Antibacterial cytochalasin B from endophytic Curvularia lunata isolated from Cyperus iria of Sri Lanka

Abstract

Antibiotic resistivity of bacteria has been increasing rapidly over the last few decades and currently it has become a severe human health crisis in the world. Therefore, isolating novel antibacterial drug leads from natural sources has become an essential requirement in today’s world. Thus, the main aim of the current study was to isolate the antibacterial compounds from the endophytic fungus Curvularia lunata isolated from an underutilized plant Cyperus iria of Sri Lanka. During a preliminary research C. lunata fungal extract showed antibacterial activity against Gram positive Staphylococcus aureus and Bacillus cereus. Hence the fungus was grown in large scale in 140 Petri dishes and was extracted to ethyl acetate after 21 days of incubation. The ethyl acetate crude extract (354 mg) obtained was purified using bioassay guided fractionations using a series of solvent/ solvent fractionations, Sephadex LH20 size exclusion chromatography using methanol as the eluent, normal phase silica gel chromatography using a gradient elusion and finally by reversed phase high performance liquid chromatography to isolate the major bioactive compound. The structure elucidation using 1H, 13C and 2D (COSY, HSQC, HMBC) nuclear magnetic resonance (NMR) and mass spectroscopic data revealed the identity of the major bioactive compound as cytochalasin B (1). Cytochalasin B showed prominent antibacterial activity with a minimum inhibitory concentration (MIC) of 64 μg/mL against S. aureus while the positive control Gentamycin showed a MIC of 4 μg/ mL. Further purification of other bioactive fractions with interesting 1H NMR spectra may to lead to novel antibacterial compounds. This study reveals that endophytic C. lunata of C. iria are potential producers of antibacterial compounds.