The Ecology of a Synthetic Biofilm: Synchronization without a Clock

Abstract

Biofilms are the archetype for smart materials where microcolonies of live bacteria and layers of dead cells are encapsulated in a hydrated matrix of polysaccharides, proteins and exopolymeric substances. We engineered synthetic biofilms to study their ecology_i.e. the cells’ relationship to each other and their environment. In particular, we investigated the physical parameters governing prokayrotic cell-to-cell signaling in a vascularized model of a biofilm, comprised of bacteria that are genetically engineered to transmit and receive so-called quorum-sensing signals based on the lux operon functionally linked to fluorescent reporters. Numerical modeling of these experiments reveals that gene expression is vitally dependent on the location within the biofilm and proximity to microchannels in the array, elements easily accessible in the model. Moreover, we observe synchronization in fluorescence from the microcolonies comprising the biofilm in a repetitive, pulsatile environment as shown in the figure. We find that the concentration of luxR mRNA varies measurably with C6HSL concentration and time indicating autoregulation of luxR. Moreover, flow cytometry data identifies two phenotypes in the cell population: one with a high C6HSL threshold; another with a lower threshold, indicating bi-stability associated with positive autoregulation of luxR.View Large Image | View Hi-Res Image | Download PowerPoint Slide