Fig. 1. FtsZ overexpression exacerbates branching in LMW PBP mutants.

E. coli CS315-1, which lacks PBPs 4, 5 and 7, harboring plasmids pBR322 (A, D) pZAQ (B, E) and pLPZ (C, F), were grown in LB-Tet medium until they reached an OD₆₀₀ of 0.2. At this OD, cells were either harvested for microscopy (A, B, C) or were further grown for one mass doubling (MD) in the presence of 1 µg/ml of aztreonam to filament the cells (D, E, F). Panels A–C and D–F have different magnifications. The scale bars in panels A–C denote 5 µm and in panels D–F denote 10 µm. Panel G shows the percentage of cells with branches, including single and multiple protrusions. Panel H shows the percentage of cells with multiple branches (more than 3 poles per cell). In panels G and H, the percentage of branched cells in different strains harboring pBR322, pZAQ and pLPZ plasmids are represented by light, grey and black bars, respectively. At least 500 cells were counted for each strain. Panels G and H represent results averaged from two independent experiments.