Abstract Description

Endophytic yeasts have the potential to produce a variety of secondary metabolites with pharmaceutical applications. However, yeast endophytes associated with South African medicinal plants remain underexplored. Furthermore, the influence of fermentation conditions on the production and bioactivity of secondary metabolites from yeast endophytes is yet to be investigated. This study assessed the impact of culture media on mycochemical profiles and antimicrobial activity of yeast endophytes previously isolated from Monsonia angustifolia. Four isolates, Rhodotorula mucilaginosa MaST-16, Lodderomyces elongisporus MaST-17, Papiliotrema terrestris MaST-19, and Aureobasidium pullulans MaST-22, were cultivated in potato dextrose broth (PDB), malt extract broth (MEB), and yeast malt broth (YM) under shaking conditions (150 rpm). Mycochemical profiles of ethyl acetate crude extracts were analysed using thin-layer chromatography (TLC) and antimicrobial activity was assessed using broth microdilution and TLC-bioautography assays. The crude extract yields ranged from 53 – 374 mg in PDB, 37 – 159 mg in MEB, and 38 – 91 mg in YM. TLC analysis revealed differences in the composition and intensity of the spots for the different extracts obtained from each culture medium. Crude extracts from PDB and YM exhibited bacteriostatic activity against Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae while MEB extracts lacked inhibitory activity. These findings demonstrate that culture medium composition significantly influences the biosynthesis and bioactivity of secondary metabolites from endophytic yeasts, highlighting the importance of media selection for optimising the production of bioactive compounds.