KILL XYLL

Abstract

KILL XYL is a cure against the disease caused by Xylella fastidiosa, a plant pathogene. Actually, no extensive cure exist against this disease that causes the loss of thousands of hectares of European crops. KILL XYL has the goal to detect the symptom of the disease, then use specific phage-likes particles in order to inject toxins into X. fastidiosa. Finally, with the help of fatty acid it quench the quorum sensing activity of the bacterium and with an enzyme it degrade the biofilm, which is the principal cause of plants death. To be specific to X. fastidiosa, KILL XYL use a specific phage like particle able to recognized the pili and some extracellular protein by which the bacterium can be identified in a background of millions.

Motivation

Xylella fastidiosa is a bacterium that infects the xylem tissues of a wide range of plants. This bacterium has been widespread in the Americas for many years and occurs also in Asia. The bacterium is associated with several diseases of crops of economic significance, and has a wide range of host plants comprising 312 species.

X. fastidiosa is transmitted from plant to plant by xylem sucking insects. The bacterium can persist in symptomless uncultivated plants, from which insects may acquire the bacterium and pass it to crops. Symptoms of disease are only observed when xylem vessels are highly colonized by the bacterium. The xylem transports water and soluble mineral, nutrients from the roots throughout the plant, and used to replace water lost during transpiration and photosynthesis. Xylem vessels are interconnected by bordered pits, which allow the passage of xylem sap, but block the passage of larger objects (such as bacterium) by a membrane.

The control of the movement of potential hosts and insect vectors and the eradication of infected material is considered the most effective method of limiting the spread of the disease in the European Union. But there is no method yet to cure the trees.

Distribution map of Xylella fastidiosa worldwide.

KILL XYL concept

At Aix-Marseille University we thought about a solution that enclose many aspect of the cure.

First, we wanted to improve the detection of the disease, to do so we wanted to use a NDVI camera that will help us to see if the plant do photosynthesis or not. If the plant is heavily affected by Xylella fastidiosa, it support a hydric stress that stop the photosynthesis.

Secondly, we want to get rid of the bacterium. Phages are natural predators of bacteria. They can also be used to transfect DNA into a bacterial cell. Phages has also the advantage of being specific to a strain and to be modulable. As we wanted to be eco-friendly, we create phage-likes particles, that aren't able to spread. Thus we have nanobots specific to Xylella fastidiosa, capable to inject toxic genes into the bacterium.

The main cause of the plants death, is the hydric stress induced by the accumulation of biofilm into the xylem vessels. To disrupt the biofilm we thought about different solutions. The first one is to stop the bacterium producing any extra poly-saccharide. This could be achieved by quenching the quorum sensing of the bacterium with the help of a little fatty acid called : 2-cis-decenoic acid. Secondly, we wanted to destroy the exo-polysaccharids. An enzyme coming from a bacteriophage could fulfill the use by the hydrolysis of polysaccharides.

Hence, KILL XYLL simply detects, disrupt and kill Xylella fastidiosa.

Module 1: Detection of the disease

Module 2 : Engineering bacteriophages

Bacteriophages play a special role in nanoscale cargo-delivery developments, because they can be regarded as naturally occurring nanomaterials. Viral nanoparticles (VNPs), in particular bacteriophages, are attractive options for cargo-delivery as they are biocompatible, biodegradable, and non-infectious to mammals.

Phage systems, like M13, have been employed in biotechnological applications, most prominently in the identification and maturation of medically-relevant binding molecules through phage display. The application of phages in materials and nanotechnology is mainly due to their nanoscale size and simple life cycles. We choose to use those application in our advantage in order to target Xylella fastidiosa and other pathogenic bacteria.

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Module 3 : Quorum sensing approach

Module 4 : Disrupting the biofilm