Dynamics of Bacterial Swarming

Abstract

When vegetative bacteria that can swim are grown in a rich medium on an agar surface, they become multinucleate, elongate, synthesize large numbers of flagella, produce wetting agents, and move across the surface in coordinated packs: they swarm. We examined the motion of swarming Escherichia coli, comparing the motion of individual cells to their motion during swimming. Swarming cells' speeds are comparable to bulk swimming speeds, but very broadly distributed. Their speeds and orientations are correlated over a short distance (several cell lengths), but this correlation is not isotropic. We observe the swirling that is conspicuous in many swarming systems, probably due to increasingly long-lived correlations among cells that associate into groups. The normal run-tumble behavior seen in swimming chemotaxis is largely suppressed, instead, cells are continually reoriented by random jostling by their neighbors, randomizing their directions in a few tenths of a second. At the edge of the swarm, cells often pause, then swim back toward the center of the swarm or along its edge. Local alignment among cells, a necessary condition of many flocking theories, is accomplished by cell body collisions and/or short-range hydrodynamic interactions.

Single-cell analysis in situ in a Bacillus subtilis swarming community identifies distinct spatially separated subpopulations differentially expressing hag (flagellin), including specialized swarmers

“…We now also demonstrate (Supplementary Movie File S3) that 168 sfp + swrA cells in dendrite tips move collectively as swirling and streaming packs. This behaviour is very similar to that of the E. coli swarmers described in three recent studies, all employing 90-100 % humidity (Copeland et al, 2010;Darnton et al, 2010;Turner et al, 2010;and see review by McCarter, 2010, and movie files accessible therein). Thus, dendritic migration for strain 168 sfp + swrA, which, in addition, we have shown is dependent on flagella and surfactin (Julkowska et al, 2005;Hamze et al, 2009), quite clearly shows all the generally accepted characteristics of swarming.…”

“…Another form of community swarming migration over a surface, apparently occurring in thin fluid films, requires flagella, a surfactant and the production of specialized swarmer cells (Harshey, 2003;Darnton et al, 2010).…”

Shape control and compartmentalization in active colloidal cells

“…Active matter covers a range of length scales that include molecular motors in the cytoskeleton (3)(4)(5), swimming bacteria (6)(7)(8), driven colloids (9,10), flocks of birds and fish (11)(12)(13)(14), and people and vehicles in motion (15). Over the last decade, studies of active matter have demonstrated behavior not seen in equilibrium systems, including giant number fluctuations (16,17), emergent attraction and superdiffusion (18)(19)(20), clustering (21,22), swarming (23)(24)(25)(26)(27), and self-assembled motifs (28,29).…”

Water reservoir maintained by cell growth fuels the spreading of a bacterial swarm

“…Much has been learned about the genetics and biochemistry of bacterial swarming as well as its relevance to biofilm formation and pathogenic infections (1)(2)(3). More recent advances have been made at the single-cell level (6)(7)(8)(9). However, relatively little is known about the thin layer of fluid that supports flagellar motility and allows swarm cells to maintain a distinct physiological state (10,11).…”