Modeling helical shape formation in bacteria

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 mechanism of helix formation 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 highly depend on the initial helical angle of the reinforced region. We find that steep angles may result in crooked helices with reduced end to end distance upon pressurization. This provides a possible mechanism for active shape transformations due to local osmolarity changes and may also inspire the design of novel pressure-controlled helical actuators.