  Bacteria have remarkably robust cell shape control mechanisms. For example,
cell diameter only varies by a few percent across a population. MreB is
necessary for establishment and maintenance of rod shape although the mechanism
of shape control remains unknown. We perturbed MreB in two complimentary ways
to produce steady-state cell diameters over a wide range, from 790+/-30 nm to
1700+/-20 nm. To determine which properties of MreB are important for diameter
control, we correlated structural characteristics of fluorescently-tagged MreB
polymers with cell diameter by simultaneously analyzing 3-dimensional images of
MreB and cell shape. Our results indicate that the pitch angle of MreB
inversely correlates with cell diameter. Other correlations are not found to be
significant. These results demonstrate that the physical properties of MreB
filaments are important for shape control and support a model in which MreB
dictates cell diameter and organizes cell wall growth to produce a chiral cell
wall.
