Abstract
The Gram-positive bacterium Bacillus subtilis can divide via two modes. During vegetative growth, the division septum is formed at the midcell to produce two equal daughter cells. However, during sporulation, the division septum is formed closer to one pole to yield a smaller forespore and a larger mother cell. Using cryo-electron tomography, genetics and fluorescence microscopy, we found that the organization of the division machinery is different in the two septa. While FtsAZ filaments, the major orchestrators of bacterial cell division, are present uniformly around the leading edge of the invaginating vegetative septa, they are only present on the mother cell side of the invaginating sporulation septa. We provide evidence suggesting that the different distribution and number of FtsAZ filaments impact septal thickness, causing vegetative septa to be thicker than sporulation septa already during constriction. Finally, we show that a sporulation-specific protein, SpoIIE, regulates asymmetric divisome localization and septal thickness during sporulation.
Highlights
Bacterial cell division involves the invagination of the cellular membrane(s) and peptidoglycan (PG) cell wall to split the cell into two progeny cells
We show that a sporulation-specific protein, SpoIIE, regulates asymmetric divisome localization and septal thickness during sporulation. 26 Keywords B. subtilis, cell division, FtsZ, FtsA, SpoIIE, peptidoglycan, cryo-electron tomography, cryo-focused ion beam milling
We show that a sporulation-specific protein SpoIIE, which is essential for cell-specific gene expression after polar septation, is essential for the asymmetric assembly of FtsAZ filaments and septal thickness at the onset of sporulation (Figure 8,9)
Summary
The division septum is formed at the midcell to produce two equal daughter cells. During sporulation, the division septum is formed closer to one pole to yield a smaller forespore and a larger mother cell. Using cryo-electron tomography, genetics and fluorescence microscopy, we found that the organization of the division machinery is different in the two septa. While FtsAZ filaments, the major orchestrators of bacterial cell division, are present uniformly around the leading edge of the invaginating vegetative septa, they are only present on the mother cell side of the invaginating sporulation septa. We provide evidence suggesting that the different distribution and number of FtsAZ filaments impact septal thickness, causing vegetative septa to be thicker than sporulation septa already during constriction. 26 Keywords B. subtilis, cell division, FtsZ, FtsA, SpoIIE, peptidoglycan, cryo-electron tomography, cryo-focused ion beam milling We show that a sporulation-specific protein, SpoIIE, regulates asymmetric divisome localization and septal thickness during sporulation. 26 Keywords B. subtilis, cell division, FtsZ, FtsA, SpoIIE, peptidoglycan, cryo-electron tomography, cryo-focused ion beam milling
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