Investigating endophytic fungi of Calotropis procera for novel bioactive compounds: molecular docking and bioactivity...

The rising danger of antibiotic resistance and the increasing burden of cancer worldwide have highlighted the necessity for a constant supply of new antimicrobial drugs and anticancer therapies. Endophytic fungi, recognized as a rich supplier of secondary metabolites with novel bioactivities that have shown promising antimicrobial and anticancer potential, were isolated from the medicinal plant Calotropis procera. Approximately 70 segments from the leaves and stems of the C. procera plant were evaluated for endophytic colonization, resulting in the isolation and identification of five fungal species based on morphological characteristics.

A total of five endophytic fungal species were isolated from Calotropis procera and identified, with Aspergillus versicolor exhibiting the highest frequency of occurrence (50%). In contrast, the remaining fungal species were found at a frequency of 25% each. The endophytic fungal filtrates were evaluated for antimicrobial efficacy against seven pathogens, demonstrating significant inhibition zones ranging from 7 to 25 mm. Additionally, the anticancer activity was assessed against two cell lines, MCF-7 and HCT-16, with IC₅₀ ranging from 7.8 to 50.4 µg/mL. Among the isolates, the filtrate of Aspergillus niger (Accession number PQ568010) exhibited the highest antimicrobial and anticancer activities. The crude extract of A. niger was developed to identify the chemical constituents by gas chromatography. The most active component in the extract, as analyzed by ¹H NMR, revealed that 2,2,4,4-tetramethylpentane was the primary compound responsible for these effects, which demonstrated significant inhibitory activity against Staphylococcus aureus and Bacillus cereus, with inhibition zones of 23 mm and 20 mm, respectively. Molecular docking studies were performed against Phenylalanine-tRNA ligase alpha subunit of Bacillus cereus (UniProt ID: Q633N4), GTPase Der of Escherichia coli (UniProt ID: P0A6P5), peptidoglycan-N-acetylglucosamine deacetylase of Listeria monocytogenes (UniProt ID: A0A3Q0NBH7), DNA gyrase subunit B of Salmonella typhimurium (UniProt ID: P0A2I3), Zinc metalloproteinase aureolysin of Staphylococcus aureus (UniProt ID: P81177), Agglutinin-like protein 2 of Candida albicans (UniProt ID: Q9URQ0), serine/threonine-protein kinase of Saccharomyces cerevisiae (UniProt ID: P32600).

The study highlights the potential of endophytic fungi Aspergillus niger as a promising source of novel antimicrobial and anticancer agents. The identification of 2,2,4,4-tetramethylpentane as the primary bioactive compound, combined with the molecular docking analyses, provides valuable insights into the mechanisms of action and potential therapeutic applications. These findings underscore the importance of exploring endophytic fungi for the development of new drugs to combat antibiotic resistance and cancer.