Abstract Description

Fungal endophytes produce a wide range of bioactive secondary metabolites. However, the production of these compounds is influenced by factors such as growth media and incubation conditions. This study evaluated the effect of agitation on the yield, composition and antimicrobial activity of secondary metabolites produced by fungal endophytes previously isolated from Artemisia afra. Nine isolates were cultured on potato dextrose broth under static and shaking conditions (150 rpm). The mycochemical profiles of the ethyl acetate crude extracts were determined using thin-layer chromatography (TLC) and quantified using high performance liquid chromatography (HPLC). Antibacterial activity of the crude extracts was assessed using broth micro-dilution and TLC-bioautography assays to determine the minimum inhibitory concentrations (MICs) and detect the presence of antibacterial compounds in the extracts, respectively. Sequencing of the internal transcribed spacer (ITS) region identified the isolates as members of the phylum Ascomycota. Static cultivation generally produced higher crude extract yields. Slight variations in mycochemical profiles were observed, with polyphenols, polyketides and quinones detected. The crude extracts exhibited inhibitory activity, with MICs ranging from 1.25–2.5 mg/mL. The shaking crude extracts of Alternaria destruens AaL-7a and AaL-8 strains displayed bactericidal activity (MBC = 2.5 mg/mL) against Enterococcus faecalis and Klebsiella pneumoniae. TLC-bioautography confirmed the presence of inhibitory compounds against all pathogens except Staphylococcus aureus. This study highlights the strain-dependent effect of agitation on the yield and composition of secondary metabolites produced by fungal endophytes.