title: Collective motion of spherical bacteria.
abstract: A large variety of motile bacterial species exhibit collective motions while inhabiting liquids or colonizing surfaces. These collective motions are often characterized by coherent dynamic clusters, where hundreds of cells move in correlated whirls and jets. Previously, all species that were known to form such motion had a rod-shaped structure, which enhances the order through steric and hydrodynamic interactions. Here we show that the spherical motile bacteria Serratia marcescens exhibit robust collective dynamics and correlated coherent motion while grown in suspensions. As cells migrate to the upper surface of a drop, they form a monolayer, and move collectively in whirls and jets. At all concentrations, the distribution of the bacterial speed was approximately Rayleigh with an average that depends on concentration in a non-monotonic way. Other dynamical parameters such as vorticity and correlation functions are also analyzed and compared to rod-shaped bacteria from the same strain. Our results demonstrate that self-propelled spherical objects do form complex ordered collective motion. This opens a door for a new perspective on the role of cell aspect ratio and alignment of cells with regards to collective motion in nature.
authors.affiliation: Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, Midreshet Ben-Gurion, Israel.
authors.forename: Amit
authors.initials: A
authors.lastname: Rabani
authors.affiliation: Department of Mathematics, Bar-Ilan University, Ramat Gan, Israel.
authors.forename: Gil
authors.initials: G
authors.lastname: Ariel
authors.affiliation: Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, Midreshet Ben-Gurion, Israel.
authors.forename: Avraham
authors.initials: A
authors.lastname: Be'er
mesh_terms: D009068:Movement; D012706:Serratia marcescens / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D062211:Spatio-Temporal Analysis; D013501:Surface-Active Agents / Q000378:metabolism
chemical_list: D013501:Surface-Active Agents