Spatio-Temporal Analysis of Cell-Cell Signaling in a Living Cell Microarray

Cell-cell signaling plays a central role in biology, enabling individual cells to coordinate their activities. For example, bacteria show evidence of intercellular signaling through \textit{quorum sensing}, a regulatory mechanism that launches a coordinated response, depending on the population density. To explore the spatio-temporal development of cell-to-cell signaling, we have created regular, heterotypic microarrays of living cells in hydrogel using time-multiplexed optical traps for submicron positional control of the cell orientation and location without loss of viability. We studied the \textit{Lux} system for quorum sensing; splitting it into sender and receiver plasmids, which were subsequently introduced into \textit{E. Coli}. Induced by IPTG, the sender cells express a fluorescent reporter (mRFP1) and the \textit{LuxI} enzyme that catalyzes the synthesis of a molecular signal AHL that diffuses through the cell membrane and the extra-cellular scaffold. The receiver cells collect the AHL signal that binds to the \textit{LuxR} regulator and reports it through GFP production. We have measured the time-delay between the onset of mRFP1 and GFP dependence on intercellular spacing in the array.