Whiteley and colleagues developed an experimental system to study signalling in Pseudomonas aeruginosa aggregates. They used a micro-3D-printing technique to enclose P. aeruginosa cells that produce a quorum-sensing signal in ‘traps’ of varying sizes. P. aeruginosa ‘responders’ (which respond to but do not produce the signal) that naturally formed aggregates in a synthetic cystic fibrosis sputum were then overlaid on top of the traps. Although aggregates containing ∼2,000 signal-producing P. aeruginosa cells displayed intra-aggregate signalling, they were unable to signal to neighbouring aggregates. By contrast, inter-aggregate signalling occurred when aggregates contained ≥5,000 cells. The distance from the trap also affected the number of responders, with fewer cells responding in the 121–180 μm range than in the 0–60 μm range. Finally, aggregates displayed differential sensitivity to the signal, and overexpression of the signal receptor in the responder strain resulted in increased sensitivity.
Darch, S. E. et al. Spatial determinants of quorum signaling in a Pseudomonas aeruginosa infection model. Proc. Natl Acad. Sci. USA https://doi.org/10.1073/pnas.1719317115 (2018)
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Du Toit, A. How to signal to your neighbours. Nat Rev Microbiol 16, 394 (2018). https://doi.org/10.1038/s41579-018-0026-z