Control of Acidovorax citrulli by the Antagonistic Bacterium Bacillus amyloliquefaciens and Pectate Lyase Inhibitory Properties of Bioactive Compounds by Molecular Docking

Pesticides that pose a risk to food safety can bioaccumulate in the human body and have many harmful effects with long-term exposure. The use of friendly microorganisms for plant health is a new approach to reducing pesticide use. Acidovorax citrulli, the causal agent of fruit blotch disease in watermelons and melons, poses a serious threat. In this study, the in vitro biocontrol of A. citrulli, which causes yield and quality losses, was investigated using bacterial strains isolated from different sources. Also, bioactive compounds produced by bacterial strains with antibacterial activity were analyzed by LC-ESI-MS/MS, and their inhibitory activity against pectate lyase was theoretically calculated using molecular docking. As a result of the isolation study to obtain potentially antagonistic bacterial strains, 189 strains were isolated and identified by fatty acid methyl ester analysis and biochemical tests. At the same time, strains with proven antibacterial activity were identified by 16S rRNA sequencing. The largest in vitro inhibition zone (37.26 mm) was observed with the strain Bacillus amyloliquefaciens IT 14. In the qualitative analysis of the bioactive compounds produced, the antibiotics Iturin A (1043.3 m/z), C-15 Iturin A (1057.5 m/z), Surfactin A (1008.3 m/z), Surfactin B (1022.3 m/z), and Surfactin C (1036.3 m/z) were determined with support from the literature. According to the molecular docking results, surfactin C (-7.6 kcal/mol) and iturin A (-7.2 kcal/mol) had the highest binding energies to the pectate lyase enzyme. The results of this study show that it may be important to determine which strain molecule with demonstrated antibacterial activity against the pathogen inhibits A. citrulli and to establish a control strategy for the disease accordingly.