Dynamics of swimming bacteria: Transition to directional order at high concentration
Dynamics of swimming bacteria: Transition to directional order at high concentration
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DOI：
10.1103/physreve.83.061907
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发表时间：
2011-06-14
影响因子：
2.4
通讯作者：
Goldstein, Raymond E.
中科院分区：
文献类型：
--
作者：
Cisneros, Luis H.;Kessler, John O.;Goldstein, Raymond E.
众所周知，在高细胞浓度下，细菌悬浮液会形成一种集体游泳的状态(“变焦生物相”，或ZBN)，其特征是瞬时的、反复的协调运动区域，远远超过单个细胞的大小。最近对半稀悬浮液的理论研究表明，游动细胞之间的长程流体动力相互作用是导致这些模式的长波不稳定性的原因，而适用于较高浓度的模型则表明，拉长细胞之间的空间相互作用在自组织中起着重要作用。利用粒子成像测速技术，我们研究了枯草芽孢杆菌悬浮液中向ZBN转变的统计特性，特别是细胞游动速度的分布及其与取向顺序的关联。这一分析揭示了平均细胞游泳速度与细胞浓度之间的非单调关系，在向ZBN过渡的过程中出现最小值。在ZBN阶段，高取向有序的区域具有局部较高的游泳速度，而取向无序的区域具有较低的速度。用浓缩悬浮液中空间位阻相互作用的模型和以前观察到的鞭毛反弹动力学与游泳方向的变化来解释这一观察结果。强调了在理论模型中考虑空间位阻对细胞游动的影响的必要性。
At high cell concentrations, bacterial suspensions are known to develop a state of collective swimming (the "zooming bionematic phase," or ZBN) characterized by transient, recurring regions of coordinated motion greatly exceeding the size of individual cells. Recent theoretical studies of semidilute suspensions have suggested that long-range hydrodynamic interactions between swimming cells are responsible for long-wavelength instabilities that lead to these patterns, while models appropriate for higher concentrations have suggested that steric interactions between elongated cells play an important role in the self-organization. Using particle imaging velocimetry in well-defined microgeometries, we examine the statistical properties of the transition to the ZBN in suspensions of Bacillus subtilis, with particular emphasis on the distribution of cell swimming speeds and its correlation with orientational order. This analysis reveals a nonmonotonic relationship between mean cell swimming speed and cell concentration, with a minimum occurring near the transition to the ZBN. Regions of high orientational order in the ZBN phase have locally high swimming speeds, while orientationally disordered regions have lower speeds. A model for steric interactions in concentrated suspensions and previous observations on the kinetics of flagellar rebundling associated with changes in swimming direction are used to explain this observation. The necessity of incorporating steric effects on cell swimming in theoretical models is emphasized.