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...ns of the agents in these systems. Sematectonic and marker-based stigmergy differentiate between the forms of communication, that is, the types of signals that initiate a response or behaviour change =-=[15, 16, 19]-=-. Sematectonic stigmergy was first coined by Wilson and describes communication through physical changes to the Hindawi Publishing Corporation Scientifica Volume 2015, Article ID 387342, 8 pages http:...

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...that arise through an individual of the collective influencing the movement or behaviour of other individuals at a later point in time through the generation of persistent cues within the environment =-=[5, 6]-=-. The concept of stigmergy was first introduced by the entomologist Grassé in 1959 to explain the construction of termite colonies [5]. This powerful concept, for the first time, explained how appare...

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...ous (A) motility. Similar to twitching motility, S-motility is driven by the extension, binding, and retraction of tfp with this motility mode being typically displayed by groups or clusters of cells =-=[45, 46]-=-. A-motility mediates single cell migration and in contrast to that of S-motility, the machinery driving A-motility is yet to be confirmed and is an area of controversy [47, 48]. However all current s...

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...ative responses [16]. Finally, passive and active stigmergy have been described; however, as these two variations have for the most part been applied only to collective swarm intelligence in robotics =-=[12, 22]-=-, they will not be discussed here. Whilst there are many examples of self-organised multicellular behaviours of bacteria, the concept of stigmergy has rarely been used to describe these phenomena. Her...

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... these “swarming” behaviours of bacteria. Twitching motility is a mechanism of surface translocation that is powered by the extension, surface binding, and subsequent retraction of type IV pili (tfp) =-=[23, 24]-=-. Under appropriate conditions, twitching motility is as a complex, highly coordinated multicellular behaviour that leads to the active expansion of the bacterial community across solidified nutrient ...

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...that arise through an individual of the collective influencing the movement or behaviour of other individuals at a later point in time through the generation of persistent cues within the environment =-=[5, 6]-=-. The concept of stigmergy was first introduced by the entomologist Grassé in 1959 to explain the construction of termite colonies [5]. This powerful concept, for the first time, explained how appare...

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... these “swarming” behaviours of bacteria. Twitching motility is a mechanism of surface translocation that is powered by the extension, surface binding, and subsequent retraction of type IV pili (tfp) =-=[23, 24]-=-. Under appropriate conditions, twitching motility is as a complex, highly coordinated multicellular behaviour that leads to the active expansion of the bacterial community across solidified nutrient ...

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...collective these swarmer cells rapidly migrate across the surface until they differentiate back to the nonmotile normal cells resulting in consolidation and the formation of the observed ring pattern =-=[41, 42]-=-. The flagella of Proteus swarmer cells interweave with flagella from the same cell and with those of neighbouring cells, forming a connected and highly synchronised swarming front that aids in the ra...

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...urn onto the trails rather than migrating across virgin territory. Continued cellular traffic along the trails results in their thickening and extension as a consequence of continued slime deposition =-=[51, 53]-=-. It is recognised that this trail following behaviour coordinates the collective behaviour of M. xanthus cells, specifically those displaying A-motility, at the leading edge of the surface swarms, an...

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...collective these swarmer cells rapidly migrate across the surface until they differentiate back to the nonmotile normal cells resulting in consolidation and the formation of the observed ring pattern =-=[41, 42]-=-. The flagella of Proteus swarmer cells interweave with flagella from the same cell and with those of neighbouring cells, forming a connected and highly synchronised swarming front that aids in the ra...

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... active surface migration by Paenibacillus vortex biofilms occurs as a consequence of the actions of a subpopulation of filamentous cells that direct the motion of the other members of the collective =-=[54, 55]-=-. This appears to be another example of bacterial stigmergy, though it remains to be determined if this collective behaviour occurs as a consequence of physical alteration of the environment, slime, o...

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... refers to communication through the deposition of chemical signals within the environment [15, 16, 19], for example, the following of pheromone trails by ants aiding in their food foraging behaviour =-=[21]-=-. A further distinction between these two variations is that for sematectonic stigmergy the communicative information tends to provide a direct contribution to the task/emergent property, whereas in m...

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...urn onto the trails rather than migrating across virgin territory. Continued cellular traffic along the trails results in their thickening and extension as a consequence of continued slime deposition =-=[51, 53]-=-. It is recognised that this trail following behaviour coordinates the collective behaviour of M. xanthus cells, specifically those displaying A-motility, at the leading edge of the surface swarms, an...

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...r cells interweave with flagella from the same cell and with those of neighbouring cells, forming a connected and highly synchronised swarming front that aids in the rapid expansion by these colonies =-=[43]-=-. The secretion of an extracellular slime has been found to facilitate the collective swarming behaviour of Pr. mirabilis. At the leading edge of Pr. mirabilis swarms, swarmer cells are encased in a s...

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... this EPSmatrix is essential for biofilm development as it provides intercellular connectivity that binds cells to each other and, in the case of surface-attached biofilms, provides surface adherence =-=[60, 61]-=-. The ability of the EPS matrix produced by biofilm cells to promote cohesion and surface attachment of the biofilm community is an example of sematectonic stigmergy. It has been observed that individ...

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...ing of trails by herd animals, pedestrians, and hikers [7] and the construction of wasp nests, where the development of the physical structure acts as cues for the next steps or process in the design =-=[6, 20]-=-. In contrast, marker-based stigmergy refers to communication through the deposition of chemical signals within the environment [15, 16, 19], for example, the following of pheromone trails by ants aid...

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...s. At the leading edge of Pr. mirabilis swarms, swarmer cells are encased in a slime layer and appear to preferentially move along an interconnected network of phase bright slime trails (Figure 1(d); =-=[44]-=-). It has been hypothesised that the slime trails aid in directing swarming motility and the slime encasement facilitates the maintenance of a cohesive organisation of cells [42, 44]. Therefore slime ...

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...s or clusters of cells [45, 46]. A-motility mediates single cell migration and in contrast to that of S-motility, the machinery driving A-motility is yet to be confirmed and is an area of controversy =-=[47, 48]-=-. However all current schools of thought predict the role of a secreted slime in facilitating the A-motility of this organism [49– 51], where phase bright trails are observed at the leading edge of th...

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...s or clusters of cells [45, 46]. A-motility mediates single cell migration and in contrast to that of S-motility, the machinery driving A-motility is yet to be confirmed and is an area of controversy =-=[47, 48]-=-. However all current schools of thought predict the role of a secreted slime in facilitating the A-motility of this organism [49– 51], where phase bright trails are observed at the leading edge of th...

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...ology, and computer sciences [15, 16, 72]. The wide acceptance of stigmergy can, for the most 6 Scientifica part, be attributed to a special edition of Artificial Life dedicated to stigmergic systems =-=[6, 73]-=-, with the hopes of bringing this concept to the forefront within the scientific community. This concept, despite its obvious application to the understanding of multicellular bacterial behaviours, ha...

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...ve shown recently that the emergence of the interconnected network of trails is likely to occur due to the formation of an interconnected furrow system in the underlying semisolid media (Figure 1(b); =-=[28, 29]-=-). We recently applied the concept of stigmergy to describe the emergent selforganisation of P. aeruginosa interstitial communities that occurs as a consequence of cells creating and travellingwithin ...

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...ative responses [16]. Finally, passive and active stigmergy have been described; however, as these two variations have for the most part been applied only to collective swarm intelligence in robotics =-=[12, 22]-=-, they will not be discussed here. Whilst there are many examples of self-organised multicellular behaviours of bacteria, the concept of stigmergy has rarely been used to describe these phenomena. Her...

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...ns of the agents in these systems. Sematectonic and marker-based stigmergy differentiate between the forms of communication, that is, the types of signals that initiate a response or behaviour change =-=[15, 16, 19]-=-. Sematectonic stigmergy was first coined by Wilson and describes communication through physical changes to the Hindawi Publishing Corporation Scientifica Volume 2015, Article ID 387342, 8 pages http:...

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...many bacterial communities quorum sensing regulates and coordinates social behaviours, such as bioluminescence, secretion of public goods, and the switch from planktonic to the biofilm mode of growth =-=[69]-=-. Quorum sensing occurs through the release of small molecules by individual bacteria into the environment by passive diffusion. The concentration of these small molecules increases within the environ...

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...n density, a gene regulation cascade is initiated culminating in the up- or downregulation of the expression of various genes required for social behaviours, virulence factor production, and so forth =-=[69, 70]-=-. In this manner it has been identified that quorum sensing can regulate the expression of over 300 genes within P. aeruginosa [69]. Quorum sensing within bacterial communities bares a striking resemb...

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...has been speculated that the agar polysaccharides may act as ligands to which the tfp bind and that the physical interaction of the tfp with the agar may be responsible for the agar pitting phenotype =-=[32]-=-. It is interesting to speculate that the formation of furrownetworks may constitute a more global mechanism for the stigmergic organisation of bacterial communities. We have recently also identified ...

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...d directing cellular migration to these areas [67]. In areas of high Psl concentration, cells were observed to adhere to the substratum and correlated to the subsequent sites of microcolony formation =-=[67, 68]-=-. This mechanism of following exopolysaccharide trails to coordinate the single cellular motilities of P. aeruginosa during early biofilm development is an example of sematectonic and quantitative sti...

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...ous (A) motility. Similar to twitching motility, S-motility is driven by the extension, binding, and retraction of tfp with this motility mode being typically displayed by groups or clusters of cells =-=[45, 46]-=-. A-motility mediates single cell migration and in contrast to that of S-motility, the machinery driving A-motility is yet to be confirmed and is an area of controversy [47, 48]. However all current s...

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...ecreted slime in facilitating the A-motility of this organism [49– 51], where phase bright trails are observed at the leading edge of the M. xanthus swarms when grown on semisolid media (Figure 1(e); =-=[52]-=-), similar to that of Pr. mirabilis. M. xanthus cells preferentially migrate along these slime trails, with cells frequently observed to turn onto the trails rather than migrating across virgin territ...

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...In biological systems, the coordination of group behaviours and the subsequent emergence of large-scale patterns are inherently more complex than that which spontaneously emerges in nonliving systems =-=[1]-=-, involving an interplay of physical, chemical, and biological interactions, both physiological and behavioural, that have been honed through natural selection [2–4]. Many self-organised phenomena in ...

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...ulties in modelling biological systems, a number of these models do not truly reflect experimental observations or contain artefacts as a consequence of the rule parameters incorporated into themodel =-=[59]-=-. Stigmergic systems have long been the focus of extensive computational modelling to understand the emergent properties within these systems [7–10] and to relate stigmergic principles from one system...

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...isms is gaining interest within the scientific community. A recent review has called for the employment of a more integrative approach across scientific fields in the study of self-organising systems =-=[71]-=-. Stigmergy provides an excellent example of this approach where, since its first introduction within the field of entomology [5], the importance of this concept has been recognised across diverse are...

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...rst introduction within the field of entomology [5], the importance of this concept has been recognised across diverse areas ranging from biology to social sciences, technology, and computer sciences =-=[15, 16, 72]-=-. The wide acceptance of stigmergy can, for the most 6 Scientifica part, be attributed to a special edition of Artificial Life dedicated to stigmergic systems [6, 73], with the hopes of bringing this ...

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...phological features including large vanguard rafts of highly aligned cells at the leading edge behind which there is an intricate, interconnected lattice-like network of trails of cells (Figure 1(a); =-=[25]-=-). Semmler et al. proposed that as the vanguard rafts migrated across the surface of the semisolid nutrient media, they created some form of trail along which ensuing cells preferentially followed [25...

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...ion of the characteristic interconnected pattern network of these biofilms [28]. To understand the role of eDNA within these biofilms we employed a computer vision and cell tracking analysis pipeline =-=[28, 37, 38]-=- to quantitate the behaviour of the individual cells in the absence and presence of DNaseI. Interrogation of the resulting image informatics database revealed that eDNA facilitates twitching motility-...

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...e identified that P. aeruginosa tfp bind to DNA [39] and that P. aeruginosa cells spontaneously pneumatically orient with the direction of extended DNA chains in a matrix of aligned, concentrated DNA =-=[40]-=-. We proposed that the bed of aligned eDNA molecules within P. aeruginosa interstitial biofilms maintains cell orientations by aligning cells to the thin strands of eDNA and that eDNA provides a subst...

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... active surface migration by Paenibacillus vortex biofilms occurs as a consequence of the actions of a subpopulation of filamentous cells that direct the motion of the other members of the collective =-=[54, 55]-=-. This appears to be another example of bacterial stigmergy, though it remains to be determined if this collective behaviour occurs as a consequence of physical alteration of the environment, slime, o...

Citation Context

... this EPSmatrix is essential for biofilm development as it provides intercellular connectivity that binds cells to each other and, in the case of surface-attached biofilms, provides surface adherence =-=[60, 61]-=-. The ability of the EPS matrix produced by biofilm cells to promote cohesion and surface attachment of the biofilm community is an example of sematectonic stigmergy. It has been observed that individ...

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...posited trails of the exopolysaccharide Psl, which appeared to recruit additional cells along these trails leading to a positive feedback loop of further Psl deposition and subsequent cell attraction =-=[67]-=-. It was hypothesised that this trail following behaviour was facilitated by twitchingmotility-mediated surface exploration, where the tfp were thought to probe the surrounding areas for Psl networks,...

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...derstand the emergent properties within these systems [7–10] and to relate stigmergic principles from one system to another in an attempt to draw comparisons from well-studied and established systems =-=[17]-=-. It is our contention that a similar approach could be taken for modelling bacterial swarming communities through the incorporation of key ideas from other stigmergic models, such as those of Helbing...

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... and computing [12–17]. Interestingly, even the development of multicellular tissues has been described as a stigmergic phenomenon in which chemical cues are embedded in extracellular matrix material =-=[18]-=-. As other scientific fields such as social sciences, technology, and computer sciences began adopting the concept of stigmergy to help describe and explain various phenomena of emergent behaviour or ...

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... bacteria employ to control multicellular activities. Furthermore, we suggest that bacterial stigmergic systemsmay provide testable models to explore stigmergic self-organisation at a molecular level =-=[29]-=-, which is currently an unexplored concept and will ultimately lead to greater understanding of other biological stigmergic systems. Understanding the mechanisms employed by bacteria to coordinate the...

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...anism, Dichelobacter nodosus, also produces striking interconnected pattern networks reminiscent of that of P. aeruginosa when they are grown at the interstitial space between the petri dish andmedia =-=[36]-=-. However, whether this emergent pattern arises due to the corrosion of the agar during biofilm expansion, creating furrows that guide the movements of the bacteria remains to be determined. The agar ...

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...ion of the characteristic interconnected pattern network of these biofilms [28]. To understand the role of eDNA within these biofilms we employed a computer vision and cell tracking analysis pipeline =-=[28, 37, 38]-=- to quantitate the behaviour of the individual cells in the absence and presence of DNaseI. Interrogation of the resulting image informatics database revealed that eDNA facilitates twitching motility-...

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...iods. These analyses also revealed that eDNA is required for maintaining coherent cell behaviour and cell alignment over time [28]. Previous reports have identified that P. aeruginosa tfp bind to DNA =-=[39]-=- and that P. aeruginosa cells spontaneously pneumatically orient with the direction of extended DNA chains in a matrix of aligned, concentrated DNA [40]. We proposed that the bed of aligned eDNA molec...