Electrical signaling and multicellular organization

Understanding the principles that govern the transition from stochastic individual cells to an organized collective is a general goal across many biological systems. For example, collective organization drives the development of an organism from a single embryo, and the emergence of intelligence from the activities of individual neurons. I propose to take a simplifying approach by studying bacteria as a model organism. While bacteria lack many specific features of higher organisms, they must cope with many of the same limiting resources—e.g., carbon, nitrogen and oxygen—since central metabolism is broadly conserved. Further, as many metabolites are charged, the maintenance of an electrical potential across the membrane imposes a constraint on cellular activity, regardless of species. Thus, we anticipate that features of collective organization discovered in bacteria may reveal principles underlying collective organization of cells in general. Bacteria have been used to understand fundamental mechanisms of cell biology. While bacteria are unicellular organisms that can exist in solitude, we now understand that the majority of undomesticated bacteria on our planet reside in biofilm communities. Biofilms share general traits associated with complex tissues such as differentiation, division of labor, and cooperation between differentiated cell types. Thus, the genetic tractability of bacteria and their ability to assemble biofilm communities may hold the key to understanding general principles of collective organization. However, the vast majority of bacterial research is still performed in liquid cultures using domesticated laboratory strains. In particular, limited experimental and optical accessibility of these densely packed communities has hindered the investigation of cellular dynamics during biofilm development. This proposal will overcome current limitations by advancing the measurement of biofilm dynamics at unprecedented resolution using novel microfluidic approaches and fluorescent reporter dyes. In this proposal, I will apply my engineering and mathematical modeling background to develop general insights into how bacteria coordinate their behavior in biofilms. Specifically, I propose to: (1) Develop a multi-scale imaging platform to obtain single cell resolution data of biofilms containing millions of cells. (2) Identify new fluorescent reporter dyes to quantitatively measure rapid (and previously invisible) metabolic dynamics in biofilms. Importantly, this proposal builds on my recent postdoctoral work where we have discovered that, similar to neurons in the brain, bacteria that reside in biofilms communicate via electrical signaling mediated by ion channels. This work will inspire future research directions, including: (3) Probing the electrical signaling mechanism by cloning ion channels and neuroscience pharmacology. (4) Modeling electrical signaling using a Hodgkin-Huxley inspired mathematical framework. (5) Developing a multi-colony device to test the range and generality of electrical signaling. For many years, the study of bacterial ion channels has provided fundamental insights into the structural basis of neuronal signaling. However, the native role of these ion channels in bacteria has remained elusive. Building off our recent advances in biofilm imaging, we have obtained preliminary results showing electrical signaling in biofilms. Moreover, this electrical signaling exhibits an unanticipated type of spatiotemporal dynamics in the form of sustained oscillations and traveling waves. Thus, bacterial ion channel