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Social interactions in myxobacterial swarming.

Wu Y, Jiang Y, Kaiser D, Alber M - PLoS Comput. Biol. (2007)

Bottom Line: Also, the model is able to quantify the contributions of S motility and A motility to swarming.Some pathogenic bacteria spread over infected tissue by swarming.The model described here may shed some light on their colonization process.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Notre Dame, Notre Dame, Indiana, United States of America.

ABSTRACT
Swarming, a collective motion of many thousands of cells, produces colonies that rapidly spread over surfaces. In this paper, we introduce a cell-based model to study how interactions between neighboring cells facilitate swarming. We chose to study Myxococcus xanthus, a species of myxobacteria, because it swarms rapidly and has well-defined cell-cell interactions mediated by type IV pili and by slime trails. The aim of this paper is to test whether the cell contact interactions, which are inherent in pili-based S motility and slime-based A motility, are sufficient to explain the observed expansion of wild-type swarms. The simulations yield a constant rate of swarm expansion, which has been observed experimentally. Also, the model is able to quantify the contributions of S motility and A motility to swarming. Some pathogenic bacteria spread over infected tissue by swarming. The model described here may shed some light on their colonization process.

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Diagram Showing the Two Types of Social Interactions for a Cell (Black)Although the pilus length varies with extension, retraction, and breakage, most pili are on the order of one cell length [39]. Area I represents the pilus–cell interaction area. Its sides are taken as the average pilus length. If either the head or the tail of another cell falls within this area, it can be contacted by pili from the black cell. Area II is the corresponding interaction area for A motility. A bent gray cell in direct contact with a dark cell illustrates the bending and alignment due to collisions between cells. Slime trail following is illustrated by trails (light gray shaded area) inside of area II. An artificially low cell density has been used in this figure to clarify the several interactions. In reality, many cells are adjacent to each other within the interaction area.
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pcbi-0030253-g004: Diagram Showing the Two Types of Social Interactions for a Cell (Black)Although the pilus length varies with extension, retraction, and breakage, most pili are on the order of one cell length [39]. Area I represents the pilus–cell interaction area. Its sides are taken as the average pilus length. If either the head or the tail of another cell falls within this area, it can be contacted by pili from the black cell. Area II is the corresponding interaction area for A motility. A bent gray cell in direct contact with a dark cell illustrates the bending and alignment due to collisions between cells. Slime trail following is illustrated by trails (light gray shaded area) inside of area II. An artificially low cell density has been used in this figure to clarify the several interactions. In reality, many cells are adjacent to each other within the interaction area.

Mentions: Pilus-mediated interactions depend on the dynamics of pilus retraction [23] and on the spatial distribution of the fibrils to which the pilus tips have attached [24,25]. Although these factors are mechanically complex and not yet understood in detail, the interaction has straightforward effects. Pilus retraction provides a driving force for cell movement that happens to be large, several times larger than the force developed by muscle acto-myosin. And, because the force is almost never directed along the cell's long axis, the force tends to reorient the direction of gliding. Because we are confined by the approximation that isolated cells move with constant speed, we need only consider the reorienting effect of pilus retraction. No effect on cell speed is considered, except that it drops to zero when one cell collides with another. Inasmuch as the fibrils tend to bundle groups of cells, as will be described below, the large size of the cell cluster prevents a significant reorientation of the bundle; only the cell whose pili have attached is reoriented. We model the reorientation effect of pilus-mediated interactions as driving the local alignment of cells (see area I of Figure 4 and Methods). Although we represent the interaction area by a rectangle, a circle or some irregular domain could have been used. The important quality of an interaction domain is its area. That area is proportional to the probability that a cell has an interaction. Swarms of wild-type cells cover a larger area than those of A+S− or A−S+ mutants [11]. Moreover, the peninsulas are denser with cells that are well-aligned side by side [10]. Both effects illustrate reorientation due to pilus retraction. Cell clusters tend to be narrow in the case of an A+S− mutant and wide in the case of wild-type bacteria.


Social interactions in myxobacterial swarming.

Wu Y, Jiang Y, Kaiser D, Alber M - PLoS Comput. Biol. (2007)

Diagram Showing the Two Types of Social Interactions for a Cell (Black)Although the pilus length varies with extension, retraction, and breakage, most pili are on the order of one cell length [39]. Area I represents the pilus–cell interaction area. Its sides are taken as the average pilus length. If either the head or the tail of another cell falls within this area, it can be contacted by pili from the black cell. Area II is the corresponding interaction area for A motility. A bent gray cell in direct contact with a dark cell illustrates the bending and alignment due to collisions between cells. Slime trail following is illustrated by trails (light gray shaded area) inside of area II. An artificially low cell density has been used in this figure to clarify the several interactions. In reality, many cells are adjacent to each other within the interaction area.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2230681&req=5

pcbi-0030253-g004: Diagram Showing the Two Types of Social Interactions for a Cell (Black)Although the pilus length varies with extension, retraction, and breakage, most pili are on the order of one cell length [39]. Area I represents the pilus–cell interaction area. Its sides are taken as the average pilus length. If either the head or the tail of another cell falls within this area, it can be contacted by pili from the black cell. Area II is the corresponding interaction area for A motility. A bent gray cell in direct contact with a dark cell illustrates the bending and alignment due to collisions between cells. Slime trail following is illustrated by trails (light gray shaded area) inside of area II. An artificially low cell density has been used in this figure to clarify the several interactions. In reality, many cells are adjacent to each other within the interaction area.
Mentions: Pilus-mediated interactions depend on the dynamics of pilus retraction [23] and on the spatial distribution of the fibrils to which the pilus tips have attached [24,25]. Although these factors are mechanically complex and not yet understood in detail, the interaction has straightforward effects. Pilus retraction provides a driving force for cell movement that happens to be large, several times larger than the force developed by muscle acto-myosin. And, because the force is almost never directed along the cell's long axis, the force tends to reorient the direction of gliding. Because we are confined by the approximation that isolated cells move with constant speed, we need only consider the reorienting effect of pilus retraction. No effect on cell speed is considered, except that it drops to zero when one cell collides with another. Inasmuch as the fibrils tend to bundle groups of cells, as will be described below, the large size of the cell cluster prevents a significant reorientation of the bundle; only the cell whose pili have attached is reoriented. We model the reorientation effect of pilus-mediated interactions as driving the local alignment of cells (see area I of Figure 4 and Methods). Although we represent the interaction area by a rectangle, a circle or some irregular domain could have been used. The important quality of an interaction domain is its area. That area is proportional to the probability that a cell has an interaction. Swarms of wild-type cells cover a larger area than those of A+S− or A−S+ mutants [11]. Moreover, the peninsulas are denser with cells that are well-aligned side by side [10]. Both effects illustrate reorientation due to pilus retraction. Cell clusters tend to be narrow in the case of an A+S− mutant and wide in the case of wild-type bacteria.

Bottom Line: Also, the model is able to quantify the contributions of S motility and A motility to swarming.Some pathogenic bacteria spread over infected tissue by swarming.The model described here may shed some light on their colonization process.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Notre Dame, Notre Dame, Indiana, United States of America.

ABSTRACT
Swarming, a collective motion of many thousands of cells, produces colonies that rapidly spread over surfaces. In this paper, we introduce a cell-based model to study how interactions between neighboring cells facilitate swarming. We chose to study Myxococcus xanthus, a species of myxobacteria, because it swarms rapidly and has well-defined cell-cell interactions mediated by type IV pili and by slime trails. The aim of this paper is to test whether the cell contact interactions, which are inherent in pili-based S motility and slime-based A motility, are sufficient to explain the observed expansion of wild-type swarms. The simulations yield a constant rate of swarm expansion, which has been observed experimentally. Also, the model is able to quantify the contributions of S motility and A motility to swarming. Some pathogenic bacteria spread over infected tissue by swarming. The model described here may shed some light on their colonization process.

Show MeSH