FIG 1.
Curved sheath polymerization guided by membrane contact. (A) Sheath assembly in the VipA-sfGFP-labeled strain treated with ampicillin. The image at the left is of a merge of the phase and GFP (green) channels. The images in the series correspond to 5-min time-lapse videos (10 s per frame). Scale bar, 1 μm. Additional examples can be found in Fig. S1A and Movie S1 in the supplemental material. (B) Temporal color-coded image corresponding to sheath polymerization (0 to 200 s) of the cell depicted in panel A. The color code (spectrum) and time scale are shown at the bottom of the panel. (C) Model of initially straight sheath (green) followed by curved polymerization. Green cylinders represent sheath subunits. The scatterplot on the right shows the ratio of the initial straight length of the sheath (lS) over the total curvy length of the sheath (lC), measured for 30 sheaths. (D) Images show precontraction and contraction and disassembly of curved sheaths formed by the VipA-sfGFP-labeled ampicillin (Amp)-treated cells (top panel) and mrcA deletion cells (bottom panel). The panels at the left represent merges of the phase and green (GFP) channels. All images are representative examples of results from at least three biological replicates. Scale bars, 1 μm. (E and F) Sheath length (E) and average curvature (calculated using Kappa) (F) of sheaths formed in ampicillin-treated (n = 80) and mrcA deletion (n = 40) spheroplasts and rod cells (n = 150). Each data point represents an independent biological replicate. Graphs show mean values (bars) ± SD (lines). ns, nonsignificant; *, P < 0.05 (unpaired t test); Wt, wild type.