Princeton University Department of Physics Colloquium

From the motions of the smallest enzymes to the growth of the tallest trees, biological organisms perform the amazing feats of life under the dictatorship of the laws of physics. These unbreakable rules define the space of successful solutions to biological problems and ultimately set limits on performance. Within this framework, living cells carry out a huge number of organized tasks over time. They multiply, absorb energy, copy and maintain genetic information, process input signals, make new materials, recycle and throw out old materials, move about, and talk to some cells while hiding from others. Each of these tasks requires the application of forces by specific machines at defined places inside and outside a cell. In contrast to our tremendous knowledge of these processes in eukaryotes such as humans, we know surprisingly little about how these forces are generated by tiny bacteria, the most populous group of organisms on our planet. My group is developing new techniques to study forces, dynamics and the three-dimensional localization of proteins in submicron-sized cells. I will briefly describe these efforts and then focus on our results on locomotive forces. We will discuss how Spiroplasma use a unique solution to the problem of swimming at vanishing Reynolds number and how Rickettsia rectifies Brownian fluctuations to achieve directed motion.