A first accomplishment of the project was the development of a methodology to simulate in vitro PCB stress in the model plant Arabidopsis thaliana. Metabolomics-based investigations in organic compounds released by the root (i.e. root exudates) showed a differential pattern of exudation under control conditions and in presence of PCB, representing the signature of root exudates potentially stimulating PCB degradation pathways in rhizosphere bacteria. Indeed, by modulating the exudation profile, the plant modifies the environmental niches of the root system to make them more prone to attract, recruit and affect the PCB degrading metabolism of soil bacteria, the so-called “cry for help” mechanism. Some root exudate molecules showed to be able to influence microbial motility, enhancing the chemotaxis toward the root system, while others are able to enhance microbial growth. All these aspects showed that root exudation is a key process in remodelling plant-associated microbiome to ensure key ecosystem services in contaminated soil.
A bacterial biosensor was generated, to investigate by fluorescence confocal microscopy the colonization profile of degrading bacteria on the root system and locate the active sites of the root where the expression of the reporter fluorescent label, responding to root exudates involved in enhancing the bacteria degradative metabolism, occurred. Importantly, PCB degrading bacteria showed a specific colonization profile, with preferential sites of adhesion being the root hairs or the root tip. Furthermore, a time-course of the fluorescent reporter activation lead to follow the dynamics and topography of the root exudates-driven stimulation of the bacterial PCB degradation pathway. The project contributed to develop a methodological approach to perform micro-profiling of the physico-chemical parameters in the root micro-habitats affected by the change in root exudation induced by PCB, through application of two different microsensor technologies. Complex plant-microbe interactions occur within a spatial area of few millimetres, therefore the knowledge of the specific physico-chemical conditions occurring are important to drive information on the influence that they can have on plant physiology and bacterial metabolism.
SENSE results were disseminated to an academic and scientific audience through participation to conferences and the publication of a manuscript that elaborate the evidence published so far to propose that ‘cry-for-help’ hypothesis, initially described in plant-pathogens challenge, may be part of the adaptation strategy to ensure the holobiont fitness in polluted environments. Outreach activities were performed to increase the awareness in general public of the fundamental role played by plant-associated microbiome in sustaining ecosystem services in contaminated environments.
