Prokaryotes have the ability to walk on surfaces using type IV pili (TFP), a motility mechanism known as twitching1,2. Molecular motors drive TFP extension and retraction, but whether and how these movements are coordinated is unknown3. 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)4. 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.

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The authors would like to thank J. Andrecka for valuable discussions on iSCAT, J. Engel and Y. Inclan for strains and plasmids and Z. Al-Mayyah for help with generating one mutant strain. L.T. and A.P. thank the Swiss National Foundation for funding this work through Projects (grant No. 31003A_169377) and the Gabriella Giorgi-Cavaglieri Foundation.

Author information


  1. Institute of Bioengineering and Global Health Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

    • Lorenzo Talà
    •  & Alexandre Persat
  2. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, UK

    • Adam Fineberg
    •  & Philipp Kukura


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L.T. and A.P conceptualized the study and performed experiments and data analysis. L.T., A.F. and P.K. implemented and adapted the iSCAT microscope for live-cell imaging. L.T., P.K and A.P. wrote the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Alexandre Persat.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–7 and Supplementary Video Legends.

  2. Reporting Summary

  3. Supplementary Video 1

    iSCAT visualization of a twitching WT cell.

  4. Supplementary Video 2

    iSCAT visualization of a twitching fliC cell.

  5. Supplementary Video 3

    iSCAT visualization of the fliC mutant.

  6. Supplementary Video 4

    iSCAT visualization of the pilTU fliC mutant.

  7. Supplementary Video 5

    iSCAT visualization of the retraction motor mutant pilT fliC.

  8. Supplementary Video 6

    iSCAT visualization of the retraction motor mutant pilU fliC.

  9. Supplementary Video 7

    iSCAT visualization of a twitching pilU fliC cell.

  10. Supplementary Video 8

    Visualization of twitching motility in high friction environment highlights a function for PilU in force generation.

  11. Supplementary Video 9

    iSCAT visualization of extension, attachment and retraction of a TFP.

  12. Supplementary Video 10

    iSCAT visualization of extension, attachment and retraction of a TFP.

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