Shear-induced orientational dynamics and spatial heterogeneity in suspensions of motile phytoplankton

Fluid flow, ubiquitous in natural and man-made environments, has the potential to profoundly impact the transport of microorganisms, including phytoplankton in aquatic habitats and bioreactors. Yet, the effect of ambient flow on the swimming behavior of phytoplankton has remained poorly understood, largely due to the difficulty of observing cell-flow interactions at the microscale. Here, we present microfluidic experiments where we tracked individual cells for four species of motile phytoplankton exposed to a spatially non-uniform fluid shear rate, characteristic of many flows in natural and artificial environments. We observed that medium to high mean shear rates (1 – 25 s^-1) produce heterogeneous cell concentrations in the form of regions of accumulation and regions of depletion. The location of these regions relative to the flow depends on the cells’ propulsion mechanism, body shape, and flagellar arrangement, as captured by an effective aspect ratio. Species having a large effectiv...

流体流动广泛存在于自然与人工环境中，可对微生物的输运过程产生深远影响，其中涵盖水生栖息地与生物反应器内的浮游植物。然而，环境流动对浮游植物游动行为的影响迄今仍未得到充分阐释，这主要源于在微观尺度下观测细胞与流体相互作用的极大难度。本研究开展微流控实验，对四种运动型浮游植物的单个细胞进行追踪，实验中这些细胞暴露于空间非均匀流体剪切率环境——该环境特征广泛存在于自然与人工流动场景中。研究发现，中等至高平均剪切率（1~25 s⁻¹）会使细胞浓度呈现非均匀分布，具体表现为细胞富集区与耗竭区并存的格局。上述区域相对于流场的位置，取决于细胞的运动推进机制、体型结构以及鞭毛排布方式，而这些特性可通过有效长宽比进行表征。具备较大有效