MinD-like ATPase FlhG synchronizes flagellation and cell division in spirochetes

ABSTRACT Spirochetes are evolutionarily distinct bacteria defined by their spiral morphology, unique means of motility, and periplasmic flagella (PFs). Because these flagella reside within the periplasm and are mechanically integrated with the cell body, their assembly must be precisely coordinated with cell growth and cytokinesis. However, the mechanism coupling flagellar biogenesis to cell division in spirochetes remains unclear. Using the Lyme disease spirochete Borrelia burgdorferi as a model, we identify FlhG (BB0269), a MinD-like ATPase, as a spatial regulator that links cell division to flagellar patterning. In wild-type cells, 7–11 long helical PFs form at each pole and form ribbon-like bundles that wrap around the cell cylinder to drive motility. Deletion of flhG disrupts this ordered architecture, resulting in pronounced heterogeneity in flagellar number, defective ribbon formation, aberrant septation, and severe motility defects. Mechanistically, FlhG dynamically localizes to the poles and division site, where it spatially organizes FlhF, an SRP-type GTPase that controls flagellar number and positioning, and FliF, the MS-ring protein that is an essential early component for flagellar biogenesis. Through this spatial regulation, FlhG coordinates flagellar biogenesis with cytokinetic progression. Together, these findings uncover a spatial regulatory mechanism that couples cell division to flagellation, providing insight into how spirochetes coordinate morphogenesis and motility to maintain their distinctive cellular architecture. IMPORTANCE Spirochetes such as Borrelia burgdorferi , the causative agent of Lyme disease, rely on periplasmic flagella for motility and cell shape, yet how these structures are coordinated with cell division has remained unclear. We identify a MinD-like ATPase, FlhG, as a spatial regulator that couples flagellar assembly to cytokinesis. In contrast to its homologs in most bacteria, FlhG does not regulate flagellar protein levels but instead directs subcellular positioning of key assembly factors. By dynamically redistributing between the cell poles and division site, FlhG synchronizes flagellar patterning with septum formation. These findings uncover a previously unrecognized mechanism linking cell morphogenesis to the cell cycle and reveal how conserved ATPases can be repurposed to organize complex bacterial architectures.