Antibacterial mechanisms of methyl gallate against Ralstonia solanacearum

Methyl gallate (MG) strongly inhibited effect on the plant-pathogenic bacterium Ralstonia solanacearum. Observations using a scanning electron microscope showed damage by MG to the cell wall structure of the pathogen, morphological changes and plasmoptysis. The results of biochemical analysis showed that MG exhibited substantial inhibitory effects on the protein synthesis and succinate dehydrogenase (SDH) activity in the pathogen. After treatment with 20 mu g/mL MG, R. solanacearum could counteract the inhibition of MG and regain its growth via stress responses such as elevated Na+K+-ATPase activity and production of a large quantity of exopolysaccharides. However, the pathogen lost its pathogenicity, which can be attributed to suppression of extracellular enzymes such as pectinase and cellulase. Moreover, MG at higher concentrations exhibited its bactericidal effect by inhibiting the respiration of bacteria which in-turn interferes their energy metabolism.