Assessment of Bioactive Potential and Characterization of an Anticancer Compound from the Endophytic Fungi of Ocimum sanctum

Abstract

The goal of this study was to isolate endophytic fungi from Ocimum sanctum L. and to evaluate their biological potential, including antibacterial, antioxidant, and enzymatic activities and further characterization of the bioactive compounds. Nine endophytic fungi were isolated from the leaves and stem tissues of O. sanctum collected from the botanical garden of Banaras Hindu University, Varanasi, India. All isolates were identified based on their microscopic structures and molecular sequencing of the ITS rDNA. Aspergillus clavatonanicus (SS7) and Cochliobolus hawaiiensis (SL3) showed the highest colonization frequencies in the stem and leaves (16 and 14%, respectively). All fungal isolates were tested for extracellular enzymatic activities of amylase, cellulase, and pectinase. Of the nine fungal isolates, 60% tested positive for amylase and cellulase, whereas 50% showed pectinase activity. Using a disc diffusion assay, the extracted secondary metabolites were checked for antibacterial activity against three human pathogenic bacteria. Two isolates, SL2 and SS7, exhibited the highest antibacterial activity against all pathogens, including Enterococcus faecalis, Klebsiella pneumoniae, and methicillin-resistant Staphylococcus aureus (MRSA). Crude extracts of the six fungal isolates showed positive antioxidant activity. The crude extract of Aspergillus allahabadii (isolate SL2) showed strong antibacterial and antioxidant activities and crystallized during purification. X-ray crystallography confirmed the identity of the crystal as citrinin, which also exhibited strong anticancer activity against Dalton’s lymphoma cells. The results of this study suggest that endophytic fungi isolated from the leaf and stem tissues of Ocimum sanctum are potential sources of antibacterial, antioxidant, and anticancer compounds.