  Many bacterial species are helical in form, including the widespread pathogen
H. pylori. Motivated by recent experiments on H. pylori showing that cell wall
synthesis is not uniform, we investigate the possible formation of helical cell
shape induced by elastic heterogeneity. We show, experimentally and
theoretically, that helical morphogenesis can be produced by pressurizing an
elastic cylindrical vessel with helical reinforced lines. The properties of the
pressurized helix are highly dependent on the initial helical angle of the
reinforced region. We find that steep angles result in crooked helices with,
surprisingly, reduced end-to-end distance upon pressurization. This work helps
to explain the possible mechanisms for the generation of helical cell
morphologies and may inspire the design of novel pressure-controlled helical
actuators.
