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FEMS Microbiol Lett. 2014 Mar;352(2):198-203. doi: 10.1111/1574-6968.12394. Epub 2014 Feb 19.

Quorum vs. diffusion sensing: a quantitative analysis of the relevance of absorbing or reflecting boundaries.

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CNISM and Department of Physics and Astronomy "Galileo Galilei", Università di Padova, Padova, Italy; Istituto Nazionale Fisica Nucleare (INFN), Padova, Italy.


The consequences of the boundary conditions (signal reflecting vs. signal adsorbing) on bacterial intercellular communication were addressed by a combined physics and microbiology approach. A predictive biophysical model was devised that considered system size, diffusion from given points, signal molecule decay and boundary properties. The theoretical predictions were tested with two experimental agarose-gel-based set-ups for reflecting or absorbing boundaries. N-acyl homoserine lactone (AHL) concentration profiles were measured using the Agrobacterium tumefaciens NTL4 bioassay and found to agree with model predictions. The half-life of AHL was estimated to be 7 days. The absorbing vs. reflecting nature of the boundaries drastically changed AHL concentration profiles. The effect of a single nonreflecting boundary side was equivalent to a 100-fold lower cell concentration. Results suggest that the kinetics of signal accumulation vs. signal removal and their threshold-mediated phenotypic consequences are directly linked to the properties of biofilm boundaries, stressing the relevance of the diffusion sensing component in bacterial communication.


AHL; boundary conditions; diffusion kinetics; quorum sensing

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