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

13 p.-6 fig.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.This work was supported by the Fondo Europeo de Desarrollo Regional (FEDER) and the Agencia Estatal de Investigación (AEI); by the Spanish government (BFU2014-52070-C2-2-P and BFU2016-75471-C2-1-P, G. R.); by the National Institutes of Health (GM61074, W. M.); and by the National Science Foundation (MCB-1715984,C. D. K.). M.L.-A. was supported by the European Social Fund (ESF 2014-2020).Peer reviewe