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<b>Complex Systems Seminar</b><br><i>Studying the Origins of Emergent Behavior in Populations of Bacteria</i>

Monday, November 9, 2009
5:00 AM
335 West Hall

Speaker: Doug Weibel (University of Wisconsin)

Bacteria sense surfaces and undergo physiological changes, which programs their growth and motility and coordinates their behavior. The resulting communities display ‘emergent’ properties in which the coordination of the behavior of cells is not predictable from the sum of the individual components (e.g. cells). The resulting structures behave as multicellular organisms and collectively colonize niches in search of nutrients and other growth factors. The transition of a group of ‘individual’ bacterial cells to collective, multicellular behavior is accompanied by the upregulation of pathogenic factors, suggesting that in this state, the organisms are preparing to invade a host. An understanding of the mechanisms that control and regulate the switch from individual behavior to multicellular behavior will identify mechanisms and targets that may play a role in preventing and treating microbial pathogenesis.

Dr. Weibel's team is particularly fascinated by the mechanisms that cells use to coordinate their movement on surfaces. In contrast to the understanding of the biophysics involved in the motility of bacterial cells (e.g. Escherichia coli) in bulk fluids, very little information is available on the mechanisms that play a role in cell motility on surfaces. Dr. Weibel's team is exploring two physical mechanisms that may play a role in the coordination of cellular movement on surfaces based on two very different physical interactions. In the first case, they are exploring how bacteria sense surfaces and how contact with boundaries programs their morphological differentiation into cells that move collectively on surfaces. To carry this research out, Dr. Weibel's team synthesize polymers with defined chemical and physical properties and are using biophysical tools to measure their differentiation quantitatively. In the second case, they are exploring whether the cooperative movement of differentiated cells arises through the dynamic bundling of flagella on adjacent cells. To test this hypothesis, his team has developed a genetic/small molecule approach for creating cells of E. coli with fluorescence localized exclusively to the flagella, and are using space- and time-resolved Förster resonance energy transfer (FRET) to measure interactions between flagella on neighboring cells.

In this talk, Professor Weibel will present recent work from his group on both mechanisms and demonstrate that bacterial ‘swarming’ may be one of the most tractable experimental systems for identifying the mechanisms that drive systems toward emergent behavior. These experiments may shed light on systems that extend far beyond microbial systems, and include financial markets, weather, and population dynamics.