<scp>FlhG</scp> Cooperates With the Cell Cycle Regulator <scp>GpsB</scp> to Confine Peritrichous Flagella in <scp><i>B. subtilis</i></scp>

Number and arrangement of flagella, the bacterial locomotion organelles, are species-specific and serve as key taxonomic markers. The FlhG ATPase (also: YlxH, FleN), along with FlhF, plays pivotal roles in determining flagellation patterns. In Bacillus subtilis , FlhG and FlhF govern the spatial arrangement of peritrichous flagella. FlhG aids in flagellar assembly by interacting with the flagellar C-ring protein FliY, yet the molecular implications of this interaction have been unclear. Our study reveals that the ATP-dependent FlhG homodimer interacts with the C-terminal domain of GpsB, a cell cycle regulator, which recruits the peptidoglycan synthase PBP1 (also: ponA) to sites of cell wall elongation. A deletion of gpsB leads to dysregulation of the flagellation pattern mimicking the effects of a flhG deletion strain. The finding that GpsB can interact simultaneously with FlhG and PBP1, combined with the observation that GpsB and FliY can simultaneously interact with FlhG, strongly argues for a model in which FlhG confines flagella biosynthesis to regions of active cell wall biosynthesis. Thus, the FlhG-GpsB interaction appears to enable the locally restrained stimulation of the GTPase FlhF, known for its role to localize flagella in various bacterial species.