Abstract
Endophytic and rhizosphere fungi are understood to be aiding the host plant to overcome a range of biotic and abiotic stresses (nutrition depletion, droughts, etc.) hence, they remain to be reservoirs of plethora of natural products with immense use. Consequently, this investigation of endophytic and rhizosphere fungi isolated from Mikania cordata (a perennial vine that is well established in Sri Lanka) for their antimicrobial properties was performed with the aim of future derivation of potential beneficial pharmaceutical products. Leaves, twigs, and roots of M. cordata were utilized to isolate a total of 9 endophytic fungi out of which the highest amount (44%) accounted was from the twigs. A sample of the immediate layer of soil adhering to the root of M. cordata was utilized to isolate 15 rhizosphere fungi. Fusarium equiseti and Phoma medicaginis were endophytes that were identified based on colony and molecular characteristics. The broad spectrum of antimicrobial activity depicted by F. equiseti (MK517551) was found to be significantly greater (p ≤ 0.05, inhibitory against Bacillus cereus ATCC 11778, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 25853) than P. medicaginis (MK517550) (inhibitory against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 25853) as assessed using the Kirby-Bauer disk diffusion method. Trichoderma virens and Trichoderma asperellum were rhizospere fungi that exhibited remarkable antimicrobial properties against the test pathogens chosen for the study. T. asperellum indicated significantly greater bioactivity against all four bacterial pathogens and Candida albicans ATCC 10231 under study. The ranges of minimum inhibitory concentrations (MICs) of the fungi depicting antimicrobial properties were determined. The results obtained suggest that F. equiseti, P. medicaginis, T. asperellum, and T. virens of M. cordata harness bioprospective values as natural drug candidates. This is the first report on isolation and evaluation of the antimicrobial properties of endophytic and rhizosphere fungi of Mikania cordata.
Highlights
The exacerbation of drug resistance towards numerous commercially available antibiotics by many existing pathogenic fungi and bacteria has piqued the discovery of novel therapeutics rather important and timely
The absence of epiphytes or surface-adhering microorganisms was confirmed from the tissue imprint procedure which indicates that the surface disinfection was complete
Effectiveness of surface disinfection could be reassured by culturing aliquots of water from the final washing step on Potato Dextrose Agar (PDA) enriched with antibiotics [24]
Summary
The exacerbation of drug resistance towards numerous commercially available antibiotics by many existing pathogenic fungi and bacteria has piqued the discovery of novel therapeutics rather important and timely. Inappropriate prescription, lack of new antibiotics, and regulatory barriers for research play a hand in increasing resistance. Endophytic and rhizosphere fungal microbiota are found to contain a high metabolic capability in terms of producing a myriad of secondary metabolic products (peptaibols, diketopiperazines, sesquiterpenes, steroids, etc.) which can be exploited as antimicrobials, anti-inflammatory agents, antitumour agents, antioxidants, and even plant growthpromoting agents [4]. The quantities and types of secondary metabolites produced by the fungi residing in plant tissues and those found in the plant’s rhizospheric soils could depend on a cluster of biotic and abiotic factors such as the microbiome-host interactions, humidity, environmental temperature, type of soil, and quality of root exudates [5]
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