Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology, 2628 CD Delft, the Netherlands.
Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology, 2628 CD Delft, the Netherlands
Proc Natl Acad Sci U S A. 2021 May 18;118(20). doi: 10.1073/pnas.2102095118.
The accumulation of motile cells at solid interfaces increases the rate of surface encounters and the likelihood of surface attachment, leading to surface colonization and biofilm formation. The cell density distribution in the vicinity of a physical boundary is influenced by the interactions between the microswimmers and their physical environment, including hydrodynamic and steric interactions, as well as by stochastic effects. Disentangling the contributions of these effects remains an experimental challenge. Here, we use a custom-made four-camera view microscope to track a population of motile puller-type in a relatively unconstrained three-dimensional (3D) domain. Our experiments yield an extensive sample of 3D trajectories including cell-surface encounters with a planar wall, from which we extract a full description of the dynamics and the stochasticity of swimming cells. We use this large data sample and combine it with Monte Carlo simulations to determine the link between the dynamics at the single-cell level and the cell density. Our experiments demonstrate that the near-wall scattering is bimodal, corresponding to steric and hydrodynamic effects. We find, however, that this near-wall dynamics has little influence on the cell accumulation at the surface. On the other hand, we present evidence of a cell-induced surface-directed rotation leading to a vertical orbiting behavior and hopping trajectories, consistent with long-range hydrodynamic effects. We identify this long-range effect to be at the origin of the significant surface accumulation of cells.
游动细胞在固体界面上的聚集增加了表面相遇的速率和表面附着的可能性，从而导致表面定殖和生物膜的形成。物理边界附近的细胞密度分布受到微游动器与其物理环境之间相互作用的影响，包括水动力和空间相互作用，以及随机效应。分离这些效应的贡献仍然是一个实验挑战。在这里，我们使用定制的四相机视图显微镜在相对不受限制的三维（3D）域中跟踪游动的拉动力型细胞群体。我们的实验产生了大量的 3D 轨迹，包括与平面壁的细胞表面相遇，从中我们提取了游动细胞动力学和随机性的完整描述。我们使用这个大数据样本并结合蒙特卡罗模拟来确定单细胞水平的动力学与细胞密度之间的联系。我们的实验表明，近壁散射呈双峰分布，对应于空间和水动力效应。然而，我们发现这种近壁动力学对表面上的细胞聚集几乎没有影响。另一方面，我们提出了证据表明细胞诱导的表面定向旋转导致垂直轨道运动和跳跃轨迹，与长程水动力效应一致。我们将这种长程效应确定为细胞在表面上显著积累的原因。
