The spatial organization of the Z-ring, the central element of the bacterial division machinery, is not yet fully understood. We have used optical tweezers and subpixel image analysis to estimate D, the radial width of the Z-ring in E. coli. Rod-shaped bacterial cells were trapped and rotated with respect to the optical axis with single-beam, oscillating Optical Tweezers. The angle of rotation is determined by the amplitude of the oscillation [1]. This technique allows imaging of fluorescently labeled 3D sub-cellular structures from different, optimized viewpoints. We used unconstricted cells with a mature Z-ring that was visualized via FtsZ-GFP and stained the cytoplasmic membrane with FM4-64. In a vertically oriented cell, both the Z-ring and the cytoplasmic membrane images appear as symmetric circular structures that lend themselves to quantitative analysis. We found that D≈100 nm [2]. The relatively large width is consistent with the observations of others. Moreover, simulation of the experimental FtsZ distribution using the theoretical 3D point spread function was strongly in favor of a toroidal rather than a thin cylindrical  model of the Z-ring. Since the amount of FtsZ in the Z-ring is limited, our findings suggest that the Z-ring consists of a sparse, multilayered network of FtsZ filaments. 

1. G. Carmon and M. Feingold, 2011, Rotation of single bacterial cells relative to the optical axis using Optical Tweezers, Opt. Lett. 36, 40-42.

2. G. Carmon, I. Fishov and M. Feingold, 2012, Oriented imaging of 3D sub-cellular structures in bacterial cells using Optical Tweezers, Opt. Lett. 37, 440-42.