PRODUCTION OF HYDROXYBENZOIC ACIDS BY BRADYRHIZOBIUM-JAPONICUM STRAINS AFTER TREATMENT WITH GLYPHOSATE

Glyphosate [N-(phosphonomethyl)glycine] effects on the growth and metabolism of the nitrogen-fixing soybean (Glycine max) symbiont Bradyrhizobium japonicum were investigated. In higher plants glyphosate inhibits the shikimic acid pathway, causing accumulations of shikimic acid and certain benzoic acids, such as protocatechuic (PCA) and gallic acid. We sought to determine whether glyphosate also causes the accumulation of shikimic acid-derived benzoic acids in B. japonicum. Three strains (USDA 110, 123, and 138) were grown in defined media lacking aromatic amino acids. Glyphosate at concentrations of 0.5 and 1 mM was inhibitory but not lethal. Cell death occurred in response to 5 mM glyphosate, and rapid death was observed at 10 mM. Accumulations of 1 mM PCA were observed in the culture media of strains 123 and 138. Only trace amounts of PCA accumulated in untreated controls or in strain 110 cultures. All strains were able to metabolize PCA in the absence of glyphosate. The high levels of PCA produced by B. japonicum strains may alter the symbiotic interactions between this bacterium and glyphosate-resistant varieties of soybean.