Theoretical Problems in Soft Matter and Quantitative Biology

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TECHNICAL SUMMARYThis award supports theoretical research and education at the interface between materials science, statistical physics and biophysics. The PI will study dislocation-mediated elongation and bending of rod-shaped bacterial cell walls, and related phenomena in colloidal particle assemblies adsorbed on cylinders. In the case of bacteria, remarkable glycan strand extension machinery powers systematic dislocation climb, leading to growth dynamics with few analogs in conventional materials science. Dislocation trajectories should be influenced by long-range elastic interactions and by external stresses and turgor pressure via the Peach-Kohler force. Glide dynamics dominates for colloids on solid cylinders. Because isolated dislocations with Burgers vectors along the cylinder axis behave like compact grain boundaries, separation via glide may be able to mediate transitions between different phyllotactic particle packings.In another thrust, the PI will use the tools of non-equilibrium statistical dynamics, population genetics and probability theory to address issues related to migrations, competition and cooperation. These phenomena have played a crucial role in the history of many species, on both solid surfaces, as in migrations of invasive species, or bacterial invasions of animal tissue, and in liquid environments such as the ocean, where photosynthetic organisms such as cyanobacteria and phytoplankton compete in the presence of fluid advection. With range expansions in mind, the PI will study how mutualistic competitions between microorganisms play out in solid environments in two and three dimensions, with a particular emphasis on the effect of front undulations combined with inflationary dynamics. Because much of earth's evolutionary history took place in rivers, lakes and oceans, the PI will also study fixation times and probabilities for discrete organisms that reproduce and compete subject to advecting fluid flows, including high Reynolds number turbulence. Especially interesting phenomena arise for microorganisms whose doubling times are in the middle of a Kolmogorov-like cascade of eddy turnover times. This project provides an unusual interdisciplinary environment to educate and train students in modern condensed matter theory, materials theory, statistical physics, and biological physics to bring theory to bear, in part, on problems related to the environment, sustainability, and biologically inspired materials.NONTECHNICAL SUMMARYThis award supports theoretical research and education at the interface between materials science, statistical physics and biophysics. Cooperation among microorganisms is at the heart of many complex systems. For example, gut bacteria can help animal hosts digest cellulose. On an ecosystem level, plants often rely on fungi to receive important nutrients. Even human societies are products of cooperation between individuals. Despite the apparent advantage and pervasiveness of mutualism, its existence is often difficult to explain: Cooperation can succumb to cheating and to stochastic number fluctuations. A detailed theory of how microorganisms on solid surfaces and in dynamic environments such as the ocean compete and cooperate will lead to a better understanding of the ecology of our planet and living matter with implications for advanced materials inspired by biological organisms. This research is also important to advance understanding of how cell walls endow growing microorganisms with a shape and strength. Of particular interest are gram-negative bacteria, whose cell walls consist of a thin meshwork of soft strands composed of large chain-like molecules. An improved understanding of growth mechanisms could lead to more efficient antibiotics, and better remediation of human and animal diseases.This project provides an unusual interdisciplinary environment to educate and train students in modern condensed matter theory, materials theory, statistical physics, and biological physics to bring theory to bear, in part, on problems related to the environment, sustainability, and biologically inspired materials.