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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #303041

Title: A Mathematical model to investigate quorum sensing regulation and its heterogenecity in pseudomonas syringae on leaves

item PEREZ-VELAZQUEZ, JUDITH - Helmholtz Centre
item Quinones, Beatriz
item HENSE, BURKHARD - Helmholtz Centre
item KUTLER, CHRISTINA - Technical University Of Munich

Submitted to: Ecological Complexity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2014
Publication Date: 3/1/2015
Publication URL: http://dx.doi.org10.1016/j.ecocom.2014.12.003
Citation: Perez-Velazquez, J., Quinones, B., Hense, B., Kutler, C. 2015. Mathematical modelling of quorum sensing of pseudomonas syringae on leaves. Ecological Complexity. 21:128-141.

Interpretive Summary: Bacteria produce and sense small diffusible signal molecules called autoinducers thru a process known as quorum sensing (QS). When bacterial cell numbers increase to reach a quorum, this process leads to the regulation of a variety of genes in a density-dependent manner. The QS-regulated genes include virulence, biofilm formation, colonization of host surfaces, extracellular polysaccharide production, motility, and other bacterial processes. Although the term “quorum sensing” makes a direct reference to population size, it is now widely accepted that other factors such as characteristics of the environment could influence the QS regulation system. QS has usually been studied in environments where signal concentrations accumulate to sufficiently high levels to induce QS. In this paper, through mathematical modelling, we investigate QS in a non-water-saturated environment, the phyllosphere (leaf surfaces). Studying QS in environmental systems is complex since bacteria rarely encounter conditions similar to a well-mixed planktonic culture. The physical, biological, and chemical conditions of the surrounding environment have the potential to influence QS. Recent evidence stated that the hydrodynamic environment can impact QS in a biofilm. The amount of biofilm biomass required for full QS induction of the population increased as the flow rate increased. It is believed that autoinducer regulation networks may generate spatially heterogeneous behavior with a special focus on the influence of nutrients as an example for interacting environmental factors. Based on experimental observations, the present study has explored QS in the plant pathogenic bacterium Pseudomonas syringae. A mathematical model of QS, based on computing the integral of a non-negative stochastic process, is presented where the stochastic process comes from a population growth dynamics model. We focus on exploring how water availability and diffusional loss of autoinducers affect the process of QS induction. Our results indicated that water availability impact QS onset and affect autoinducers diffusion away from the producing cells.

Technical Abstract: The bacterium Pseudomonas syringae is a plant-pathogen, which through quorum sensing (QS), controls virulence. In this paper, by means of mathematical modeling, we investigate QS of this bacterium when living on leaf surfaces. We extend an existing stochastic model for the formation of Pseudomonas syringae’s colonies by computing the integral of a non-negative stochastic process and study the QS state of the colonies. We investigate the extent to which factors such as water availability and diffusional losses of QS signalling molecules (autoinducers) would affect QS across colonies. Our results support that QS activation is indeed a good indicator of diffusional limitation, as QS is enhanced when diffusion of autoinducers signal decreases (either as a result of water availability or loss by diffusion). Furthermore, we are able to test whether QS activation of this bacterium may be heterogeneous (cells do not activate homogeneously with the rest) when growing in their natural habitat. Stochastic growth and uneven nutrient availability of the leaf surface may contribute only partially to the heterogeneity observed.