Antimicrobial and antioxidant activities of endophytes from Tabebuia argentea and identification of anticancer agent (lapachol)

Abstract

Thirteen different endophytic fungi were isolated from different parts of Tabebuia argentea . These endophytic fungal extracts were prepared, using ethyl acetate and evaluated for their phytochemical constituents. Aspergillus niger and Alternaria alternata yielded saponins, phenolic compounds, anthraquinones, steroids, cardiac glycosides and tannins. Other endophytes yielded less phytochemical compounds compared to plant extracts. Naphthoquinone (natural lapachol) was identified in A. niger and A. alternata . These two endophytes also exhibited significant antimicrobial activity against an array of pathogenic fungi and bacteria. Endophytic isolates of A. niger and A. alternata are of particular interest because they showed significant antagonistic activity against all tested bacteria and fungi at different range. The total antioxidant capacity and phenolic content of the fungal cultures ranged from 4299 to 5276 µmol/L and from 2.5 to 2.6 mg gallic acid/100 mL culture respectively. The fungal culture, endophytes, A. niger and A. alternata showed strongest antioxidant capacity, having the highest levels of phenolics. This is the first report of lapachol (naphthoquinone) producing endophytes and their antimicrobial and antioxidant activities. This investigation reveals that the metabolites produced by a variety of endophytic fungi can be a potential source of novel natural antimicrobials, antioxidants and anticancer agents.