Fungal endophytes: isolation, identification and assessment of bioactive potential of their natural products.
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Date
2017
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Abstract
Fungal endophytes produce a broad variety of bioactive compounds with potential to address
some of the unmet human needs. Medicinal plants have an important role to play in the search for
new strains of endophytes fungi, as it is possible that their beneficial characteristics are as a result
of the metabolites produced by their endophytic community. However, inspite of this potential as
repositories of bioactive compounds, the fungal endophytes of African medicinal plants remain
largely underexplored. This thesis reports on studies that were conducted to bioprospect for
endophytic fungi with antioxidant and antimicrobial activity hosted by the plants Warburgia
salutaris, Annona senegalensis, Kigelia africana and Vitex payos used in Zimbabwean traditional
medicine. The surface sterilization technique was used to isolate the endophytic fungi that were
identified by ribosomal DNA sequencing of the nuclear ribosomal internal transcribed spacer
region. Crude extracts obtained from the fermentation of the isolated endophytic fungi were
screened for antimicrobial activity using the agar diffusion method and evaluated for total
antioxidant activity using a commercial kit that used the single electron transfer mechanism.
Fourier-transform infrared spectroscopy (FT-IR) and Gas Chromatography – Mass Spectrometry
(GC-MS) were used to provide a snapshot of the metabolites present in the endophyte fungi
extracts. A total of 33 endophytic fungi were isolated from the medicinal plants and the fungal
endophyte colonisation rates varied by plant species and plant tissue. The isolated fungi across
the different plant species and tissue types were found to be dominated by members of the phylum
Ascomycota. The endophytic fungi Penicillium chloroleucon was isolated from all the plant
species except for Cladosporium uredinicola and Myrothecium gramineum (both isolated from
Kigelia africana) which had an inhibitory effect against Escherichia coli (ATCC1056). Whilst
Epicoccum sorghinum isolated from Annona senegalensis exhibited the most potent antioxidant
activity, a significant number of the screened endophytic fungi from the different plant species
were also found to have some antioxidant activity. The total phenolic content was found to have
a positive correlational relationship with total antioxidant activity of the screened endophytic
fungi crude extracts. The endophytic fungi were shown to produce a diverse range of metabolites
including phenolic and polyphenolic compounds through FT-IR and GC-MS analysis. The isolate
Cladosporium uredinicola has potential as a source of antimicrobial compounds whilst the isolate
Epicoccum sorghinum has potential as a source of natural antioxidant. Antioxidant activity is a
common phenomenon in the studied endophytic fungi and the fungal endophytes of the medicinal
plants of Zimbabwe have potential as sources of bioactive compounds.
Keywords: Bioprospecting, antioxidant, antimicrobial, endophytic fungi, medicinal plants,
Zimbabwe.
Description
Doctoral Degrees. University of KwaZulu-Natal, Durban.