Emergent behavior of bacterial collectives : Pseudomonas aeruginosa interstitial biofilms
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In this work, I discuss my investigation into the collective behavior of Pseudomonas aeruginosa interstitial biofilms, bacterial systems that exhibit a unique variety of pattern formation. The patterns appear to emerge through some form of stigmergy, a term that applies to processes in which the action of an individual leaves a trace in a medium that modifies or stimulates the performance of other actions in the modified location. The term was invented to describe the self-organization processes used by insects such as termites or ants. For the present investigation, I developed a novel agent-based computer simulation of bacterial behavior that explicitly simulates two distinct stigmergy mechanisms. One of these is biological while the other is physical, and the two are mechanistically independent. The physical stigmergy mechanism arises from the deformation of the medium over which the bacteria move, and depends sensitively on the material properties of this medium. The biological stigmergy mechanism arises from secretion and deposition of extracellular polymeric substances that increase the movement rate of bacteria encountering them. My results reveal that neither of these processes alone is sufficient for the formation of the observed patterns. Instead, the morphogenesis mechanism arises from an emergent interplay between them.
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