Characterization of foliar endophytic fungi from Centella asiatica (L.) Urban as a promising source of bioactive metabolites
Loading...
Date
2015-08
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Endophytic fungi are source of novel compounds and have a great capacity to produce diverse class of plant secondary metabolites. Bioprospecting endophytes have led to exciting possibilities to explore and utilize their potential. In the present study, 13 foliar endophytic fungi were isolated from young and mature leaves of Centella asiatica (L.) Urban in summer, rainy and winter seasons. Out of 13 foliar endophytic fungi, 8 fungal isolates were morphologically identified as Colletotrichum gloeosporioides, Colletotrichum sp., Fusarium
sp., Curvularia sp., Nigrospora sp., Alternaria sp., Aspergillus sp. and Fusarium equiseti and
were studied further. Among all the fungal isolates, the isolation frequency of C. gloeosporioides was highest i.e. 24.14%. The qualitative screening of phytochemical constituents of ethyl acetate extract of fungal isolates revealed the presence of phenols, flavonoids, tannins, steroids, saponins, terpenoids, proteins, alkaloids, fats and carbohydrates.
The different fungal isolates exhibited varied antioxidant potential amongst which C.gloeosporioides exhibited highest antioxidant activity. The maximum phenolic and flavonoid content was also found in C. gloeosporioides. A positive correlation was found between the total phenolic content (r=0.98) and total flavonoid content (r=0.86) with DPPH scavenging ability. In antimicrobial assay, all the fungal extracts showed 100% inhibition against Bacillus subtilis, 75% against Escherichia coli and 62% against Pseudomonas aeruginosa and Staphylococcus aureus. The endophytic fungal isolates were also screened for extracellular enzymes production where 62 % of endophytic fungi showed positive results for lipase, 87% for amylase, 37% for both laccase and protease and none for cellulase. Further, the endophytic fungal extracts were screened for the presence of asiaticoside by LC-MS analysis. The asiaticoside producing fungal endophyte was identified as C. gloeosporioides by ITS ¼ sequencing. C. gloeosporioides was found to produce a maximum of 62.29 μg/100mL asiaticoside in PDB medium at 15th day of incubation. In the present study it was found that production of asiaticoside by C. gloeosporioides constantly decreased from first subculture generation to seventh subculture generation. C. asiatica plants were raised in vitro for cocultivation with C. gloeosporioides. Improved growth parameters were observed in cocultivated plants compared with control plants. The cocultivated plants have higher amount of phenolics, flavonoids, DPPH free radical scavenging activity and plant defense enzymes (SOD, POX, CAT, PAL and TAL) as compared to control. The asiaticoside content was also enhanced in cocultivated plants (4.08mg/g) compared to control plants (2.63 mg/g) suggesting that C. gloeosporioides helped in value addition of cocultivated C. asiatica in vitro plants. The GC-MS analysis of methanolic extract of cocultivalted and control plants showed that cocultivated plants have higher amount of medicinally important compounds, viz. _-Farnesene, Neophytadine, _-Caryophyllene, Stigmasterol and squalene. GC-MS analysis of ethyl acetate extract of C. gloeosporioides also revealed the presence of 55 bioactive metabolites having immense antioxidant and antimicrobial activity.
Description
Thesis-PhD
Keywords
characterization, endophytic fungi, Centella asiatica , leaves, metabolites, biochemistry, phytochemistry, isolates, antioxidants, fungi