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Optically trapped bacteria pairs reveal discrete motile response to control aggregation upon cell-cell approach.

Dienerowitz M, Cowan LV, Gibson GM, Hay R, Padgett MJ, Phoenix VR - Curr. Microbiol. (2014)

Bottom Line: Moreover, the motile response displays spatial sensitivity with greater cell-cell repulsion evident as inter-bacterial distances decrease.Our experiments demonstrate that repulsive forces are strongest in systems that inhibit biofilm formation (Tryptic Soy Broth), while attractive forces are weak and rare, even in systems where biofilms develop (NaCl solution).Clearly, the force-generating motility we observe during approach promotes biofilm prevention, rather than biofilm formation.

View Article: PubMed Central - PubMed

Affiliation: SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK, maria.dienerowitz@glasgow.ac.uk.

ABSTRACT
Aggregation of bacteria plays a key role in the formation of many biofilms. The critical first step is cell-cell approach, and yet the ability of bacteria to control the likelihood of aggregation during this primary phase is unknown. Here, we use optical tweezers to measure the force between isolated Bacillus subtilis cells during approach. As we move the bacteria towards each other, cell motility (bacterial swimming) initiates the generation of repulsive forces at bacterial separations of ~3 μm. Moreover, the motile response displays spatial sensitivity with greater cell-cell repulsion evident as inter-bacterial distances decrease. To examine the environmental influence on the inter-bacterial forces, we perform the experiment with bacteria suspended in Tryptic Soy Broth, NaCl solution and deionised water. Our experiments demonstrate that repulsive forces are strongest in systems that inhibit biofilm formation (Tryptic Soy Broth), while attractive forces are weak and rare, even in systems where biofilms develop (NaCl solution). These results reveal that bacteria are able to control the likelihood of aggregation during the approach phase through a discretely modulated motile response. Clearly, the force-generating motility we observe during approach promotes biofilm prevention, rather than biofilm formation.

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Environmental influence on inter-bacterial forces. The graphs display the complete datasets for the average force lines displayed in Fig. 4. Force on approach and retreat for bacteria suspended in a deionized water, b NaCl solution, c autoclaved bacteria in TSB and d 1 μm polystyrene beads. Each bold line represents the force average of six bacterial pairs or six polystyrene bead pairs. Only the interaction of bacteria in deionized water result in a repulsive force for trap separations below 3 μm. All other experiments displayed no significant change in force for decreasing the separation distance of the traps. All measurements are corrected for drift
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Fig5: Environmental influence on inter-bacterial forces. The graphs display the complete datasets for the average force lines displayed in Fig. 4. Force on approach and retreat for bacteria suspended in a deionized water, b NaCl solution, c autoclaved bacteria in TSB and d 1 μm polystyrene beads. Each bold line represents the force average of six bacterial pairs or six polystyrene bead pairs. Only the interaction of bacteria in deionized water result in a repulsive force for trap separations below 3 μm. All other experiments displayed no significant change in force for decreasing the separation distance of the traps. All measurements are corrected for drift

Mentions: The first set of experiments investigated B. subtilis cells suspended in TSB. As we decreased the separation distance d between bacteria, a majority of bacteria in the static trap began to show repulsion (they repelled themselves from their neighbour in the moving trap) at a centre-to-centre distance of approximately 3.5 µm (Fig. 3a, c). Intriguingly, as the distance between the bacteria decreased, cells commonly showed an increase in repulsive force, reaching an average maximum of 0.25 pN at a centre-to-centre separation of 2 µm (Fig. 3a, c). Then, as we moved the cells apart, the repulsive force decreased, following a similar trend to that observed during cell–cell approach (Fig. 3b, c). We repeated the experiment with cells suspended in either 0.1 M NaCl solution or deionized water (Figs. 4a, b, 5). In deionised water, again, a majority of cells displayed an increase in repulsive force as they moved closer, but the maximum average repulsive force (0.09 pN) was considerably weaker than in TSB (0.25 pN). As before, the repulsive force decreased as the optical traps moved the cells apart, closely tracking the trend observed on approach (Figs. 4b, 5a). We measured no significant repulsive force undertaking identical experiments in 0.1 M NaCl solution (Figs. 4a, b, 5b).Fig. 3


Optically trapped bacteria pairs reveal discrete motile response to control aggregation upon cell-cell approach.

Dienerowitz M, Cowan LV, Gibson GM, Hay R, Padgett MJ, Phoenix VR - Curr. Microbiol. (2014)

Environmental influence on inter-bacterial forces. The graphs display the complete datasets for the average force lines displayed in Fig. 4. Force on approach and retreat for bacteria suspended in a deionized water, b NaCl solution, c autoclaved bacteria in TSB and d 1 μm polystyrene beads. Each bold line represents the force average of six bacterial pairs or six polystyrene bead pairs. Only the interaction of bacteria in deionized water result in a repulsive force for trap separations below 3 μm. All other experiments displayed no significant change in force for decreasing the separation distance of the traps. All measurements are corrected for drift
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4201752&req=5

Fig5: Environmental influence on inter-bacterial forces. The graphs display the complete datasets for the average force lines displayed in Fig. 4. Force on approach and retreat for bacteria suspended in a deionized water, b NaCl solution, c autoclaved bacteria in TSB and d 1 μm polystyrene beads. Each bold line represents the force average of six bacterial pairs or six polystyrene bead pairs. Only the interaction of bacteria in deionized water result in a repulsive force for trap separations below 3 μm. All other experiments displayed no significant change in force for decreasing the separation distance of the traps. All measurements are corrected for drift
Mentions: The first set of experiments investigated B. subtilis cells suspended in TSB. As we decreased the separation distance d between bacteria, a majority of bacteria in the static trap began to show repulsion (they repelled themselves from their neighbour in the moving trap) at a centre-to-centre distance of approximately 3.5 µm (Fig. 3a, c). Intriguingly, as the distance between the bacteria decreased, cells commonly showed an increase in repulsive force, reaching an average maximum of 0.25 pN at a centre-to-centre separation of 2 µm (Fig. 3a, c). Then, as we moved the cells apart, the repulsive force decreased, following a similar trend to that observed during cell–cell approach (Fig. 3b, c). We repeated the experiment with cells suspended in either 0.1 M NaCl solution or deionized water (Figs. 4a, b, 5). In deionised water, again, a majority of cells displayed an increase in repulsive force as they moved closer, but the maximum average repulsive force (0.09 pN) was considerably weaker than in TSB (0.25 pN). As before, the repulsive force decreased as the optical traps moved the cells apart, closely tracking the trend observed on approach (Figs. 4b, 5a). We measured no significant repulsive force undertaking identical experiments in 0.1 M NaCl solution (Figs. 4a, b, 5b).Fig. 3

Bottom Line: Moreover, the motile response displays spatial sensitivity with greater cell-cell repulsion evident as inter-bacterial distances decrease.Our experiments demonstrate that repulsive forces are strongest in systems that inhibit biofilm formation (Tryptic Soy Broth), while attractive forces are weak and rare, even in systems where biofilms develop (NaCl solution).Clearly, the force-generating motility we observe during approach promotes biofilm prevention, rather than biofilm formation.

View Article: PubMed Central - PubMed

Affiliation: SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK, maria.dienerowitz@glasgow.ac.uk.

ABSTRACT
Aggregation of bacteria plays a key role in the formation of many biofilms. The critical first step is cell-cell approach, and yet the ability of bacteria to control the likelihood of aggregation during this primary phase is unknown. Here, we use optical tweezers to measure the force between isolated Bacillus subtilis cells during approach. As we move the bacteria towards each other, cell motility (bacterial swimming) initiates the generation of repulsive forces at bacterial separations of ~3 μm. Moreover, the motile response displays spatial sensitivity with greater cell-cell repulsion evident as inter-bacterial distances decrease. To examine the environmental influence on the inter-bacterial forces, we perform the experiment with bacteria suspended in Tryptic Soy Broth, NaCl solution and deionised water. Our experiments demonstrate that repulsive forces are strongest in systems that inhibit biofilm formation (Tryptic Soy Broth), while attractive forces are weak and rare, even in systems where biofilms develop (NaCl solution). These results reveal that bacteria are able to control the likelihood of aggregation during the approach phase through a discretely modulated motile response. Clearly, the force-generating motility we observe during approach promotes biofilm prevention, rather than biofilm formation.

Show MeSH
Related in: MedlinePlus