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Two Equations...Many Curves

Pathogenic Listeria monocytogenes move through an infected cell by "building a tail, bit by bit"...forming circles, slaloms, S-curves, figure eights, and loop-the-loops (when squashed on a microscopic slide). How does one explain or model the visual pattern?

Vivek Shenoy (Brown University engineer) and Julie Theriot (Stanford University scientist) have created a simple mathematical description of the observed movements of the Listeria monocytogenes. They were surprised that it only required one pair of equations and only two key variables. And now, their models are helping to identify bacterial mutants, as the equations suggest which mechanisms could be driving the motion.

In the diagram below, the red lines are the predicted paths using the two mathematical equations, which can represent all the observed motions of the Listeria monocytogenes (blue or green lines). Because mutant strains do not move in ways predicted by the equations, researchers can identify and study them.

Source: H. Fountain's "Observatory," New York Times, May 22, 2007