Institute of Bioengineering and Global Health Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK.
Nat Microbiol. 2019 May;4(5):774-780. doi: 10.1038/s41564-019-0378-9. Epub 2019 Feb 25.
Prokaryotes have the ability to walk on surfaces using type IV pili (TFP), a motility mechanism known as twitching. Molecular motors drive TFP extension and retraction, but whether and how these movements are coordinated is unknown. Here, we reveal how the pathogen Pseudomonas aeruginosa coordinates the motorized activity of TFP to power efficient surface motility. To do this, we dynamically visualized TFP extension, attachment and retraction events at high resolution in four dimensions using label-free interferometric scattering microscopy (iSCAT). By measuring TFP dynamics, we found that the retraction motor PilT was sufficient to generate tension and power motility in free solution, while its partner ATPase PilU may improve retraction only in high-friction environments. Using precise timing of successive attachment and retraction, we show that P. aeruginosa engages PilT motors very rapidly and almost only when TFP encounter the surface, suggesting contact sensing. Finally, measurements of TFP dwell times on surfaces show that tension reinforced the adhesion strength to the surface of individual pili, thereby increasing effective pulling time during retraction. The successive control of TFP extension, attachment, retraction and detachment suggests that sequential control of motility machinery is a conserved strategy for optimized locomotion across domains of life.
原核生物具有使用 IV 型菌毛（TFP）在表面上行走的能力，这是一种称为抽搐的运动机制。分子马达驱动 TFP 的延伸和缩回，但这些运动是否以及如何协调尚不清楚。在这里，我们揭示了病原体铜绿假单胞菌如何协调 TFP 的机动活动以提供有效的表面运动动力。为此，我们使用无标记干涉散射显微镜（iSCAT）在四个维度上以高分辨率动态可视化 TFP 的延伸、附着和缩回事件。通过测量 TFP 动力学，我们发现缩回马达 PilT 足以在游离溶液中产生张力并为运动提供动力，而其伴侣 ATPase PilU 可能仅在高摩擦环境中改善缩回。通过精确控制连续的附着和缩回的时间，我们表明铜绿假单胞菌非常迅速地并且几乎仅当 TFP 遇到表面时才会激活 PilT 马达，这表明存在接触感应。最后，对 TFP 在表面上的停留时间的测量表明，张力增强了单个菌毛与表面的粘附强度，从而在缩回过程中增加了有效拉动时间。TFP 的延伸、附着、缩回和脱离的连续控制表明，运动机制的顺序控制是优化跨生命领域的运动的一种保守策略。
