article epub_ahead yes Paula P. Navarro author Andrea Vettiger author Roman Hajdu author ffab949d-133f-11ed-8f02-94de21ace503 Virly Y. Ananda author Alejandro López-Tavares author Ernst W. Schmid author Johannes C. Walter author Martin Loose author 462D4284-F248-11E8-B48F-1D18A9856A870000-0001-7309-9724 Luke H. Chao author Thomas G. Bernhardt author MaLo department GradSch department The divisome apparatus synthesizes septal peptidoglycan (PG) during bacterial division. In Escherichia coli, the class A penicillin-binding protein (aPBP) called PBP1b has been implicated in division, but its role in the process has remained unclear. Here we show using in situ cryo-electron tomography, genetics and other imaging methods that PBP1b is required to produce a wedge-like density of PG at the division site and that loss of this structure weakens the division site, making it hypersusceptible to osmotic lysis. Surprisingly, the activator LpoB needed for general PBP1b function was not required for its role in division. Of the two PBP1b isoforms produced in cells, we show that the one with an extended cytoplasmic N terminus localizes to and functions at the division site, probably via recruitment by the FtsA component of the divisome. The conservation of aPBPs with extended cytoplasmic N termini suggests that other Gram-negative bacteria may use similar mechanisms for division site reinforcement. Springer Nature2026 eng 2058-5276 4239956110.1038/s41564-026-02403-6 Navarro PP, Vettiger A, Hajdu R, et al. The penicillin-binding protein PBP1b fortifies the Escherichia coli division site against osmotic rupture. <i>Nature Microbiology</i>. 2026. doi:<a href="https://doi.org/10.1038/s41564-026-02403-6">10.1038/s41564-026-02403-6</a> P. P. Navarro <i>et al.</i>, “The penicillin-binding protein PBP1b fortifies the Escherichia coli division site against osmotic rupture,” <i>Nature Microbiology</i>. Springer Nature, 2026. Navarro, Paula P., Andrea Vettiger, Roman Hajdu, Virly Y. Ananda, Alejandro López-Tavares, Ernst W. Schmid, Johannes C. Walter, Martin Loose, Luke H. Chao, and Thomas G. Bernhardt. “The Penicillin-Binding Protein PBP1b Fortifies the Escherichia Coli Division Site against Osmotic Rupture.” <i>Nature Microbiology</i>. Springer Nature, 2026. <a href="https://doi.org/10.1038/s41564-026-02403-6">https://doi.org/10.1038/s41564-026-02403-6</a>. Navarro, P. P., Vettiger, A., Hajdu, R., Ananda, V. Y., López-Tavares, A., Schmid, E. W., … Bernhardt, T. G. (2026). The penicillin-binding protein PBP1b fortifies the Escherichia coli division site against osmotic rupture. <i>Nature Microbiology</i>. Springer Nature. <a href="https://doi.org/10.1038/s41564-026-02403-6">https://doi.org/10.1038/s41564-026-02403-6</a> Navarro PP, Vettiger A, Hajdu R, Ananda VY, López-Tavares A, Schmid EW, Walter JC, Loose M, Chao LH, Bernhardt TG. 2026. The penicillin-binding protein PBP1b fortifies the Escherichia coli division site against osmotic rupture. Nature Microbiology. P.P. Navarro, A. Vettiger, R. Hajdu, V.Y. Ananda, A. López-Tavares, E.W. Schmid, J.C. Walter, M. Loose, L.H. Chao, T.G. Bernhardt, Nature Microbiology (2026). Navarro, Paula P., et al. “The Penicillin-Binding Protein PBP1b Fortifies the Escherichia Coli Division Site against Osmotic Rupture.” <i>Nature Microbiology</i>, Springer Nature, 2026, doi:<a href="https://doi.org/10.1038/s41564-026-02403-6">10.1038/s41564-026-02403-6</a>. 222692026-07-12T22:02:19Z2026-07-13T09:22:49Z