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.
Highlights
Motility is a fundamental function of bacteria required for survival in response to environmental changes
To summarize all the insights presented in this review, we would like to propose a model for the biogenesis of a single polar flagellum in Vibrio alginolyticus (Figure 8)
At least five factors are involved in this precise control: FlhF, FlhG, HubP, FlaK, and SflA
Summary
Motility is a fundamental function of bacteria required for survival in response to environmental changes. The marine bacterium Vibrio alginolyticus, which generates a single flagellum at its cell pole in a liquid environment [23], is a good model organism because genetic, biochemical, and structural analyses of its polar flagellar system have been extensively studied [4]. The filament of the polar flagellum is covered with a membranous sheath contiguous with the outer membrane of the bacterial cell [24], and because of its thickness it can be observed using high intensity dark-field microscopy [25] Using this bacterium, our group has reported that two key factors, FlhF and FlhG, Biomolecules 2020, 10, 533 play major roles in the regulation of polar flagellar number and placement. All of our studies described in this review used bacterial strains that do not produce lateral flagella (VIO5 [27] and its derivatives)
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