Psl trails guide exploration and microcolony formation in Pseudomonas aeruginosa biofilms



Bacterial biofilms are surface-associated, multicellular, morphologically complex microbial communities1,2,3,4,5,6,7. Biofilm-forming bacteria such as the opportunistic pathogen Pseudomonas aeruginosa are phenotypically distinct from their free-swimming, planktonic counterparts7,8,9,10. Much work has focused on factors affecting surface adhesion, and it is known that P. aeruginosa secretes the Psl exopolysaccharide, which promotes surface attachment by acting as ‘molecular glue’11,12,13,14,15. However, how individual surface-attached bacteria self-organize into microcolonies, the first step in communal biofilm organization, is not well understood. Here we identify a new role for Psl in early biofilm development using a massively parallel cell-tracking algorithm to extract the motility history of every cell on a newly colonized surface16. By combining this technique with fluorescent Psl staining and computer simulations, we show that P. aeruginosa deposits a trail of Psl as it moves on a surface, which influences the surface motility of subsequent cells that encounter these trails and thus generates positive feedback. Both experiments and simulations indicate that the web of secreted Psl controls the distribution of surface visit frequencies, which can be approximated by a power law. This Pareto-type17 behaviour indicates that the bacterial community self-organizes in a manner analogous to a capitalist economic system18, a ‘rich-get-richer’ mechanism of Psl accumulation that results in a small number of ‘elite’ cells becoming extremely enriched in communally produced Psl. Using engineered strains with inducible Psl production, we show that local Psl concentrations determine post-division cell fates and that high local Psl concentrations ultimately allow elite cells to serve as the founding population for initial microcolony development.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Efficiency of surface coverage by bacterial trajectories and correlation with Psl trails.
Figure 2: Visit frequency distribution and its effect on bacterial movement.
Figure 3: Local Psl levels determine post-division cell fates.


  1. 1

    Costerton, J. W., Stewart, P. S. & Greenberg, E. P. Bacterial biofilms: a common cause of persistent infections. Science 284, 1318–1322 (1999)

  2. 2

    O’Toole, G. A. & Kolter, R. Flagellar and twitching motility are necessary for Pseudomonas aeruginosa biofilm development. Mol. Microbiol. 30, 295–304 (1998)

  3. 3

    O’Toole, G., Kaplan, H. B. & Kolter, R. Biofilm formation as microbial development. Annu. Rev. Microbiol. 54, 49–79 (2000)

  4. 4

    Stoodley, P., Sauer, K., Davies, D. G. & Costerton, J. W. Biofilms as complex differentiated communities. Annu. Rev. Microbiol. 56, 187–209 (2002)

  5. 5

    Klausen, M., Aaes-Jørgensen, A., Molin, S. & Tolker-Nielsen, T. Involvement of bacterial migration in the development of complex multicellular structures in Pseudomonas aeruginosa biofilms. Mol. Microbiol. 50, 61–68 (2003)

  6. 6

    Davies, D. G. et al. The involvement of cell-to-cell signals in the development of a bacterial biofilm. Science 280, 295–298 (1998)

  7. 7

    Mann, E. E. & Wozniak, D. J. Pseudomonas biofilm matrix composition and niche biology. FEMS Microbiol. Rev. 36, 893–916 (2012)

  8. 8

    Lyczak, J. B., Cannon, C. L. & Pier, G. B. Establishment of Pseudomonas aeruginosa infection: lessons from a versatile opportunist. Microbes Infect. 2, 1051–1060 (2000)

  9. 9

    Tatterson, L. E., Poschet, J. F., Firoved, A., Skidmore, J. & Deretic, V. CFTR and pseudomonas infections in cystic fibrosis. Front. Biosci. 6, d890–897 (2001)

  10. 10

    Singh, P. K. et al. Quorum-sensing signals indicate that cystic fibrosis lungs are infected with bacterial biofilms. Nature 407, 762–764 (2000)

  11. 11

    Friedman, L. & Kolter, R. Two genetic loci produce distinct carbohydrate-rich structural components of the Pseudomonas aeruginosa biofilm matrix. J. Bacteriol. 186, 4457–4465 (2004)

  12. 12

    Ma, L. Y., Lu, H. P., Sprinkle, A., Parsek, M. R. & Wozniak, D. J. Pseudomonas aeruginosa Psl is a galactose- and mannose-rich exopolysaccharide. J. Bacteriol. 189, 8353–8356 (2007)

  13. 13

    Byrd, M. S. et al. Genetic and biochemical analyses of the Pseudomonas aeruginosa Psl exopolysaccharide reveal overlapping roles for polysaccharide synthesis enzymes in Psl and LPS production. Mol. Microbiol. 73, 622–638 (2009)

  14. 14

    Ma, L., Jackson, K. D., Landry, R. M., Parsek, M. R. & Wozniak, D. J. Analysis of Pseudomonas aeruginosa conditional psl variants reveals roles for the psl polysaccharide in adhesion and maintaining biofilm structure postattachment. J. Bacteriol. 188, 8213–8221 (2006)

  15. 15

    Byrd, M. S., Pang, B., Mishra, M., Swords, W. E. & Wozniak, D. J. The Pseudomonas aeruginosa exopolysaccharide Psl facilitates surface adherence and NF-κB activation in A549 cells. mBio 1, e00140–10 (2010)

  16. 16

    Gibiansky, M. L. et al. Bacteria use type IV pili to walk upright and detach from surfaces. Science 330, 197 (2010)

  17. 17

    Newman, M. E. J. Power laws, Pareto distributions and Zipf’s law. Contemp. Phys. 46, 323–351 (2005)

  18. 18

    Gabaix, X. Power laws in economics and finance. Annu. Rev. Econ. 1, 255–294 (2009)

  19. 19

    Eagon, R. G. Composition of an extracellular slime produced by Pseudomonas aeruginosa. Can. J. Microbiol. 8, 585–586 (1962)

  20. 20

    Sutherland, I. W. The biofilm matrix: an immobilized but dynamic microbial environment. Trends Microbiol. 9, 222–227 (2001)

  21. 21

    Whitchurch, C. B., Tolker-Nielsen, T., Ragas, P. C. & Mattick, J. S. Extracellular DNA required for bacterial biofilm formation. Science 295, 1487 (2002)

  22. 22

    Colvin, K. M. et al. The Pel and Psl polysaccharides provide Pseudomonas aeruginosa structural redundancy within the biofilm matrix. Environ. Microbiol. 14, 1913–1928 (2012)

  23. 23

    Monroe, D. Looking for chinks in the armor of bacterial biofilms. PLoS Biol. 5, e307 (2007)

  24. 24

    Flemming, H. C., Neu, T. R. & Wozniak, D. J. The EPS matrix: the “house of biofilm cells”. J. Bacteriol. 189, 7945–7947 (2007)

  25. 25

    Newman, J. R. & Fuqua, C. Broad-host-range expression vectors that carry the l-arabinose-inducible Escherichia coli araBAD promoter and the araC regulator. Gene 227, 197–203 (1999)

  26. 26

    Skerker, J. M. & Berg, H. C. Direct observation of extension and retraction of type IV pili. Proc. Natl Acad. Sci. USA 98, 6901–6904 (2001)

  27. 27

    Solomon, S. & Richmond, P. Power laws of wealth, market order volumes and market returns. Physica A 299, 188–197 (2001)

  28. 28

    Holloway, B. W. Genetic recombination in Pseudomonas aeruginosa. J. Gen. Microbiol. 13, 572–581 (1955)

  29. 29

    Heydorn, A. et al. Experimental reproducibility in flow-chamber biofilms. Microbiology 146, 2409–2415 (2000)

  30. 30

    Sternberg, C. & Tolker-Nielsen, T. Growing and analyzing biofilms in flow cells. Curr. Protocols Microbiol. 21, 1B.2.1–1B.2.17 (2006)

  31. 31

    Lecuyer, S. et al. Shear stress increases the residence time of adhesion of Pseudomonas aeruginosa. Biophys. J. 100, 341–350 (2011)

  32. 32

    Ma, L. et al. Assembly and development of the Pseudomonas aeruginosa biofilm matrix. PLoS Pathog. 5, e1000354 (2009)

Download references


K.Z., B.S.T., M.R.P. and G.C.L.W. are supported by the US National Institutes of Health (NIH 1RO1HL087920). K.Z. and G.C.L.W. also acknowledge support from the US National Science Foundation (NSF DMR1106106) and a UCLA Transdisciplinary Seed Grant. B.S.T., J.J.H. and M.R.P. also acknowledge support from the NIH (R01AI077628, R01AI081983, R56AI061396) and NSF (MCB0822405). B.S.T. is supported by the Cystic Fibrosis Foundation Postdoctoral Fellowship (TSENG11F0). J.J.H. was supported by a postdoctoral fellowship from the Natural Sciences and Engineering Research Council of Canada. B.B. and E.L. acknowledge support from the NSF under DMR-1006430 (E.L.) and DGE-0824162 (B.B.). The authors would like to thank J. Copic for discussions and R. J. Siehnel for technical assistance. We dedicate this paper to the memory of M. Shannon.

Author information




G.C.L.W., M.R.P. and K.Z. conceived the project. K.Z., B.S.T., M.R.P. and G.C.L.W. designed studies. K.Z. and B.S.T. performed experimental measurements. K.Z. and G.C.L.W. performed image analysis. F.J. helped in performing image analysis. M.L.G. helped in collecting experimental data. B.S.T., J.J.H. and M.R.P. constructed strains. B.B. and E.L. designed the model and performed computer simulations. K.Z., B.S.T., B.B., E.L., M.R.P. and G.C.L.W. wrote the paper. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Erik Luijten or Matthew R. Parsek or Gerard C. L. Wong.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1-16, Supplementary Methods, Supplementary Tables 1-3 and Supplementary References. (PDF 1308 kb)

The left panels show the bright field videos while the right panels show the corresponding evolution of surface coverage by bacterial trajectories (WT (top row) and ΔpslD (bottom row)). In the right panels, red and black regions indicate used and fresh surfaces, respectively. For clarity, cells that reside on fresh surfaces are colored yellow, whereas cells that reside on used surfaces are colored purple. (MOV 30225 kb)

Evolution of surface coverage by bacterial trajectories

The left panels show the bright field videos while the right panels show the corresponding evolution of surface coverage by bacterial trajectories (WT (top row) and ΔpslD (bottom row)). In the right panels, red and black regions indicate used and fresh surfaces, respectively. For clarity, cells that reside on fresh surfaces are colored yellow, whereas cells that reside on used surfaces are colored purple. (MOV 30225 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Zhao, K., Tseng, B., Beckerman, B. et al. Psl trails guide exploration and microcolony formation in Pseudomonas aeruginosa biofilms. Nature 497, 388–391 (2013).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.