Rabani Amit, Ariel Gil, Be'er Avraham
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.
Department of Mathematics, Bar-Ilan University, Ramat Gan, Israel.
PLoS One. 2013 Dec 20;8(12):e83760. doi: 10.1371/journal.pone.0083760. eCollection 2013.
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.
多种运动性细菌在液体环境中生存或在表面定殖时会表现出集体运动。这些集体运动通常以连贯的动态集群为特征，数百个细胞会以相关的涡旋和喷射形式移动。此前，所有已知能形成这种运动的物种都具有杆状结构，这种结构通过空间位阻和流体动力学相互作用增强了有序性。在此，我们表明球形运动细菌粘质沙雷氏菌在悬浮液中生长时会表现出强大的集体动力学和相关的连贯运动。当细胞迁移到液滴的上表面时，它们会形成单层，并以涡旋和喷射的形式集体移动。在所有浓度下，细菌速度的分布近似于瑞利分布，其平均值以非单调方式依赖于浓度。我们还分析了其他动力学参数，如涡度和相关函数，并与同一菌株的杆状细菌进行了比较。我们的结果表明，自主推进的球形物体确实会形成复杂的有序集体运动。这为从细胞纵横比和细胞排列在自然界集体运动中的作用这一新视角打开了一扇门。
