Bacterial FtsZ protein forms phase‐separated condensates with its nucleoid‐associated inhibitor SlmA

Abstract Macromolecular condensation resulting from biologically regulated liquid–liquid phase separation is emerging as a mechanism to organize intracellular space in eukaryotes, with broad implications for cell physiology and pathology. Despite their small size, bacterial cells are also organized by proteins such as FtsZ, a tubulin homolog that assembles into a ring structure precisely at the cell midpoint and is required for cytokinesis. Here, we demonstrate that FtsZ can form crowding‐induced condensates, reminiscent of those observed for eukaryotic proteins. Formation of these FtsZ‐rich droplets occurs when FtsZ is bound to SlmA, a spatial regulator of FtsZ that antagonizes polymerization, while also binding to specific sites on chromosomal DNA. The resulting condensates are dynamic, allowing FtsZ to undergo GTP‐driven assembly to form protein fibers. They are sensitive to compartmentalization and to the presence of a membrane boundary in cell mimetic systems. This is a novel example of a bacterial nucleoprotein complex exhibiting condensation into liquid droplets, suggesting that phase separation may also play a functional role in the spatiotemporal organization of essential bacterial processes.