E. coli LP18-1 (wild type) harboring pZAQ (A, B) or pLPZ (C, D), and E. coli LP1 (ΔPBPs 4, 5 and 7) harboring pZAQ (E, F) or pLPZ (G, H), were grown and imaged as described in Experimental Procedures. Cells in panels B, D, F and H were grown for 1 mass doubling in the presence of 1 µg/ml of aztreonam. The inset in panel B is an enlarged portion of the figure to show the FtsZ spirals more clearly. White arrows represent incomplete Z-rings and FtsZ arcs. All images have same magnification; the scale bar in panel A equals 5 µm.