Due to the relationships that endophytes seem to have with their host plants, they make a myriad of biologically active compounds. These compounds can be classified as antibiotics, antioxidants, anticancer agents, volatile antimicrobial agents, immunosuppressive compounds, plant growth promoting agents, and insecticides (1). It has been reported that endophytes possess the ability to produce the same or similar chemicals as those originating from their host plants (2, 3). This presents endophytic microorganisms as potential alternatives to plants in the search for biologically active molecules.
Various scientific studies have shown that
In our search for biologically active molecules from endophytic fungi associated with Nigerian plants, this present study was carried out to investigate the secondary metabolites of endophytic fungi isolated from three Nigerian medicinal plants
Fresh leaves of
Preliminary antimicrobial screening of the endophytic fungal extracts was carried out using the agar well diffusion assay method as described by Akpotu
HPLC analysis was carried on the fungal extracts was carried out as described by Eze
Result of antimicrobial assay of endophytic fungal extracts showing the inhibition zone diameters (IZDs) produced against test isolates
IZDs (mm) | |||||||
---|---|---|---|---|---|---|---|
Test Organisms | NL-L1 | NL-L2 | SL-L1 | PPL-LAC | PPL-LE2 | Positive control Gentamicin (10 μg/ml) | Negative control DMSO |
0 | 9 | 7 | 3 | 4 | 17 | 0 | |
0 | 0 | 5 | 0 | 3 | 21 | 0 | |
0 | 6 | 6 | 0 | 0 | 22 | 0 | |
0 | 6 | 8 | 0 | 0 | 16 | 0 | |
Ketoconazole (50 μg/ml) | DMSO | ||||||
0 | 0 | 0 | 0 | 0 | 17 | 0 | |
0 | 0 | 0 | 0 | 0 | 4 | 0 |
A total of five endophytic fungi was isolated, two from
Biological activities/applications of detected compounds
Plants | Endophytic fungi | Compounds detected by HPLC analysis | Biological activities/applications | References |
---|---|---|---|---|
NL-L1 | Ethyl 4-hydroxyphenyl acetate | An intermediate for the preparation of anti-inflammatory agents | (42) | |
Ferulic acid | Antioxidant anti-diabetic, antihypertensive, anticancer, anti-inflammatory, hepatoprotective, antimicrobial, anti-allergic, increase sperm viability, antithrombotic, antiviral and vasodilatory actions, metal chelation, modulation of enzyme activity, activation of transcriptional factors, gene expression and signal transduction activities | (43-54) | ||
NL-L2 | Ruspolinone | Organocatalysts and building blocks in organic synthesis | (55,56) | |
SL-L1 | Protocatechuic acid | Antioxidant, antimicrobial, anticancer, anti-ulcer, antidiabetic, anti-ageing, antifibrotic antiviral, anti-inflammatory, analgesic activity, anti-atherosclerotic, cardiac, hepatoprotective, neurological and nephroprotective activities | (57-71) | |
Cladosporin | Antiplasmodial, antimicrobial, insecticidal, and antitumor activities | (72-76) | ||
Scytalone | Plant growth promotion, intermediate in the biosynthesis of melanin in fungi | (77-80) | ||
PPL-LAC PPL-LE2 | Indole-3-acetic acid Indole-3-acetic acid | Cytotoxic/anticancer, antioxidant, anti-inflammatory activities | (81-83) | |
Indole-3-carbaldehyde | Cytotoxic and antibacterial activities, associated with the innate immunity to microbial pathogen infections in plants | (84-86) |
The antibacterial activity displayed by the endophytic fungal extracts can be attributed to the antimicrobial compounds present in the extracts. As can be observed in Table 2, compounds with antimicrobial properties detected by HPLC analysis of the fungal extracts include: ferulic acid, cladosporin, indole-3-carbaldehyde, and protocatechuic acid. The other detected compounds (ethyl 4-hydroxyphenyl acetate, ruspolinone, scytalone, and indole-3-acetic acid) possess diverse biological activities that include cytotoxic/anticancer, antioxidant, anti-inflammatory activities, etc. (42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86).
Ferulic acid, a derivative of cinnamic acid, is a predominant natural phenolic compound first isolated from the plant
Protocatechuic acid (3,4-dihydroxybenzoic acid) is a widely distributed naturally occurring phenolic acid present in most edible and medicinal plants (53, 90, 91, 92). The compound has also been reported to be produced by several species of bacteria and fungi (40, 57, 93, 94, 95). Protocatechuic acid has been reported to show antioxidant, antimicrobial, anticancer, anti-ulcer, antidiabetic, anti-ageing, antifibrotic antiviral, anti-inflammatory, analgesic activity, anti-atherosclerotic, cardiac, hepatoprotective, neurological and nephroprotective activities (57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71).
Cladosporin is an isocoumarin derivative previously isolated from
Indole-3-carbaldehyde (indole-3-carboxaldehyde), an indole alkaloid, had been isolated from an endophytic
Indole-3-acetic acid is the most abundant and well known plant hormone of the auxin class which regulates various aspects of plant growth and development (99, 100, 101). Many bacterial and fungal species have been reported to be able to produce indole-3-acetic acid (40, 99, 101, 102). Indole-3-acetic acid has been reported to possess cytotoxic/anticancer, antioxidant, anti-inflammatory activities (81, 82, 83).
Ethyl-2-(4-hydroxyphenyl) acetate (ethyl
Ruspolinone, a pyrrolidine alkaloid, was isolated from the plant
Scytalone, a tetralone derivative, has been previously isolated from several endophytic fungi which include
Studies of the endophytic fungal population of Nigerian plants have revealed the potentials possessed by these plants as host to endophytes that express important biological active compounds (2, 3, 40, 41, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121). These endophytes also hold key of possibilities to the discovery of novel molecules for pharmaceutical, agricultural and applications.
Endophytic fungi isolated from with three Nigerian plants