The potential of oxalate-degrading bacteria in plant protection

Henk-Jan Schoonbeek, Francesca Stefanato, Stephane Hess Carolina Buitrago, Eliane Abou Mansour and Jean-Pierre Métraux

Certain phytopathogenic fungi secrete oxalic acid as a pathogenicity factor. Some examples are the necrotrophic fungi Sclerotinia sclerotiorium and Botrytis cinerea. Several functions of oxalic acid in pathogen-host interaction have been proposed: (i) the secretion of oxalic acid lowers the pH on the plant surface that favours the action of pectolytic enzymes of the pathogen, (ii) oxalic acid blocks defence signal pathways in the plant, (iii) oxalic acid chelates bivalent ions in the middle lamella of cell walls, hence disrupting the plant tissue. Consequently, by degrading oxalic acid at the onset of host pathogen interaction, it should be possible to impede the infection process.
The aim of this project is to evaluate the possibility of using oxalate-degrading bacteria that colonize the plant surfaces and protect the plant from pathogen attack. We first isolated oxalate-degrading bacteria from the environment by enrichment on the rhizosphere of plants infected with Sclerotinia sclerotiorum (Fabio Mascher, currently at the Federal Agricultural Research station in Changins). Four of these Ox-strains, together with the biocontrol reference strain CHA0r, were used for protection assays in different pathosystems. Interesting results have been obtained against the oxalate-producing fungus Botrytis cinerea. We have observed that these 4 strains can protect tomato, cucumber and Arabidopsis against this pathogen. The strains do not produce significant amounts of antibiotics in vitro. The role of the oxalate-degrading ability is being tested on transposon-inserted mutants of Ox-strain Ralstonia campinenesis B that are unable to degrade oxalate in vitro.
This research includes:
  • Studies on the molecular determinants in the plant that are involved in the protective effect
  • Evaluation of the activity of Ox strains under field conditions
  • Possible improvements of the protective activity of Ox strains

This work recently attracted attention in the local newspaper "LaLiberté" (GO)