POSTERS - BLAST X - University of Utah

BLAST X Poster #44
A CROSS-SPECIES COMPARISION OF CHEMOTACTIC BEHAVIOR
Julie Simons and Paul Milewski
University of Wisconsin—Madison, Department of Mathematics, 480 Lincoln Dr., Madison, WI
53706
Understanding the population-level behavior of bacteria is of importance not only in
exploring how simple organisms can perform complex behavior, but also to be able to optimize
their potential for bioremediation and other uses. We are interested in modeling the
chemotactic behavior of Rhodobacter sphaeroides and the better-understood Escherichia coli
using a partial differential equation model known as the Keller-Segel model and experimental
data, with the aim of being able to make a cross-species comparison. Swarm-plate experiments
with uniform concentrations of the chemoattractant L-aspartate were performed for both bacteria
over several concentrations of aspartate. Separately, growth experiments in liquid cultures were
undertaken to quantify differences in aspartate concentration dependent growth between the
two species. From the data we are able to determine parameter values for a Keller-Segel model
and thus quantify differences between non-chemotactic diffusive behavior, growth effects, and
chemotactic behavior. This quantitative modeling work comparing population-level behavior of
these bacteria allows one to deduce metabolic function parameters in agar, which are not
possible to find experimentally and not incorporated in many previous models. We find that a
significant proportion of the E. coli wild-type population appears to be non-chemotactic whereas
the R. sphaeroides wild-type population appears to be primarily chemotactic, something not
explored in other studies. Our parameters also indicate a joint saturation of growth and
chemotaxis, which we postulate is a common evolutionary result. These findings provide a
platform from which to explore incorporating cell-level knowledge into macro-scale behavioral
models and the effects of heterogeneity of populations.
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