The slow growth of the Xylella fastidiosa bacterium: metabolic accident or epidemic strategy?

Xylella fastidiosa infects several plants such as vines, citrus fruits, almond or olive trees. Different strains of the subspecies multiplex are present in Corsica on many plants of the scrubland. It is also present in the Provence Alpes Côte d'Azur region with the subspecies: pauca. Very recently, the multiplex subspecies was detected in the Aude department, on a lavandin plant.

How is this expansion and virulence possible when this pathogen has a very slow growth that is described as fastidious?

So slow that it complicates its diagnosis in plants and its study in laboratories. This physiological characteristic, shared with several human pathogenic bacteria, seems paradoxical. Yet, this slow growth is an intrinsic characteristic of the organism. A research team from the Laboratoire des Interactions Plantes Microbes Environnement (INRAE-CNRS) and researchers from the Institut de Recherche en Horticulture et Semences (INRAE) in Angers, France, have worked together to better understand the metabolism of this bacterium.

Using systems biology and modeling tools, the researchers discovered that the metabolic network of Xylella fastidiosa is, against all expectations, complete but reduced to the essential. It contains, for example, half as many reactions as the reference organism Escherichia Coli. As a result, redundant metabolic pathways have disappeared, especially those that promote rapid and efficient growth. The metabolic network of Xylella fastidiosa is therefore inefficient and fragile. The synthesis of exopolysaccharide, one of its virulence factors, has also been shown to be inefficient and even becomes a burden for growth.

A weakness that becomes a strength

It seems that this fastidious growth is the result of an evolution of this pathogen, probably allowing it to escape detection by the plant immune system and hence defense mechanisms. A strategy that seems to be winning, considering the increasing spread of Xylella fastidiosa in the world.

To gain further insight into the metabolism of Xylella fastidiosa, studies of several genes have begun in order to better understand their involvement in the fastidious growth observed.

Scientists are also seeking to better understand how this slow growth affects the spread of the bacterium in host plants. All these advances are necessary to better control the bacterium.