Antimicrobial and Molecular Docking Studies of Anthrones from the Leaf Latex of Aloe pirottae A. Berger against Some Plant Pathogenic Microbes

Objective/Background: Aloe pirottae A. Berger has traditionally been used in Ethiopia to treat various ailments. While previous studies have examined the antimicrobial activity of different parts of A. pirottae against human pathogens, this study aimed to investigate whether its antimicrobial activity extends to plant pathogenic bacteria and fungi. Methods: Compounds were isolated from the leaf latex of A. pirottae using silica gel column chromatography, and their structures were determined using 1H-NMR, 13C-NMR, and ESI-MS spectral data. Both the leaf latex and the isolated compounds were evaluated for their antimicrobial activity against three bacterial ( Pseudomonas syringae pv. gaarcae, Ralstonia solanacearum and Xanthomonas vasicola pv. musacearum) and three fungal ( Fusarium graminarum, Fusaium oxysporum, and Fusarium solani) plant pathogens. Results: A mixture of two diastereoisomeric anthrones was isolated from the leaf latex of A. pirottae and characterized as aloin A/B using 1H-NMR, 13C-NMR, and ESI-MS. Aloin A/B showed the most potent activity against X. vasicola among the bacteria and F. oxysporum among the fungi strains tested, with minimum inhibitory concentrations (MIC) of 3.12 mg/mL and 6.25 mg/mL, respectively. Further exploration uncovered strong binding affinity of aloin A/B towards key proteins in these pathogens, specifically with topoisomerase II (−10.060 kcal/mol) and UDP-N-acetylmuramoyl-L-alanyl-D-glutamate-2, 6-diaminopimelate ligase (murE) (−8.861 kcal/mol) in F. oxysporum and X. vasicola, respectively, through molecular docking studies. Conclusion: The present findings highlight aloin A/B as promising natural antimicrobial agents and lead compounds for new plant pathogen treatments. Further research is recommended to explore their activity against a wider range of plant pathogens.