Mechanisms of Extracellular Matrix-Mediated Electrochemical Signaling

While bacteria are single-celled organisms, in nature they exist within multicellular biofilms that can exhibit sophisticated emergent behaviors through cell-to-cell coordination. As high-throughput DNA sequencing continues to reveal widespread microbial diversity in the environment and the human microbiome, understanding and predicting their emergent behaviors is the current frontier of the field. To better understand these emergent behaviors, we have recently developed a microfluidic-based method for gathering quantitative single-cell level measurements from biofilms. In particular, we recently made the discovery of potassium ion-channel mediated electrochemical signaling in model Bacillus subtilis biofilm communities. Specifically, we found that metabolic stress induces the release of intracellular potassium via the ion-channel YugO, which in turn depolarizes and triggers release of potassium from neighboring cells, creating a positive feedback loop that results in biofilm-wide extracellular potassium waves. This cell-to-cell signaling process is associated with increased fitness of the community, since coordinating metabolism among the population allows the biofilm to give its sheltered interior cells increased access to nutrients. Here, we propose to determine how this potassium-based signaling process is directed by structural features of the biofilm that may interact with electrochemical species like potassium. Specifically, we are focusing on the extracellular matrix, a heterogeneous scaffold comprised of multiple negatively-charged components including polysaccharides, proteins, and extracellular DNA. Based on its opposite electrical charge, we hypothesize that the matrix can direct the diffusion of positively charged potassium ions, thereby allowing matrix patterning to modulate the speed of electrochemical signaling and its localization to particular subsets of cells. Our preliminary unpublished findings suggest that vein-like matrix patterns are associated with heterogeneous electrochemical signaling in biofilms. Therefore, we propose to test the hypothesis that biofilms use the matrix as a conduit to target electrochemical signals to specific subsets of cells. To accomplish this, we will 1) Quantitatively characterize matrix pattern formation in biofilms; 2) Establish a causal link between matrix patterns and electrochemical signaling. By analogy to how a circuit board guides electronic signals, matrix patterning could guide electrochemical signals to distinct regions of the biofilm. Such a phenomenon would represent a previously undescribed form of emergent control over cell-to-cell signaling in bacterial biofilms.