Bioactivity assessment of endophytic fungi associated with Citrus macroptera Montr.: an endangered ethnomedicinal plant used in folk medicines in North-East India

Thirteen endophytic fungal isolates, inhabiting Citrus macroptera growing in Assam, India, were studied for their ability to produce bioactive metabolites. Ethyl acetate extracted secondary metabolites of endophytic Talaromyces assiutensis, exhibited the highest antimicrobial activity against Staphylococcus epidermidis followed by Acremonium falciformae which inhibited Sclerotinia sclerotiorum. Taxonomic identity of T. assiutensis was confirmed by internal transcribed spacer r-DNA sequence analysis. Quantitative estimation of phytochemicals of the ethyl acetate extracted secondary metabolites produced by T. assiutensis, revealed that flavonoid content was the highest followed by alkaloids, saponin and terpenoids. FT-IR spectrophotometry of the extract showed the presence of alcohol, alkane, acid anhydride, alkene, aromatic, alkyl halide and amine as functional groups. Nine major cmpounds, viz., 3-undecene-5-methyl-; 2,5-dihydroxy-3-methyl-2,5-cyclohexadiene-1,4-dione; 3- n -hexylthiolane, S,S-dioxide; Methyl 8-Methylnonanoate; (4H)4a,5,6,7,8,8a-Hexahydrobenzopyran-5-one-3-carboxamide,2; Cyclopentane undecanoic acid, methyl ester; Trans-2,4-Dimethylthiane, S,S-dioxide; 5-Hydroxy-4-hydroxymethyl-1-(1-hydroxy-1-isopropyl)-Cyclohex-3-ene and 3-Nonyn-1-ol were identified from the bioactive metabolites of T. assiutensis using GC–MS. The results indicate that the antimicrobial compounds produced by T. assiutensis may be used in pharmaceutical as well as agricultural industries.