| Speaker: | John Kessler ( Physics, University of Arizona, Tucson, Arizona) | |||
| Title: | Individual and collective dynamics of swimming bacteria |
| Abstract: |
Concentrated bacteria Bacillus subtilis exhibit remarkable collective
dynamics. Self-organized domains, approximately close-packed, move with
velocities that can be greater than the swimming speeds of individual
cells. Domains form, break up, re-form and produce evanescent colliding
vortical structures. Passive tracers were used to acquire Particle
Imaging Velocimetry (PIV) analyses of flow fields, advective transport,
spatial and temporal correlation functions. Hydrodynamic interactions and
steric repulsion of the rod-shaped bacteria are the basis of the
collective dynamics of this Zooming BioNematic Phase (ZBN). Steric
repulsion accounts for non-polar (Onsager/Flory) alignment. Flipping of
individual cells' flagella and tendency to orient and swim upstream will be
demonstrated. These latter phenomena can account for quorum polarity, a
crucial ingredient for formation of the ZBN. Individual cells swimming
adjacent to a surface tend to continue swimming parallel to it. Pairs of
cells tend to continue swimming adjacent to one another. The fundamental
hydrodynamics of these phenomena, also fundamental ingredients toward a
theory of the ZBN, has been modeled by Ricardo Cortez in a series of
beautiful, instructive, idealized calculations, some
of which will be shown.
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