Chengala Anwar, Hondzo Miki, Sheng Jian
St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 May;87(5):052704. doi: 10.1103/PhysRevE.87.052704. Epub 2013 May 9.
Using high-speed digital holographic microscopy and microfluidics, we discover that, when encountering fluid flow shear above a threshold, unicellular green alga Dunaliella primolecta migrates unambiguously in the cross-stream direction that is normal to the plane of shear and coincides with the local fluid flow vorticity. The flow shear drives motile microalgae to collectively migrate in a thin two-dimensional horizontal plane and consequently alters the spatial distribution of microalgal cells within a given suspension. This shear-induced algal migration differs substantially from periodic rotational motion of passive ellipsoids, known as Jeffery orbits, as well as gyrotaxis by bottom-heavy swimming microalgae in a shear flow due to the subtle interplay between torques generated by gravity and viscous shear. Our findings could facilitate mechanistic solutions for modeling planktonic thin layers and sustainable cultivation of microalgae for human nutrition and bioenergy feedstock.
利用高速数字全息显微镜和微流控技术，我们发现，当遇到高于阈值的流体流动剪切力时，单细胞绿藻杜氏盐藻会明确地在与剪切平面垂直且与局部流体流动涡度一致的横向方向上迁移。流动剪切力驱动运动性微藻在薄的二维水平平面上集体迁移，从而改变给定悬浮液中微藻细胞的空间分布。这种剪切诱导的藻类迁移与被动椭球体的周期性旋转运动（即杰弗里轨道）以及底部较重的游动微藻在剪切流中的回转趋性有很大不同，这是由于重力和粘性剪切产生的扭矩之间的微妙相互作用。我们的发现有助于为浮游薄层建模以及为人类营养和生物能源原料进行微藻可持续培养提供机制解决方案。
