A phase-separated biomolecular condensate nucleates polymerization of the tubulin homolog FtsZ to spatiotemporally regulate bacterial cell division

Cell division is spatiotemporally precisely regulated, but the underlying mechanisms are incompletely understood. In the social, predatory bacterium Myxococcus xanthus, the PomX/PomY/PomZ proteins form a single large megadalton-sized complex that directly positions and stimulates cytokinetic ring formation by the tubulin homolog FtsZ. Here, we studied the structure and mechanism of this complex in vitro and in vivo. We demonstrate that PomY forms liquid-like biomolecular condensates by phase separation, while PomX self-assembles into filaments generating a single large cellular structure. The PomX structure enriches PomY, thereby guaranteeing the formation of precisely one PomY condensate per cell through surface-assisted condensation. In vitro, PomY condensates selectively enrich FtsZ and nucleate GTP-dependent FtsZ polymerization, suggesting a novel cell division site positioning mechanism in which the single PomY condensate enriches FtsZ to guide FtsZ-ring formation and division. PomY-nucleated FtsZ polymerization shares features with microtubule nucleation by biomolecular condensates in eukaryotes, supporting this mechanisms ancient origin.