Abstract Description

Fungal endophytes produce structurally and chemically diverse compounds such as terpenoid, flavonoids, saponins, steroids and alkaloids with compounds antimicrobial, antioxidant, and anti-inflammatory activities. However, the potential of the fungal endophytes to produce xylitol remains largely underexplored. This study investigated the potential of fungal endophytes isolated from the South African medicinal plant, Monsonia angustifolia, to produce xylitol and assessed the antibacterial and antioxidant properties of their ethyl acetate crude extracts (CEs). A total of 21 endophytic filamentous fungi and 8 endophytic yeasts obtained from leaves, stems and spikes of M. angustifolia were screened for their xylitol production potential using xylose fermentation media (XFM). Xylitol production was determined after 24, 48 and 72 h of fermentation and quantified using high-Performance liquid chromatography (HPLC). The cell-free fermented broths of the isolates with the highest and lowest xylitol production from each tissue were extracted with ethyl acetate. The CEs were screened for their antibacterial and antioxidant activity using broth micro-dilution and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays, respectively. The total phenolic content of the CEs was determined using the Follin-ciocalteu reagent assay. All the filamentous fungi demonstrated the ability to produce xylitol with concentrations ranging from 0.13–1.40 g/L, with Aspergillus aculeatus MaL-9 demonstrating the highest xylitol production after 72 h. Only 7 yeast endophytes were able to produce xylitol with concentrations ranging from 0.07–1.73 g/L, with Rhodotorula mucilaginosa MaST-16 having the highest xylitol production after 72 h. The minimum inhibitory concentrations (MIC) of the CEs ranged from 1.25–2.50 mg/mL against clinically significant bacterial pathogens for both the filamentous fungal and the yeast endophytes. The antioxidant activity was recorded as EC50, whereby Epicoccum thailandicum MaST-2 and had highest antioxidant activity of 2187±5.7 µg/mL, with highest total phenolic contents (TPC) of 14.98±0.24 mg GAE/g extract. The yeast endophyte Rhodotorula mucilaginosa MaST-16 had the highest antioxidant activity of 7483±5.3 µg/mL, with highest TPC of 14.98±0.24 mg GAE/g extract. This study demonstrated that highly diverse fungal endophytes of M. angustifolia are potential sources of xylitol and phenolic compounds with antimicrobial and antioxidant activity.