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Edited by Joe Lutkenhaus, University of Kansas Medical Center, Kansas City, KS, and approved November 24, 2020 (received for review February 11, 2020)
Significance
Many bacteria form a thick cell wall and divide by forming a cross wall. How they control the thickness of their cell wall and cross wall is unknown. In this study, we show that in these bacteria the cell division protein SepF forms very large protein rings with diameters that correspond to the diameter of their cross walls. Importantly, when we changed the diameter of SepF rings in the bacterial host Bacillus subtilis, the thickness of its cross wall changed accordingly. These results provide strong evidence that a large protein ring can function as a mold to control the thickness of the cell wall that divides these bacterial cells.
Abstract
Gram-positive bacteria divide by forming a thick cross wall. How the thickness of this septal wall is controlled is unknown. In this type of bacteria, the key cell division protein FtsZ is anchored to the cell membrane by two proteins, FtsA and/or SepF. We have isolated SepF homologs from different bacterial species and found that they all polymerize into large protein rings with diameters varying from 19 to 44 nm. Interestingly, these values correlated well with the thickness of their septa. To test whether ring diameter determines septal thickness, we tried to construct different SepF chimeras with the purpose to manipulate the diameter of the SepF protein ring. This was indeed possible and confirmed that the conserved core domain of SepF regulates ring diameter. Importantly, when SepF chimeras with different diameters were expressed in the bacterial host Bacillus subtilis, the thickness of its septa changed accordingly. These results strongly support a model in which septal thickness is controlled by curved molecular clamps formed by SepF polymers attached to the leading edge of nascent septa. This also implies that the intrinsic shape of a protein polymer can function as a mold to shape the cell wall.
Footnotes
↵1Present address: Division of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
↵2M.W. and I.N.C.G. contributed equally to this work.
↵3Present address: Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115.
- ↵4To whom correspondence may be addressed. Email: l.w.hamoen{at}uva.nl.
Author contributions: M.W. and L.W.H. designed research; M.W., I.N.C.G., Y.G., Z.T., J.W., M.M., M.G.M.v.R., P.W.B.L., N.N.v.d.W., G.J.L.W., and W.H.R. performed research; M.W., I.N.C.G., Y.G., Z.T., J.W., M.M., M.G.M.v.R., P.W.B.L., N.N.v.d.W., G.J.L.W., W.H.R., and L.W.H. analyzed data; and M.W. and L.W.H. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2002635118/-/DCSupplemental.
Data Availability.
All study data are included in the article and supporting information.
Published under the PNAS license.
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Control of septum thickness by the curvature of SepF polymers
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- Microbiology
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