CLARK UNIVERSITY
PHYSICS COLLOQUIUM
Alexander Petroff
Center for Studies in Physics and Biology
Rockefeller University
Hydrodynamics and collective behavior
of two filter-feeding microbes
ABSTRACT: In their natural environments, microbes create fluid flows using cilia or
flagella that allow them to navigate ever-changing chemical gradients. Free-swimming
cells use this flow to move through the fluid. By contrast, filter-feeding microbes, which
typically live attached to a surface, create a fluid flow that actively transports chemicals to
the cell faster than diffusion, thus changing the chemical environment around the cell.
Because filter feeders are necessarily very powerful swimmers, these microbes exhibit
collective hydrodynamic phenomena inaccessible to many free-swimming microbes. Here
we investigate the collective dynamics displayed by two filter-feeding microbes, the
bacteria Thiovulum majus and the eukaryote Uronemella. We show that, although
phylogenetically very different, these two microbes are dynamically very similar. Both
form macroscopic communities that generate large-scale flows, which efficiently transport
nutrients. We show how both types of microbes exploit the flow of water and nutrients
around the community to coordinate the activity of the constituent cells, allowing the
community to be more than the sum of its parts. We then turn our attention to a novel form
of collective dynamics displayed by the bacteria T. majus. Cells spontaneously form twodimensional hexagonally-packed ``crystals,'' which slowly rotate. Thus, unlike the
typically chaotic motion found in microbial communities, T. majus cells organize into
highly structured arrangements. We discuss the dynamics shaping these crystals. These
results identify ecological and mathematically-tractable examples of non-equilibrium
pattern formation and provide insight into the collective dynamics of other microbial and
abiotic systems.
(Alexander P. Petroff, Xiao-lun Wu, Alexis Pasulka, & Albert Libchaber)
Wednesday, October 1, 2014
4:15 pm – Room S-122, Sackler Sciences Center