Endophytic fungi from Nerium oleander L (Apocynaceae): main constituents and antioxidant activity

Abstract

Diverse endophytic fungi exist within plant aerial tissues, with a global estimate of up to a million undescribed species. These endophytes constitute a rich bio-resource for exploration to discover new natural products. Here we investigate fungal endophytes associated with a medicinal plant, Nerium oleander L. (Apocynaceae). A total of 42 endophytic fungal strains were isolated from the host plant. Total antioxidant capacity, xanthine oxidase inhibitory activity, antimicrobial activity, and total phenolic content (TPC) were evaluated for 16 representative fungal cultures grown in improved Czapek's broth and for the host plant. The total antioxidant capacities and phenolic contents of the fungal cultures ranged from 9.59 to 150.79 lmol trolox/100 mL culture, and from 0.52 to 13.95 mg gallic acid/100 mL culture, respectively. The fungal culture of an endophytic strain Chaetomium sp. showed the strongest antioxidant capacity, contained the highest level of phenolics, and to some extent inhibited xanthine oxidase activity with an IC 50 value of 109.8 lg/ mL. A significant positive correlation was found between antioxidant capacity and TPC in the tested samples. Most of the endophytic fungal cultures tested have a wide range of antimicrobial activities, which were not very strong, but much better than those of the host plant. The major bioactive constituents of the fungal cultures were investigated using LC-ESI-MS and GC-MS, and preliminary identification detected phenolics (e.g. phenolic acids and their derivatives, flavonoids) and volatile and aliphatic compounds. This study shows that the endophytic fungi isolated from N. oleander can be a potential antioxidant resource.

Bioactive metabolites from an endophytic fungus Penicillium sp. isolated from Centella asiatica

“…Strobel et al (2002) & Harper et al (2003 obtained two antioxidants, pestacin and isopestacin, from the endophytic fungus Pestalotiopsis microspora. The endophytic fungi residing in Nerium oleander were shown to have excellent antioxidant capacity and preliminary identification detected phenolics and volatile and aliphatic compounds by Huang et al (2007). The results of this study are similar to those in previous reports and indicate that endophytic fungi may serve as a potential source of antioxidants.…”

Secondary metabolites from endophytic fungus from Lippia sidoides Cham.

“…Hence, an appreciable amount of flavonoids produced by the endophytic fungi may be present in the quantity verified in the plant; moreover, they contributed to its synthesis. Huang et al (2007) isolated 42 endophytic fungi from Nerium oleander and found flavonoids among the main bioactive compounds of some cultures. They also clarified that some phenolic compounds are produced so that certain endophytic fungi survive along with their host plants.…”

Antitumor and antimicrobial activities of endophytic fungi from medicinal parts of Aquilaria sinensis

“…Most endophytes are capable of synthesizing bioactive compounds that may provide plants with a defense against pathogens, and some of these compounds have proven useful for novel drug discovery (Guo et al, 2008;Yan et al, 2011). Since the chemical constituents from medicinal plants were complex, more and more endophytic fungi with novel metabolites of pharmaceutical importance were isolated from medicinal plants, and a series of new and useful compounds were obtained (Huang et al, 2007;Guo et al, 2008;Kusari et al, 2009). No doubt, exploiting a variety of new natural products from endophytic fungi of medicinal plants has become a hot spot of new drug research.…”