as the major factors, remain largely unknown. This article reviews recent studies that highlight the post-translational regulation mechanism that allows the synthesis of only a single flagellum at the cell pole.

Interdependent Polar Localization of FlhF and FlhG and Their Importance for Flagellum Formation of Vibrio parahaemolyticus

“…Polar localization of FlhG was strictly dependent on the cell pole-determinant HubP, while polar localization of FlhF was HubP independent. This distinct dependency on HubP for their recruitment to the cell pole has been shown in other related bacterial organisms and Vibrio species as well (Kojima et al, 2020). This again supports the notion that FlhF and FlhG work in V. parahaemolyticus, in a manner similar to that reported in other Vibrio species.…”

“…It is essential to understand the mechanisms required for dissemination of bacteria in the environment and for many bacteria, the primary means of motion is flagella-mediated swimming motility. Correct swimming behavior heavily depends on the production of the correct number and proper placement of the flagella within the cell ( Schuhmacher et al, 2015b ; Blagotinsek et al, 2020 ; Kojima et al, 2020 ).…”

“…( Pandza et al, 2000 ; Murray and Kazmierczak, 2006 ) and S. putrefaciens ( Rossmann et al, 2015 ), where a single mislocalized non-polar flagellum is produced in the absence of FlhF. Importantly, FlhF is thought to establish the site of flagellum assembly by recruiting the earliest flagellar structural component FliF, which constitutes the MS-ring ( Green et al, 2009 ; Kojima et al, 2020 ; Terashima et al, 2020 ). Fluorescence microscopy studies have shown that FlhF is localized to the bacterial cell poles in several monotrichous bacterial species, including P. aeruginosa ( Murray and Kazmierczak, 2006 ), S. putrefaciens ( Rossmann et al, 2015 ), V. alginolyticus ( Kusumoto et al, 2008 ), and V. cholerae ( Green et al, 2009 ; Yamaichi et al, 2012 ; Takekawa et al, 2016 ).…”

“…In summary, many different bacteria use FlhF and FlhG to regulate the localization and positioning of their flagella. The system’s general function as positive and negative regulators of the flagellum synthesis, respectively, is largely conserved even among different bacterial phyla ( Schuhmacher et al, 2015b ; Kojima et al, 2020 ). Nevertheless, differences in the details of the system account for individual differences in the flagellar assembly even between members of the same genus ( Schuhmacher et al, 2015b ; Kojima et al, 2020 ).…”

Role of the N- and C-terminal regions of FliF, the MS ring component inVibrioflagellar basal body

“…The interaction to generate torque similarly occurs in the sodium-driven motor of V. alginolyticus (18)(19)(20). FlhG determining their position and number (21)(22)(23)(24). FlhF, which has a GTPase activity and is similar to the signal recognition particle protein Ffh which has a role in protein export, controls the number of flagella positively localized at the cell pole, to determine the position of the flagellum.…”