The post-fragmentation density function for bacterial aggregates

Start: 11/16/2011 - 1:15pm
End  : 11/16/2011 - 1:25pm

Applied Math Seminar

Erin Byrne, HMC


Multicellular communities are a dominant, if not the predominant, form
of bacterial growth. Growing affixed to a surface, they are termed
biofilms. When growing freely suspended in aqueous environments, they
are usually referred to as flocs. Flocculated growth is important in
conditions as varied as bloodstream infections (where flocs can be
seen under the microscope) to algal blooms (where they can be seen
from low earth orbit). Understanding the distribution of floc sizes in
a disperse collection of bacterial colonies is a significant
experimental and theoretical challenge. One analytical approach is the
application of the Smoluchowski coagulation equations, a group of PDEs
that track the evolution of a particle size distribution over time.

The equations are characterized by kernels describing the result of
floc collisions as well as hydrodynamic-mediated fragmentation into
daughter aggregates. The post-fragmentation probability density of
daughter flocs is one of the least well-understood aspects of modeling
flocculation. A wide variety of functional forms have been used over
the years for describing fragmentation, and few have had experimental
data to aid in its construction. In this talk, we discuss the use of
3D positional data of Klebsiella pneumoniae bacterial flocs in
suspension, along with the knowledge of hydrodynamic properties of a
laminar flow field, to construct a probability density function of
floc volumes after a fragmentation event. Computational results are
provided which predict that the primary fragmentation mechanism for
medium to large flocs is erosion, as opposed to the binary
fragmentation mechanism (i.e. a fragmentation that results in two
similarly-sized daughter flocs) that has traditionally been assumed.

Davidson, CMC

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