Toxicity, Antibacterial, and Antioxidant Activities of Fungal Endophytes Colletotrichum and Nigrospora spp. Isolated from Uvaria grandiflora
Kin Israel R. Notarte1,2*§, Mark Kevin P. Devanadera1,3§, Anna Beatriz R. Mayor1§,
Mary Christine A. Cada1, Melissa H. Pecundo1,5, and Allan Patrick G. Macabeo1,4
1The Graduate School
2Faculty of Medicine and Surgery
3Department of Biochemistry, Faculty of Pharmacy
4Laboratory for Organic Reactivity, Discovery, and Synthesis,
Research Center for the Natural and Applied Sciences (RCNAS)
University of Santo Tomas (UST), España 1015 Manila, Philippines
5South China Botanical Garden, Guangzhou, Guangdong 510650 China
§These authors contributed equally to this paper
Endophytic fungi are less explored in terms of their pharmacological applications, thus screening their phytochemical constituents and biological activities is of interest. In this study, the endophytic fungi Nigrospora and Colletotrichum spp. were isolated from the leaves of Uvaria grandiflora. The identity of the endophytes was established by molecular analysis of their fungal intergenic spacer. Biological screening showed that the fungal endophytes were most active against methicillin-resistant Staphylococcus aureus (MRSA), with the ethyl acetate broth extract of Colletotrichum sp. showing the biggest zone of inhibition (ZOI) for MRSA at 19 mm. For antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae, the ethyl acetate broth extract of Nigrospora sp. elicited better antibacterial activity (ZOI > 11 mm). Antioxidant assessment using 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and superoxide scavenging assays showed that Nigrospora broth extract had the best free radical scavenging activity with an IC50 of 3.92 mg/mL. Meanwhile, the broth extract from Colletotrichum sp. showed the best reducing power (RP50 = 4.41 mg/mL) and superoxide scavenging activity (SC50 = 0.78 mg/mL). Using Artermia salina for toxicity screening, both fungi were toxic having an LD50 < 0.40 mg/mL. The culture broth extracts showed greater antibacterial, antioxidant, and cytotoxic activities compared to the mycelial extracts. Phytochemical screening of the broth extract revealed the presence of flavonoids, sterols, phenols, and terpenoids in both fungal extracts. Tannins and coumarins were specifically detected in Colletotrichum sp., while alkaloids and indole derivatives were detected only in the Nigrospora endophyte.
Natural products and their derivatives are clinically used to treat cancer, microbial infections, metabolic disorders, and degenerative diseases (Thomford et al. 2018). A number of these natural products are isolated from plants and microorganisms (Wright 2018). The Philippines, which is a megadiverse country, is teeming with numerous sources of natural products that remain to be explored. Among these terrestrial flora, Uvaria from the Annonaceae family is reported to possess novel phytochemicals with a wide range of pharmacological activities (Macabeo et al. 2012, 2014, 2017; Paragas et al. 2014). In particular, Uvaria grandiflora Roxb. ex Hornem. remains to be an understudied plant species with antibacterial, antioxidant, and antiprotozoal properties (Ankisetty et al. 2006, Bibak et al. 2012). Despite the potential pharmacological value of U. grandiflora, issues concerning plant biodiversity conservation remain a constraint in natural products research. Therefore, studying microbial endosymbionts within plants as alternative sources for bioactive compounds is of timely interest. These microorganisms are called endophytes that symbiotically thrive within the host plants without causing disease and can be alternative sources of bioactive chemical agents (Zhao et al. 2011). The pharmacological and industrial significance of endophytes was first demonstrated by the production of taxol (paclitaxel) by Metarhizium anisopliae, which is a fungal endosymbiont of the Taxus tree (Visalakchi and Muthumary 2010). Aside from taxol, other chemotherapeutic agents were isolated from fungal endophytes – including campthothecin, oxacillin, ampicillin, and huperzine A (Akiyama et al. 2001, Han and Rahman 2012, Nair and Padmavathy 2014). Interestingly, the endophytes associated with U. grandiflora have not yet been explored. Thus, it is the goal of our work to isolate these endophytes and screen . . . . read more
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