Antimicrobial activity of Diisooctyl phthalate fraction from endophytic fungusHypoxylon griseobrunneum isolated from Thunbergia fragrans

Abstract

The present study investigated the isolation, characterization, and antimicrobial potential of endophytic fungi from the medicinal plant Thunbergia fragrans. Six fungal isolates were obtained from surface-sterilized stems and leaves. Among these, isolated TF3 demonstrated the strongest antimicrobial activity. Ethyl acetate extract of TF3 showed significant inhibition against Bacillus subtilis, Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli with inhibition zones ranging from 20 ± 0.54 to 23 ± 0.89 mm, occasionally exceeding those of gentamicin. Minimum inhibitory concentration (MIC) values ranged from 5 to 10 mg/ml, with E. coli showing the lowest MIC (5 ± 0.18 mg/ml). The extract also exhibited antifungal activity against C. albicans (12 ± 0.31 mm), Aspergillus fumigatus (11 ± 0.28 mm), Fusarium oxysporum (10 ± 0.22 mm) and Penicillium chrysogenum (10 ± 0.17 mm), with MIC and minimum fungicidal concentrations (MFC) of 10 mg/ml. Molecular identification via ITS rDNA sequencing identified TF3 as Hypoxylon griseobrunneum (GenBank accession: PP794700). Column chromatography was used to partially purify the methanol fraction, which was analyzed by GC-MS, revealing six major compounds, predominantly diisooctyl phthalate (DIOP). The structure of DIOP was further confirmed by FT-IR and ¹H-NMR spectroscopy. This is the first report of antimicrobial activity from a partially purified fraction containing DIOP from H. griseobrunneum isolated from T. fragrans. The findings underscore the potential of endophytic fungi from medicinal plants as promising sources of natural antimicrobialagents.