Induction of toluene degradation and growth promotion in corn and wheat by horizontal gene transfer within endophytic bacteria

Some experiments involving important crop plants, corn and wheat, were carried out to characterize the agronomic and environmental application of Burkholderia cepacia strain FX2 able to degrade toluene and containing plasmids with the gene encoding for catechol 2, 3-dioxygenase (C23O), a key enzyme in the degradation pathway of monocyclic aromatic compounds. The inoculation of corn and wheat with FX2 led to the promotion of plant growth and reduction in evapotranspiration of toluene into the air. Endophytic bacteria able to grow on toluene as the only source of carbon and containing a C23O gene were found in the plants inoculated with FX2 but not in their non-inoculated controls. Compared to control plants, a greater number of toluene-degrading, phosphate-solubilizing and siderophore-producing endophytes were found in inoculated plants. Furthermore, a direct correlation occurred between plant biomass responses and the magnitude of C23O-containing endophytes. Phylogenetic tree comparison, plasmid analysis and filter mating assays showed that the C23O gene was transferred horizontally from FX2 to the natural endophytic bacteria of corn and wheat. Horizontal gene transfer among endophytic bacteria might contribute to pollutant degradation, growth promotion and potential for disease suppression in corn and wheat.