Determining biophysical mechanisms of phenotypic segregation in bacterial biofilms with agent-based models

Bacteria often exist as surface-adhered communities called biofilms that are embedded within extracellular matrices of polymeric substances. Experimental efforts to dissect the molecular processes underlying the biofilm life cycle have uncovered many signaling pathways in various species, but we lack a comprehensive understanding of how these pathways dictate the biofilm’s architecture. Here, we discuss the consequences of spatiotemporal heterogeneity in intracellular signaling on the architecture of biofilms formed by the model species Vibrio cholerae. Recent work has shown that growing V. cholerae biofilms exhibit cell-to-cell bimodality in the intracellular signaling of the key second messenger cyclic diguanylate (c-di-GMP), which governs the transition between planktonic and sessile phenotypes by regulating matrix component production. Moreover, cells with different c-di-GMP levels spatially segregate during biofilm growth, as cells with low c-di-GMP are pushed towards the periphery and give rise to a concentration of cells with high c-di-GMP in the biofilm’s core. Using agent-based models that integrate c-di-GMP signaling and its effects on cellular physiology with the mechanics of biofilm growth, we reveal the biophysical mechanisms underlying this spatial segregation. We discuss the broader consequences of cell-to-cell heterogeneity on biofilm architecture and the utility of agent-based modeling as a tool for investigating emergent properties of microbial communities.