Uncovering the mechanisms of bacteria with toxic superpowers

Since 2013, with a peak in 2024, a large part of olive oil production in Italy and southern Europe has been threatened by a bacterium, Xylella fastidiosa, responsible for the destruction of olive trees in southern Europe. Since 2013, the bacterium known as olive leprosy has already caused the death of a million trees in the Puglia region of Italy.

A team of scientists from UCLouvain, led by Claude Bragard, a researcher at the Earth and Life Institute, decided to study how a cousin of this bacterium, Xanthomonas translucens (responsible for bacterial stripe disease of wheat) attacks the plant. The aim? To gain a better understanding of its attack mechanisms so that they can be countered.

In concrete terms, this Xanthomonas bacterium is capable of invading the intercellular spaces in the leaves of cereals, where it develops to the detriment of the plant. Another finding is that it does not live alone on and in the plant, but also has to contend with other bacteria competing for resources, with which it is engaged in a veritable war. To win the battle, this bacterium has developed a series of mechanisms that enable it to kill or inactivate other bacteria sharing the same environment.

The UCLouvain study focused on two antibacterial weapons, namely secretion systems or structures comparable to “molecular syringes”, with which the bacterium is able to inject toxic molecules into enemy bacterial cells capable of killing them, known as effector molecules. The study shows that within Xanthomonas translucens, there has undoubtedly been an evolution in the secretion system used by the bacterium.

Scientists at UCLouvain have developed a tool for visualising these interactions in real time using genetically modified fluorescent bacteria and confocal microscopy videos. Initially tested on Escherichia coli, this model can also be applied to bacteria naturally present in the wheat microbiome. This major discovery has been published in the prestigious scientific journal Nature Ecology & Evolution.

Exploring these mechanisms of competition between bacteria offers new prospects for combating this pathogen, while preserving the plant's beneficial microbiome. By way of comparison, this discovery is of the same importance as when scientists discovered the impact of the intestinal microbiota on our health.

This article was originally written in French by the AREC team of UCLouvain. It is available to be read here.

Communication of these research results resulted in significant press coverage, notably in La Libre and L'Avenir.