  Rod-like bacteria maintain their cylindrical shapes with remarkable precision
during growth. However, they are also capable to adapt their shapes to external
forces and constraints, for example by growing into narrow or curved
confinements. Despite being one of the simplest morphologies, we are still far
from a full understanding of how shape is robustly regulated, and how bacteria
obtain their near-perfect cylindrical shapes with excellent precision. However,
recent experimental and theoretical findings suggest that cell-wall geometry
and mechanical stress play important roles in regulating cell shape in rod-like
bacteria. We review our current understanding of the cell wall architecture and
the growth dynamics, and discuss possible candidates for regulatory cues of
shape regulation in the absence or presence of external constraints. Finally,
we suggest further future experimental and theoretical directions, which may
help to shed light on this fundamental problem.
