Abstract
Quorum sensing (QS) is a population-density dependent chemical process that enables bacteria to communicate based on the production, secretion and sensing of small inducer molecules. While recombinant constructs have been widely used to decipher the molecular details of QS, how those findings translate to natural QS systems has remained an open question. Here, we compare the activation of natural and synthetic Pseudomonas aeruginosa LasI/R QS systems in bacteria exposed to quiescent conditions and controlled flows. Quantification of QS-dependent GFP expression in suspended cultures and in surface-attached microcolonies revealed that QS onset in both systems was similar under quiescent conditions but markedly differed under flow. Moderate flow (Pe > 25) was sufficient to suppress LasI/R QS recombinantly expressed in Escherichia coli, whereas only high flow (Pe > 102) suppressed QS in wild-type P. aeruginosa. We suggest that this difference stems from the differential production of extracellular matrix and that the matrix confers resilience against moderate flow to QS in wild-type organisms. These results suggest that the expression of a biofilm matrix extends the environmental conditions under which QS-based cell-cell communication is effective and that findings from synthetic QS circuits cannot be directly translated to natural systems.
Highlights
Quorum sensing (QS) is a population-density dependent chemical process that enables bacteria to communicate based on the production, secretion and sensing of small inducer molecules
LasI synthesizes acyl-homoserine lactone (HSL) inducer molecules that are released into the surrounding fluid and – according to the classic quorum sensing (QS) model developed for quiescent environments – the local HSL concentration increases with increasing bacterial population density[4]
E. coli strains were grown overnight on lysogeny broth (LB) agar plates in the absence of ambient flow and colonies were analyzed by epifluorescence microscopy. 98% of E. coli quorum sensing reporter construct (QSR) expressed GFP while no fluorescence was detected for E. coli CTRL cells, confirming functionality of the engineered QS constructs (Fig. 2A,B)
Summary
Quorum sensing (QS) is a population-density dependent chemical process that enables bacteria to communicate based on the production, secretion and sensing of small inducer molecules. We suggest that this difference stems from the differential production of extracellular matrix and that the matrix confers resilience against moderate flow to QS in wild-type organisms These results suggest that the expression of a biofilm matrix extends the environmental conditions under which QS-based cell-cell communication is effective and that findings from synthetic QS circuits cannot be directly translated to natural systems. To reduce the system complexity and afford greater experimental control, natural QS systems are frequently isolated from the host and expressed recombinantly, often in Escherichia coli, using synthetic biology approaches[9,10,11] This has yielded significant insights into the behavioral consequences and molecular details of QS. Mathematical models further revealed that flow above a biofilm can switch the QS response in biofilms suggesting that the quorum sensor acts as a flow sensor[25] and that QS activation of bacterial colonies is substantially delayed with flow[26]
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