Isolation and characterization of endophytic bacteria from Echinacea purpurea and Calendula officinalis with...

Endophytic bacteria are increasingly recognized as a promising source of biologically active secondary metabolites with potential biomedical applications. This study aimed to evaluate the antimicrobial and anticancer activities of secondary metabolite extracts derived from endophytic bacteria associated with Echinacea purpura (E. purpurea) and Calendula officinalis (C. officinalis).

Bacterial endophytes were identified using phenotypic characterization and 16 S rRNA gene sequencing. Secondary metabolites were extracted using ethyl acetate and evaluated for antimicrobial activity using agar well diffusion and broth microdilution assays, including determination of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum fungicidal concentration (MFC). Cytotoxic and apoptosis-inducing effects were assessed using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) and flow cytometry assays. Chemical profiling was performed using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS).

Three isolates (SM.Ep01, SM.Co01, and SM.Co05) demonstrated measurable antimicrobial activity, predominantly against Gram-positive bacteria. SEM analysis revealed structural alterations in bacterial cells following treatment. Crude metabolite extracts induced dose-dependent cytotoxicity and apoptosis in cancer cell lines. FTIR and GC-MS analyses revealed diverse functional groups and tentatively identified compounds previously associated with biological activity.

These findings provide preliminary evidence that endophytic bacteria associated with E. purpurea and C. officinalis may represent potential sources of biologically active metabolites.