Medicinal Plants: the untapped source of bioactive peptides/proteins

Traditionally used indigenous seeds of medicinal plants viz Hygrophila auriculata, Abrus precatorius, Moringa oleifera, Croton tiglium, Withania somnifera and Psoralae corylifolia were evaluated for antifungal against Aspergillus niger, Mucor mucedo, Fusarium solani, Ganoderma lucidum and antibacterial against Bacillus subtilis, Pasturella multocida, Escherichia coli and Staphylococcus aureus. The seeds were extracted in potassium phosphate buffer (pH=7.0). The extracts of M. oleifera, C. tiglium, W. somnifera and P. corylifolia showed significantly high antimicrobial activity (disk diffusion method) against the selected strains. Further purification was performed by 80% (NH₄)₂SO_4, dialysis, gel filtration (sephadex G-100) and DEAE-cellulose chromatography. SDS-PAGE analysis revealed a broad spectrum antimicrobial 50 kDa protein from Croton tiglium and 14.4 kDa peptide from seeds of M. oleifera which have not been reported in the literature. The protein/peptide showed antifungal activity against Mucor mucedo, Aspergillus niger, Fusarium solani and Metarhizium aniscoplae and antibacterial activity against P. multocida, S. aureus, E. coli and B. subtilis (fluconazole and rifmpacin as positive control for antifungal and antibacterial respectively). Minimum inhibitory concentration for fungal and bacterial strains ranged (±SD) 13.5±1.5–31±3.44 and 10.2±1.15–19.5±2.5µg/mL, respectively. The crude seed proteins showed strong potential in the treatment of waste water, particularly in reduction of microbial load (95%). The seed extracts of W. somnifera, C. tiglium and H. auriculata were found to be arrestant and toxic to assorted workers of Microtermes obesi. Seed extracts of these plants also showed effects on behavior and physiology of Odontotermes obesus (Isoptera: Termitidae). The antimicrobial and antitermitic of these medicinal plants demonstrated their potent therapeutic ability which might be explored multifariously.

Acknowledgement: Higher Education Commission, Government of Pakistan for funding the grant for this project.