DEPARTMENT OF MATHEMATICAL & STATISTICAL SCIENCES

UNIVERSITY OF ALBERTA

**MATHEMATICAL
BIOLOGY SEMINAR**

MONDAY, NOVEMBER 4, 2002

3:00 PM

CAB
657

**Dr. ****R.
Tyson**

Department of Mathematics and Statistics

** **Okanagan
University College

A Minimal Mechanism of Bacterial
Pattern Formation

Colonies
of *Escherichia coli* or *Salmonella typhimurium* form geometrically complex patterns
when exposed to, or feeding on, intermediates of the tricarboxylic acid (TCA)
cycle. In response to the TCA cycle
intermediate, the bacteria secrete aspartate, a potent chemoattractant. As a result, the cells form
high-density aggregates arranged in striking regular patterns. The simplest are temporary spots formed
in a liquid medium by both *E.** **coli* and *S.** **typhimurium*. In semi-solid medium *S.** **typhimurium* forms concentric rings arising from
a low-density bacterial lawn, which are either continuous or spotted. In contrast, *E.** **coli* forms complex patterns arising from
a dense swarm ring, including interdigitated spots (also called sunflower
spirals), radial spots, radial stripes and chevrons. We present a mathematical model that captures all three of
the pattern-forming processes experimentally observed in both *E.** **coli* and *S.** **typhimurium*, using a minimum of assumptions.

This seminar is
partially funded by the Pacific Institute for the Mathematical Sciences (PIMS)