Abstract
Rod-shaped bacteria direct cell division by assembling cytoskeletal polymers into a treadmillingring known as the Z-ring at the site of the future septum. The position of this ring and the thickness
of the resulting septum are specific to different developmental fates. In the endospore-forming
bacterium Bacillus subtilis, the conserved sporulation protein SpoIIE plays a crucial role in
repositioning the midcell division machinery toward the cell poles and generating a thin septum.
However, the precise mechanisms by which SpoIIE accomplishes this are not fully understood.
Using live-cell total internal fluorescence microscopy (TIRFm), we show that SpoIIE moves with
the dynamic Z-ring. Through further genetic and biochemical approaches, we identify multiple
interactions of SpoIIE, first with midcell placement factors MinC/D and later with the cell wall
synthesis regulator DivIB, that are essential for sporulation septum morphology. This work reveals
that SpoIIE has dissectible roles in 1) regulating the length of FtsZ filaments within the Z-ring, 2)
opposing MinC/D, and 3) promoting cytokinesis. We find that the cytosolic portion of SpoIIE is
responsible for Z-ring association and Min opposition, while the large transmembrane domain is
required for Z-ring constriction and recruitment of DivIB. In addition to answering longstanding
questions about how SpoIIE coordinates asymmetric cell division in sporulation, this work begins
to explain the broader mechanisms by which cells relate Z-ring structure to the regulation of cell
wall synthesis.