铜绿假单胞菌在液滴界面的二维和三维运动特征

Two-dimensional and three-dimensional motion of Pseudomonas aeruginosa at the droplet interface

摘要:

【目的】环境中无处不在的气-液界面能够影响细菌的运动和养分的传输扩散，进而调控微生物的种群互作和群落结构。因此，系统地认知微生物在微观界面的运动特征对于理解和解析微生物多样性的产生、维持机制以及生态功能至关重要。【方法】本文基于微流体显微系统(超高速荧光显微镜和数字全息显微镜)，以具备主动运动能力的模式菌株铜绿假单胞菌(Pseudomonas aeruginosa PAO1)为研究对象，观测并解析了细菌细胞在气-液界面的二维运动特征和气-液-固界面的二维与三维运动特征。【结果】PAO1既能在气-液界面处执行近似直线轨迹的运动，也能在气-液界面下方执行顺时针或逆时针旋转的圆周运动(最小曲率半径R_min=3µm)。在气-液-固界面处，6.45%的不运动细胞聚集于气-液-固界面边缘处，并在该处完成不可逆附着；同时，游动细胞由于受到液滴内部毛细管流和马兰戈尼(Marangoni)涡流运动的综合作用，直线游动至距界面约40 μm内的区域后，其运动轨迹转变为垂直界面方向返回或以近似界面平行方向运动并附着，这些行为显著调节了PAO1的空间分布，促使了其朝向气-液-固界面的迁移，表明个体PAO1的鞭毛在此处的主动游动作用较弱。【结论】PAO1在气-液界面处能够执行与固-液界面类似的运动轨迹，且能够在各种作用力下朝向气-液-固界面运动并附着。

Abstract:

[Objective] The ubiquitous air-liquid interfaces affect bacterial motility and nutrient transport, thereby regulating the interaction among microbial populations and microbial community structure. Therefore, it is of vital importance for understanding and elucidating the mechanisms of microbial diversity generation and maintenance as well as the ecological functions to clarify the movement characteristics of microorganisms at microscopic interfaces. [Methods] With microfluidic microscopes (ultra-high speed fluorescence microscope and digital holographic microscope), we quantified the movement patterns of Pseudomonas aeruginosa (PAO1) cells near air-liquid-solid and air-liquid interfaces of droplet. [Results] Below the air-liquid interfaces, the trajectories of PAO1 are as follows:straight lines, clockwise circles, or counterclockwise circles with R_min(minimum radius of curvature)=3 µm. At the air-liquid-solid interfaces, 6.45% of the immobile cells accumulated at the edge of the interfaces and completed irreversible attachment directly. Meanwhile, due to capillary flow and Marangoni effect inside the droplet, mobile cells returned in the direction perpendicular to the interface or moved in the direction approximately parallel to the interface and attached after swimming in a straight line to a region within about 40 µm from the interface. These behaviors significantly modulated the spatial distribution of PAO1, promoting the migration toward the air-liquid-solid interface. Therefore, the active flagellar motility played a little role in the process. [Conclusion] With similar trajectories in both the solid-liquid interfaces and the air-liquid interfaces, PAO1 can move towards and subsequently attach onto the air-liquid-solid interfaces under the complex cell-surface interfacial forces.