Studying the Mechanisms that Coordinate Multicellular Behavior in Bacterial Communities

Douglas Weibel
Assistant Professor of Biochemistry
University of Wisconsin- Madison

Bacteria sense surfaces and undergo physiological changes, which programs their growth and motility and coordinates their behavior. The resulting bacterial 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.

We study the mechanisms that bacterial cells use to coordinate their movement on surfaces. In contrast to our understanding of the biophysics involved in the motility of bacterial cells (e.g. Escherichia coli) in bulk fluids, almost nothing is known about the mechanisms that play a role in cell motility on surfaces. We are exploring two physical mechanisms that coordinate cellular movement on surfaces. In the first case, we study how bacteria sense surfaces and how contact with boundaries programs their morphological differentiation, which leads to changes in behavior. To carry this research out, we synthesize reversible polymers with defined chemical and physical properties and develop biophysical techniques for quantitatively analyzing the differentiation of entire communities of cells. In the second case, we study the dynamic bundling of flagella on adjacent cells to understand how these interactions coordinate the movement of differentiated cells and produce community-wide behavior. To explore this area we use a genetic/small molecule approach for creating cells of E. coli with fluorescence localized to the flagella and space- and time-resolved Förster resonance energy transfer (FRET) to measure interactions between flagella on neighboring cells.

In this talk I present recent work from our group on both of the cases described above and demonstrate that bacterial ‘swarming’ may be one of the most tractable experimental systems for identifying the mechanisms that drive systems toward emergent behavior. The models that emerge from these experiments may shed light on complex systems that exhibit non-linear behavior and extend far beyond microbes, and include developmental biology, distributed power networks, financial markets, and weather.

Refreshments to precede seminar in 226 Maryland Hall.
Please contact Erin Wilhelm at ewilhelm@jhu.edu if you have additional questions.