Ping Liyan, Wasnik Vaibhav, Emberly Eldon
Max Planck Institute for Chemical Ecology, Hans-Knoell-Str. 8, D-07745 Jena, Germany Current address: Rowland Institute at Harvard University, 100 Edwin H. Land Blvd, Cambridge, MA 02142, USA
Physics Department, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada.
FEMS Microbiol Ecol. 2015 Feb;91(2):1-7. doi: 10.1093/femsec/fiu020. Epub 2014 Dec 8.
Motile bacteria often have to pass through small tortuous pores in soil or tissue of higher organisms. However, their motion in this prevalent type of niche is not fully understood. Here, we modeled it with narrow glass capillaries and identified a critical radius (Rc) for bacterial motion. Near the surface of capillaries narrower than that, the swimming trajectories are helices. In larger capillaries, they swim in distorted circles. Under non-slip condition, the peritrichous Escherichia coli swam in left-handed helices with an Rc of ~10 μm near glass surface. However, slipping could occur in the fast monotrichous Pseudomonas fluorescens, when a speed threshold was exceeded, and thus both left-handed and right-handed helices were executed in glass capillaries. In the natural non-cylindrical pores, the near-surface trajectories would be spirals and twisted loops. Engaging in such motions reduces the bacterial migration rate. With a given pore size, the run length and the tumbling angle of the bacterium determine the probability and duration of their near-surface motion. Shear flow and chemotaxis potentially enhance it. Based on this observation, the puzzling previous observations on bacterial migration in porous environments can be interpreted.
游动细菌常常需要穿过高等生物土壤或组织中狭窄而曲折的孔隙。然而，它们在这种普遍存在的生态位中的运动尚未完全被理解。在这里，我们用狭窄的玻璃毛细管对其进行建模，并确定了细菌运动的临界半径（Rc）。在比该半径窄的毛细管表面附近，游动轨迹为螺旋线。在较大的毛细管中，它们以扭曲的圆圈游动。在无滑移条件下，周生鞭毛的大肠杆菌在玻璃表面附近以左旋螺旋线游动，Rc约为10μm。然而，当超过速度阈值时，快速单生鞭毛的荧光假单胞菌可能会发生滑移，因此在玻璃毛细管中会出现左旋和右旋螺旋线。在天然的非圆柱形孔隙中，近表面轨迹将是螺旋线和扭曲的环。进行这样的运动会降低细菌的迁移速率。对于给定的孔径，细菌的游动长度和翻滚角度决定了它们近表面运动的概率和持续时间。剪切流和趋化作用可能会增强这种运动。基于这一观察结果，可以解释之前在多孔环境中关于细菌迁移的令人困惑的观察结果。
