Coordination between chromosome segregation and peptidoglycan remodeling during bacterial spore development

Asymmetric division during spore development generates a larger mother cell and a smaller forespore. Approximately 75% of the forespore chromosome must be translocated across the division septum into the forespore by the DNA translocase SpoIIIE. Asymmetric division also triggers cell-specific transcription, which initiates septal peptidoglycan remodeling involving synthetic and hydrolytic enzymes. How these processes are coordinated has remained a mystery. Using transposon-sequencing in Bacillus subtilis, we discovered factors underlying a critical coordination between chromosome translocation and peptidoglycan remodeling. Disrupting this coordination mechanism results in forespore cytoplasmic leakage and forespore chromosome efflux into the mother cell. Importantly, both phenotypes are prevented by abolishing or reducing the activity of septal peptidoglycan hydrolases. Remarkably, cells lacking this coordination mechanism and the SpoIIIAH-SpoIIQ transeptal interaction exhibit septal retraction, completely abolishing development. Localization of SpoIIIE within retracted septa suggest that it forms complexes within an enlarged septal pore. Our data indicate SpoIIIE translocates DNA at a highly stabilized septal pore that coordinates multiple developmental processes at once: the translocation of a chromosome across it, the maintenance of compartmentalization, and the dramatic remodeling of the forespore envelope. In this presentation I will share our published work revealing this coordination mechanism, and unpublished work in genetics, structural biology and biophysics that is yielding new insight into the complexity of this mechanism.