Living Hydrogel Biofilms

Title: Living hydrogel biofilms

 

Abstract: Bacterial biofilms are communities of adhered cells that thrive in nearly every environment. Within these communities, cells differentiate into heterogeneous states of physiology and gene expression. It is an open question how the conditions within biofilms, such as nutrient levels and cell density, control the phenotypic states of cells and, in turn, how these diverse cells determine the biofilm-level properties, such as 3D morphology. We ask this question in biofilms composed of diverse strains of Bacillus subtilis. Specifically, we investigate the formation of dormant spores within biofilms. We find that population-level sporulation rate depends strongly on cell-to-cell communication via quorum sensing. In strains with high cell density sensitivities, spores form rapidly, with biofilms expanding as narrow rings of vegetative cells that leave behind a spore-rich core. We investigate how this population of mostly dormant cells can create the wrinkled, 3D biofilm structures we observe. We find that before sporulation, cells secrete extracellular matrix polymers that turn biofilms into gels that wrinkle due to the competing effects of osmotic swelling and cross-linking. Mature B. subtilis biofilms are large assemblies of dormant spores embedded in self-produced hydrogel. Our results demonstrate the fundamental interplay of gene regulation and emergent physics in controlling the growth and form of cellular communities.

 

Bio: Joe Larkin is an interdisciplinary scientist who investigates how groups of bacteria use physics. He did his PhD in molecular biophysics fabricating systems for efficient capture of DNA and proteins for single-molecule analysis. As a postdoc, he became interested in bacterial physiology and now leads a group in the Departments of Biology and Physics at Boston University. The Larkin Lab aspires to learn how microbes exploit physics to perpetuate themselves in diverse environments. The lab uses time-lapse imaging and biophysical techniques to investigate the development of bacterial colonies and collaborates with theorists to build models that predict colony-level phenotypes from cell-level properties and interactions.