Identification And Characterization Of Endophytic Microbes From Medicinal Plants: Role In Secondary Metabolite Production

Abstract

Background. Endophytes—bacteria, fungi and actinomycetes that inhabit the internal tissues of plants without causing disease—are increasingly recognized as prolific sources of pharmacologically valuable secondary metabolites that complement or even surpass those of their hosts.Methods. Healthy leaves, stems and roots of five ethnomedicinal species (Azadirachta indica, Ocimum sanctum, Withania somnifera, Tinospora cordifolia, Centella asiatica) were surface‑sterilized and plated on selective media. Pure cultures were identified by morphology, 16S rRNA/ITS sequencing and multigene phylogeny. Crude extracts (EtOAc) were profiled by LC‑MS/MS and dereplicated against the GNPS database; prominent metabolites were isolated by semi‑prep HPLC and structurally confirmed (NMR, HR‑ESI‑MS). Bioactivity was assessed by MIC determination against Staphylococcus aureus, Escherichia coli and Candida albicans, and by DPPH/ABTS antioxidant assays.Results. A total of 126 endophytes (67 fungi, 44 bacteria, 15 actinomycetes) representing 23 genera were recovered. Phylogenetic analysis clustered fungal isolates into Fusarium, Colletotrichum, Chaetomium and Aspergillus, while bacteria grouped mainly within Bacillus and Pseudomonas. LC‑MS/MS revealed 71 unique metabolite features, 34 of which were dereplicated as known bioactives (e.g., taxol, chlorogenic acid, cytochalasin D), whereas 16 features showed < 80 % cosine similarity to any reference spectrum, indicating novelty. Several extracts (notably Chaetomium sp. WS‑26 and Bacillus sp. AI‑07) displayed potent antimicrobial activity (MIC ≤ 2 µg mL‑1) and strong antioxidant capacity (IC50 ≤ 15 µg mL‑1). Metabolite yield correlated positively with endophyte colonization frequency (r = 0.79, p < 0.01).Conclusion. Medicinal plants harbour a phylogenetically diverse community of endophytes capable of synthesizing a broad array of bioactive secondary metabolites. Systematic isolation and metabolomic‑guided prioritization can uncover novel compounds with therapeutic potential while providing insight into plant–microbe chemical dialogue.