A MinD-like ATPase couples 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 filaments 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 that couples 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 originate from cell poles and assemble into ribbon-like bundles that wrap around the cell cylinder to drive motility. Deletion of flhG disrupts this ordered architecture, causing marked heterogeneity in flagellar number, defective ribbon assembly, aberrant septation, and severe motility impairment. Mechanistically, FlhG dynamically localizes to the poles and midcell during division, where it directs the positioning of FlhF, a signal recognition particle (SRP) -type GTPase controlling flagellar number and placement, and FliF, the MS-ring protein that nucleates flagellar assembly. Through this spatial regulation, FlhG coordinates flagellar assembly with cytokinetic progression. Together, these findings reveal a spatial regulatory mechanism coupling cell division to flagellation, providing insight into understanding how spirochetes coordinate their distinctive morphogenesis, flagellation and motility. SignificanceSpirochetes 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 other 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.