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

Authors

  • Antonio Trovato,

    1. CNISM and Department of Physics and Astronomy “Galileo Galilei”, Università di Padova, Padova, Italy
    2. Istituto Nazionale Fisica Nucleare (INFN), Padova, Italy
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  • Flavio Seno,

    1. CNISM and Department of Physics and Astronomy “Galileo Galilei”, Università di Padova, Padova, Italy
    2. Istituto Nazionale Fisica Nucleare (INFN), Padova, Italy
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  • Marina Zanardo,

    1. Department of Agronomy, Animals, Food, Natural Resources and Environment DAFNAE, Università di Padova, Legnaro (Padova), Italy
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  • Sara Alberghini,

    1. Department of Agronomy, Animals, Food, Natural Resources and Environment DAFNAE, Università di Padova, Legnaro (Padova), Italy
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  • Alessandra Tondello,

    1. Department of Agronomy, Animals, Food, Natural Resources and Environment DAFNAE, Università di Padova, Legnaro (Padova), Italy
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  • Andrea Squartini

    Corresponding author
    1. Department of Agronomy, Animals, Food, Natural Resources and Environment DAFNAE, Università di Padova, Legnaro (Padova), Italy
    • Correspondence: Andrea Squartini, Department of Agronomy, Animals, Food, Natural Resources and Environment DAFNAE, Università di Padova, Viale dell'Università 16, 35020, Legnaro (Padova) Italy. Tel.: +39 049 8272923; fax: +39 049 8272929; e-mail: squart@unipd.it

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Abstract

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.

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