Abstract: Budding yeast contain many organelles surrounded by lipid membranes. At a particular stage in the yeast's life, lipids and proteins in one of these membranes phase separate into huge, micron-scale liquid domains. This phase separation is functionally important, enabling yeast survival during periods of stress. We found that this miscibility transition is reversible with temperature, as would be expected from equilibrium thermodynamics, even though it occurs in a living system. We also found that yeast actively regulate this phase transition to hold the membrane transition ~15˚C above the yeast growth temperature. The transition appears to be correlated with a change in the membrane's lipid composition that maximizes differences in orientational order of the lipid's carbon chains.

Bio: Sarah L. Keller, the Duane and Barbara LaViolette Professor of Chemistry, is a biophysicist at the University of Washington in Seattle. She investigates self-assembly, complex fluids, and soft matter systems. Her research group’s primary focus concerns how lipid mixtures within bilayer membranes give rise to complex phase behavior. She is a Fellow of the American Physical Society and a Fellow of the Biophysical Society.

Abstract: Bacteria are arguably the simplest form of life; and yet, as multi-cellular collectives, they perform complex functions critical
to environment, food, health, and industry. What principles govern how complex behaviors emerge in bacterial collectives? And how can we harness them to control bacterial behavior? In this talk, I will describe my group's work addressing this question using tools from soft matter engineering, 3D imaging, and biophysical modeling. We have developed the ability to (i) directly visualize bacteria from the scale of a single cell to that of an entire multi-cellular collective, (ii) 3D-print precisely structured collectives, and (iii) model their large-scale motion and growth in complex environments. I will describe how, using this approach, we are developing new ways to predict and control how bacterial collectives — and potentially other forms of "active matter" — spread large distances, adapt shape to resist perturbations, and self-regulate growth to access more space by processing chemical information in their local environments.

Bio: Sujit Datta is a Professor of Chemical Engineering, Bioengineering, and Biophysics at the California Institute of Technology (Caltech), where he moved in September 2024. He was previously on the faculty at Princeton, where he started as Assistant Professor of Chemical and Biological Engineering in 2017, and then was promoted to Associate Professor and Director of Graduate Studies in 2023. Sujit earned a BA in Mathematics and Physics and an MS in Physics in 2008 from the University of Pennsylvania, and then a PhD in Physics in 2013 from Harvard, where he studied fluid dynamics and instabilities in soft and disordered media with Dave Weitz. His postdoctoral training was in Chemical Engineering at Caltech, where he studied the biophysics of the gut with Rustem Ismagilov. Sujit's lab studies the dynamics, self-organization, and applications of soft (“squishy”) and living systems—complex fluids, gels, and bacterial communities/active matter—in complex environments, motivated by challenges in biotechnology, energy, environment, and medicine. His scholarship has been recognized by awards from a broad range of different communities, reflecting its multidisciplinary nature, including through the AIChE Allan Colburn and 35 Under 35 Awards, ACS Unilever Award, Camille Dreyfus Teacher-Scholar Award, three awards from the APS (Early Career Award in Biological Physics, Andreas Acrivos Award in Fluid Dynamics, and the Apker Award), the Arthur Metzner of the Society of Rheology, Pew Biomedical Scholar Award, NSF CAREER Award, and multiple commendations for teaching.