Detection and Characterization of Antibacterial Siderophores Secreted by Endophytic Fungi from Cymbidium aloifolium

Endophytic fungi from orchid plants are reported to secrete secondary metabolites which include bioactive antimicrobial siderophores. In this study endophytic fungi capable of secreting siderophores were isolated from , a medicinal orchid plant. The isolated extracellular siderophores from orchidaceous fungi act as chelating agents forming soluble complexes with Fe . The 60% endophytic fungi of produced hydroxamate siderophore on CAS agar. The highest siderophore percentage was 57% in (CAL1), 49% in (CAR12), 46% in (CAR14) by CAS liquid assay. The optimum culture parameters for siderophore production were 30 °C, pH 6.5, maltose and ammonium nitrate and the highest resulting siderophore content was 73% in . The total protein content of solvent-purified siderophore increased four-fold compared with crude filtrate. The percent Fe scavenged was detected by atomic absorption spectra analysis and the highest scavenging value was 83% by . Thin layer chromatography of purified siderophore showed a wine-colored spot with R value of 0.54. HPLC peaks with R s of 10.5 and 12.5 min were obtained for iron-free and iron-bound siderophore, respectively. The iron-free siderophore revealed an exact mass-to-charge ratio ( / ) of 400.46 and iron-bound siderophore revealed a / of 453.35. The solvent-extracted siderophores inhibited the virulent plant pathogens , that causes bacterial wilt in groundnut and pv which causes bacterial blight disease in rice. Thus, bioactive siderophore-producing endophytic can be exploited in the form of formulations for development of resistance against other phytopathogens in crop plants.