We report the design and characterization of microscale droplets of a thermotropic liquid crystal (LC) that respond to amphiphiles produced specifically by large groups or ‘communities’ of bacteria. Past reports demonstrate that aqueous dispersions of LC droplets undergo changes in internal configurations upon the adsorption of amphiphiles in ways that can be observed using polarized light. This behavior forms the basis of strategies for the real-time detection of environmental amphiphiles, including those produced by bacteria. Here, we demonstrate that droplets of LCs undergo ‘bipolar-to-radial’ configurations on exposure to amphiphiles that regulate bacterial quorum sensing (QS), a process by which bacteria communicate and carry out group activities, such as biofilm formation and virulence factor production. We demonstrate that LC droplets undergo bipolar-to-radial transitions on exposure to a series of acyl homoserine lactones (AHLs) that regulate QS in Gram-negative bacteria. By increasing AHL tail lengths from 4 to 12 carbons, we demonstrate that the concentration of AHLs required to promote these transitions decreases, allowing the transition to occur at 10 µM for the 12-carbon N-(3-oxo-dodecanoyl)-L-homoserine lactone, a natural QS signal in P. aeruginosa. Our results also reveal that these droplets respond to biologically relevant concentrations of the biosurfactant rhamnolipid, an amphiphile produced only by communities of P. aeruginosa under control of QS. Additional studies demonstrate that these droplets do not undergo bipolar-to-radial transitions in bacterial cultures growing at low population densities, but do undergo configurational changes as the bacteria grow and reach ‘quorate’ populations. These and other systematic studies using genetically engineered knock-out strains support the conclusion that these LC droplets respond selectively to the production of rhamnolipid and amphiphiles involved in the regulation of QS, and not other products produced by bacteria at lower sub-quorate densities. With further development, readily dispersed and environmentally stable droplet-based LC sensors could prove useful for the real-time monitoring of bacterial growth and virulence. More broadly, our results provide guidance for the design of new soft materials platforms that can sense, interact with, and respond selectively to large communities of bacteria engaged in collective group behaviors, including virulence factor production and biofilm growth.

Microscale droplets of thermotropic liquid crystals that respond to rhamnolipids and amphiphiles involved in the regulation of bacterial quorum sensing

2019 Spring National Meeting

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