A mathematical model to investigate quorum sensing regulation and its heterogeneity in Pseudomonas syringae on leaves

Pseudomonas syringae is a plant-pathogen which, through the signalling system quorum sensing (QS), controls virulence. In this paper, we use the integral of a non-negative stochastic process to study the QS state of the bacterial colonies it forms when living on leaf surfaces. 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). Using further experimental data, we explore heterogeneity of QS activation of this bacterium (colonies do not become homogeneously activated) when growing in this natural habitat. We extend our model to test a hypothesis regarding the initial QS potential of the cells. We are able to conclude that stochastic growth and uneven nutrient availability of the leaf surface may contribute only partially to the heterogeneity observed. We discuss the possible (evolutionary) explanations of this strategy. (C) 2014 Elsevier B.V. All rights reserved.