A Synthetic Quorum Sensing System Reveals Interaction Between Extracellular Matrix and Quorum Sensing Molecules
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Even though bacteria are unicellular organisms, they commonly reside in structured communities known as biofilms. One of the defining characteristics of biofilms is the presence of an extracellular matrix (ECM) that encapsulates all cells within the community and provides the biofilm with structural integrity. The production and degradation of ECM components are often regulated by quorum sensing (QS), a prevailing cell-cell communication method between bacterial cells. Quorum sensing allows bacteria to communicate with each other by secreting and sensing small molecules called quorum signals. The literature suggests that the ECM may affect diffusion of quorum molecules through a physical connection between these processes. However, since QS regulates ECM expression, ECM expression and QS are tightly coupled and cannot be perturbed independently. Here we constructed a synthetic QS system in Bacillus subtilis to overcome this limitation and investigate whether ECM production affects QS signals, by quantitatively measuring the synthetic QS response in biofilm communities and single cells. Specifically, we constructed a synthetic quorum-sensing system with designated "Sender" and "Receiver" cells in Bacillus subtilis. This synthetic QS system allowed us to uncouple and independently investigate ECM production and QS in both biofilms and single cells. Our results showed that ECM-producing cells have a higher gene expression response to QS signals. The enhanced QS response suggests a private benefit for ECM-producing cells, which may indicate another mechanism to balance the cost of ECM production and constrain ECM production cheaters in biofilms.