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Psl trails guide exploration and microcolony formation in Pseudomonas aeruginosa biofilms.

Zhao K, Tseng BS, Beckerman B, Jin F, Gibiansky ML, Harrison JJ, Luijten E, Parsek MR, Wong GC - Nature (2013)

Bottom Line: Bacterial biofilms are surface-associated, multicellular, morphologically complex microbial communities.This Pareto-type behaviour indicates that the bacterial community self-organizes in a manner analogous to a capitalist economic system, 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of California, Los Angeles, California 90095, USA.

ABSTRACT
Bacterial biofilms are surface-associated, multicellular, morphologically complex microbial communities. Biofilm-forming bacteria such as the opportunistic pathogen Pseudomonas aeruginosa are phenotypically distinct from their free-swimming, planktonic counterparts. 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'. 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 surface. 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-type behaviour indicates that the bacterial community self-organizes in a manner analogous to a capitalist economic system, 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.

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Efficiency of surface coverage by bacterial trajectories and correlation with Psl trails a–d. Cumulative surface coverage at 0.5 (a, b) and 5 hours (c, d). Top row is for WT and bottom row for ΔpslD. Red and black colors indicate used (i.e. covered by bacterial trajectories) and fresh surface, respectively. Bacteria in the current frame are shown in green. e. Reconstructed bacterial trajectories of WT generated between 16.3 and 18.7 hours after inoculation (color bar indicates the time a given cell spent at each point). f. Psl trail left behind by bacteria in the same period, stained by fluorescently conjugated HHA lectin. Scale bars are 10 μm.
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Figure 1: Efficiency of surface coverage by bacterial trajectories and correlation with Psl trails a–d. Cumulative surface coverage at 0.5 (a, b) and 5 hours (c, d). Top row is for WT and bottom row for ΔpslD. Red and black colors indicate used (i.e. covered by bacterial trajectories) and fresh surface, respectively. Bacteria in the current frame are shown in green. e. Reconstructed bacterial trajectories of WT generated between 16.3 and 18.7 hours after inoculation (color bar indicates the time a given cell spent at each point). f. Psl trail left behind by bacteria in the same period, stained by fluorescently conjugated HHA lectin. Scale bars are 10 μm.

Mentions: Consistent with the role of Psl in surface adhesion7,24, the average surface residence time of a PAO1 ΔpslD mutant strain (which cannot produce Psl) was 35 ± 10% shorter than that of WT. Tracking algorithms allow us to isolate differences in spatial characteristics of cell–surface interactions, in addition to temporal characteristics such as residence time. We observed a fundamental difference in surface exploration patterns between these strains (Figure 1a-d, Supplementary Video 1) when we tracked the motility history of all cells in a 67 × 67 µm2 field of view (>700,000 images of individual cells, 11 hours of data, 3 second/frame time resolution). In Figures 1a–d, black regions represent ‘untouched’ surface areas, while red regions represent areas visited by bacteria. For WT, the surface coverage increased slowly to a maximum of ~55 ± 5% in 5 hours. In contrast, the ΔpslD mutant covered 79 ± 10% in 5 hours. These observed differences are not due to differences in growth between strains (Supplementary Figure 1). To confirm that changes in surface motility rather than changes in the numbers of bacteria visiting the surface are responsible for these observations, we also compared WT and ΔpslD at the same total number of bacterial visits (i.e. the sum of the number of bacteria in all frames Ns = Σni, where ni is the number of bacteria in frame i; Supplementary Figure 2). Indeed, essentially the same trend was observed, with a surface coverage of 52 ± 4% for WT at Ns =124,000 and a surface coverage of 83 ± 10% for ΔpslD at the same Ns. These are averages from at least three replicates (see Supplementary Methods).


Psl trails guide exploration and microcolony formation in Pseudomonas aeruginosa biofilms.

Zhao K, Tseng BS, Beckerman B, Jin F, Gibiansky ML, Harrison JJ, Luijten E, Parsek MR, Wong GC - Nature (2013)

Efficiency of surface coverage by bacterial trajectories and correlation with Psl trails a–d. Cumulative surface coverage at 0.5 (a, b) and 5 hours (c, d). Top row is for WT and bottom row for ΔpslD. Red and black colors indicate used (i.e. covered by bacterial trajectories) and fresh surface, respectively. Bacteria in the current frame are shown in green. e. Reconstructed bacterial trajectories of WT generated between 16.3 and 18.7 hours after inoculation (color bar indicates the time a given cell spent at each point). f. Psl trail left behind by bacteria in the same period, stained by fluorescently conjugated HHA lectin. Scale bars are 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4109411&req=5

Figure 1: Efficiency of surface coverage by bacterial trajectories and correlation with Psl trails a–d. Cumulative surface coverage at 0.5 (a, b) and 5 hours (c, d). Top row is for WT and bottom row for ΔpslD. Red and black colors indicate used (i.e. covered by bacterial trajectories) and fresh surface, respectively. Bacteria in the current frame are shown in green. e. Reconstructed bacterial trajectories of WT generated between 16.3 and 18.7 hours after inoculation (color bar indicates the time a given cell spent at each point). f. Psl trail left behind by bacteria in the same period, stained by fluorescently conjugated HHA lectin. Scale bars are 10 μm.
Mentions: Consistent with the role of Psl in surface adhesion7,24, the average surface residence time of a PAO1 ΔpslD mutant strain (which cannot produce Psl) was 35 ± 10% shorter than that of WT. Tracking algorithms allow us to isolate differences in spatial characteristics of cell–surface interactions, in addition to temporal characteristics such as residence time. We observed a fundamental difference in surface exploration patterns between these strains (Figure 1a-d, Supplementary Video 1) when we tracked the motility history of all cells in a 67 × 67 µm2 field of view (>700,000 images of individual cells, 11 hours of data, 3 second/frame time resolution). In Figures 1a–d, black regions represent ‘untouched’ surface areas, while red regions represent areas visited by bacteria. For WT, the surface coverage increased slowly to a maximum of ~55 ± 5% in 5 hours. In contrast, the ΔpslD mutant covered 79 ± 10% in 5 hours. These observed differences are not due to differences in growth between strains (Supplementary Figure 1). To confirm that changes in surface motility rather than changes in the numbers of bacteria visiting the surface are responsible for these observations, we also compared WT and ΔpslD at the same total number of bacterial visits (i.e. the sum of the number of bacteria in all frames Ns = Σni, where ni is the number of bacteria in frame i; Supplementary Figure 2). Indeed, essentially the same trend was observed, with a surface coverage of 52 ± 4% for WT at Ns =124,000 and a surface coverage of 83 ± 10% for ΔpslD at the same Ns. These are averages from at least three replicates (see Supplementary Methods).

Bottom Line: Bacterial biofilms are surface-associated, multicellular, morphologically complex microbial communities.This Pareto-type behaviour indicates that the bacterial community self-organizes in a manner analogous to a capitalist economic system, 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of California, Los Angeles, California 90095, USA.

ABSTRACT
Bacterial biofilms are surface-associated, multicellular, morphologically complex microbial communities. Biofilm-forming bacteria such as the opportunistic pathogen Pseudomonas aeruginosa are phenotypically distinct from their free-swimming, planktonic counterparts. 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'. 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 surface. 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-type behaviour indicates that the bacterial community self-organizes in a manner analogous to a capitalist economic system, 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.

Show MeSH
Related in: MedlinePlus