Analysis of Low Molecular Weight Compounds Produced by Indigenous Wood Decay Fungi

Abstract

Over the years, natural products have played a major role in the search for novel drugs or drug candidates. Secondary metabolites from nature especially those of fungal origin exhibit unique biological activities and research continue to meet the keen interests which have potential pharmaceutical value. Fungi constitute an important source of secondary metabolites such as penicillin. The present study analyzed the biological activities of a variety of compound mixtures from wood decay fungi. A total of 54 wood decay fungi (WDF) were collected, with majority obtained from the University of Ghana campus and its surroundings. The WDF were cultured in potato dextrose broth (PDB) for 48 days and the time course analysis of two selected WDF were also performed to determine the profile of specific bioactivities. Cultures were terminated and extracted with ethyl acetate at the end of the 48th day of culture. WDF extracts were analyzed spectrophotometrically at wavelengths between 200 nm and 900 nm which showed high absorption in the UV region of the spectrum. TLC analyses of the fungal extracts were done using EtOAc: CH3CN: PetEth (7:2:1) as the solvent system and different classes of compounds were detected on TLC plates sprayed with Anisaldehyde reagent. UV detection of compounds on TLC showed unique band pattern for the different WDF. Assays for biological activities of the fungal extracts were performed against S. aureus ATCC.2, E. coli NMIMR.3, C. albicans KBTH.2 and A. niger ATCC.2 using disc diffusion assay method. From the primary screening of antimicrobial activity, a total of 40 WDF extracts were found to exhibit some form antimicrobial activity towards the test organism. Out of total 40 that had an activity, 10 of the WDF extracts were found to have biological activity selectively (SG+) against Staphylococcus aureus ATCC.2, and 13 extracts were also found to have a broad spectrum antimicrobial activity (BSAB) against Staphylococcus aureus ATCC.2 and Escherichia coli NMIMR.3. The number of extracts that had selective antifungal (SAF) activity towards Candida albicans KBTH.2 was found to be 3. The number of WDF that exhibited a non selective antimicrobial (NSAM) activity towards the three test organisms, S. aureus ATCC.2, E. coli NMIMR.3and C. albicans KBTH.2 were recorded to be 11. The time course analysis showed that fungal metabolites are produced as early as the 7th day of culture, however cultures that were harvested between 22nd and the 48th day of culture produced potent bioactive components. . After the secondary screening of 27 WDF, inhibitory activity against only S. aureus ATCC.2 was found to be possessed by 9 refermented extracts. Inhibitory activity towards both Gram positive and Gram negative bacteria tested was found in 6 extracts. Four (4) refermented extracts also exhibited inhibition towards S. aureus ATCC.2 and C. albicans KBTH.2. A shift in antimicrobial activity was observed after the secondary screen. Sephadex LH-20 fractions of the selected WDF extracts showed the broad spectrum activities of the individual fractions. All the extracts (A4, E2, E9 and F3) that showed broad spectrum activities against a Gram + and Gram – bacteria had common fraction/s possessing the biological activities. In those extracts (B6 and B7) that inhibited a Gram + bacteria and a fungus, the biological activities were seen in different fractions.