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Visualization of Biosurfactant Film Flow in a Bacillus subtilis Swarm Colony on an Agar Plate.

Kim K, Kim JK - Int J Mol Sci (2015)

Bottom Line: The beads were initially embedded in the agar plate and subsequently distributed spontaneously at the upper surface of the expanding colony.A distinct periodic fluctuation in the average speed and vorticity of flow in swarm colony was observed at the inner region of the colony, and correlated with the switch between bacterial swarming and growth phases.At the advancing edge of the colony, both the magnitudes of velocity and vorticity of flow in swarm colony were inversely correlated with the spreading speed of the swarm edge.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA. kkim15@ncsu.edu.

ABSTRACT
Collective bacterial dynamics plays a crucial role in colony development. Although many research groups have studied the behavior of fluidic swarm colonies, the detailed mechanics of its motion remains elusive. Here, we developed a visualization method using submicron fluorescent beads for investigating the flow field in a thin layer of fluid that covers a Bacillus subtilis swarm colony growing on an agar plate. The beads were initially embedded in the agar plate and subsequently distributed spontaneously at the upper surface of the expanding colony. We conducted long-term live cell imaging of the B. subtilis colony using the fluorescent tracers, and obtained high-resolution velocity maps of microscale vortices in the swarm colony using particle image velocimetry. A distinct periodic fluctuation in the average speed and vorticity of flow in swarm colony was observed at the inner region of the colony, and correlated with the switch between bacterial swarming and growth phases. At the advancing edge of the colony, both the magnitudes of velocity and vorticity of flow in swarm colony were inversely correlated with the spreading speed of the swarm edge. The advanced imaging tool developed in this study would facilitate further understanding of the effect of micro vortices in swarm colony on the collective dynamics of bacteria.

No MeSH data available.


Related in: MedlinePlus

Dynamics of the submicron fluorescent beads. (a) Fluorescence intensity profile of the beads in each solution at 30 s after initiation of diffusion from the 0.5% agar plate. The symbols and lines represent experimental data and regression curves obtained by Equation (1), respectively; and (b) Comparison of Deff of the bead in different solutions. Measured Deff of the beads in LB Broth (LB), supernatants of E. coli and B. subtilis were normalized by Deff in distilled water (DW). The relative magnitudes are DW > LB > E. coli > B. subtilis.
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ijms-16-20225-f001: Dynamics of the submicron fluorescent beads. (a) Fluorescence intensity profile of the beads in each solution at 30 s after initiation of diffusion from the 0.5% agar plate. The symbols and lines represent experimental data and regression curves obtained by Equation (1), respectively; and (b) Comparison of Deff of the bead in different solutions. Measured Deff of the beads in LB Broth (LB), supernatants of E. coli and B. subtilis were normalized by Deff in distilled water (DW). The relative magnitudes are DW > LB > E. coli > B. subtilis.

Mentions: Escaping of the fluorescent beads embedded in the top layer of the agar plate was caused by diffusion across the concentration gradient between the solution and the agar gel. Both the fluorescence intensity profile of the bead distribution in each solution and the regression curve produced by the Equation (1) at 30 s after initiation of diffusion are plotted in Figure 1a. The regression curves are well matched with the variation trends of measured data. We estimated an effective diffusion coefficient (Deff) of the bead by the regression analysis and compared Deff in different solutions such as distilled water, Luria-Bertani (LB) broth, and supernatants of E. coli and B. subtilis. Deff was highest in the distilled water and the magnitude was decreased in the order of LB Broth, E. coli, and B. subtilis as shown in Figure 1b. We demonstrated that the movement of the fluorescent beads from the agar gel was induced by diffusion mechanism. In the regression analysis, the coefficient of determination (R2) was higher than 0.95 and the average residual was lower than 0.05. When the surface of the agar plate was more dried, more beads were escaped from the agar gel. This result is consistent with a previous finding that the spatial gradient of the biosurfactant concentration leads to marangoni effect [10], and provides a clue to our observation that the fluorescent beads in the B. subtilis colony secreting biosurfactant get away from the agar plate, and the beads in the E. coli colony secreting wetting agent are immobilized at the upper surface of the colony [11].


Visualization of Biosurfactant Film Flow in a Bacillus subtilis Swarm Colony on an Agar Plate.

Kim K, Kim JK - Int J Mol Sci (2015)

Dynamics of the submicron fluorescent beads. (a) Fluorescence intensity profile of the beads in each solution at 30 s after initiation of diffusion from the 0.5% agar plate. The symbols and lines represent experimental data and regression curves obtained by Equation (1), respectively; and (b) Comparison of Deff of the bead in different solutions. Measured Deff of the beads in LB Broth (LB), supernatants of E. coli and B. subtilis were normalized by Deff in distilled water (DW). The relative magnitudes are DW > LB > E. coli > B. subtilis.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4613199&req=5

ijms-16-20225-f001: Dynamics of the submicron fluorescent beads. (a) Fluorescence intensity profile of the beads in each solution at 30 s after initiation of diffusion from the 0.5% agar plate. The symbols and lines represent experimental data and regression curves obtained by Equation (1), respectively; and (b) Comparison of Deff of the bead in different solutions. Measured Deff of the beads in LB Broth (LB), supernatants of E. coli and B. subtilis were normalized by Deff in distilled water (DW). The relative magnitudes are DW > LB > E. coli > B. subtilis.
Mentions: Escaping of the fluorescent beads embedded in the top layer of the agar plate was caused by diffusion across the concentration gradient between the solution and the agar gel. Both the fluorescence intensity profile of the bead distribution in each solution and the regression curve produced by the Equation (1) at 30 s after initiation of diffusion are plotted in Figure 1a. The regression curves are well matched with the variation trends of measured data. We estimated an effective diffusion coefficient (Deff) of the bead by the regression analysis and compared Deff in different solutions such as distilled water, Luria-Bertani (LB) broth, and supernatants of E. coli and B. subtilis. Deff was highest in the distilled water and the magnitude was decreased in the order of LB Broth, E. coli, and B. subtilis as shown in Figure 1b. We demonstrated that the movement of the fluorescent beads from the agar gel was induced by diffusion mechanism. In the regression analysis, the coefficient of determination (R2) was higher than 0.95 and the average residual was lower than 0.05. When the surface of the agar plate was more dried, more beads were escaped from the agar gel. This result is consistent with a previous finding that the spatial gradient of the biosurfactant concentration leads to marangoni effect [10], and provides a clue to our observation that the fluorescent beads in the B. subtilis colony secreting biosurfactant get away from the agar plate, and the beads in the E. coli colony secreting wetting agent are immobilized at the upper surface of the colony [11].

Bottom Line: The beads were initially embedded in the agar plate and subsequently distributed spontaneously at the upper surface of the expanding colony.A distinct periodic fluctuation in the average speed and vorticity of flow in swarm colony was observed at the inner region of the colony, and correlated with the switch between bacterial swarming and growth phases.At the advancing edge of the colony, both the magnitudes of velocity and vorticity of flow in swarm colony were inversely correlated with the spreading speed of the swarm edge.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA. kkim15@ncsu.edu.

ABSTRACT
Collective bacterial dynamics plays a crucial role in colony development. Although many research groups have studied the behavior of fluidic swarm colonies, the detailed mechanics of its motion remains elusive. Here, we developed a visualization method using submicron fluorescent beads for investigating the flow field in a thin layer of fluid that covers a Bacillus subtilis swarm colony growing on an agar plate. The beads were initially embedded in the agar plate and subsequently distributed spontaneously at the upper surface of the expanding colony. We conducted long-term live cell imaging of the B. subtilis colony using the fluorescent tracers, and obtained high-resolution velocity maps of microscale vortices in the swarm colony using particle image velocimetry. A distinct periodic fluctuation in the average speed and vorticity of flow in swarm colony was observed at the inner region of the colony, and correlated with the switch between bacterial swarming and growth phases. At the advancing edge of the colony, both the magnitudes of velocity and vorticity of flow in swarm colony were inversely correlated with the spreading speed of the swarm edge. The advanced imaging tool developed in this study would facilitate further understanding of the effect of micro vortices in swarm colony on the collective dynamics of bacteria.

No MeSH data available.


Related in: MedlinePlus