Polyphasic characterization, bioactive potential and metabolite profiling of Streptomyces violaceoruber R6 isolated from Ocimum tenuiflorum

The emergence of antimicrobial resistance necessitates the exploration of novel bioactive compounds. We conducted this study to explore the biological capabilities of R6, an endophytic actinomycete isolated from Ocimum tenuiflorum. The strain exhibited significant antibacterial activity, particularly against ESBL-producing Escherichia coli (20 mm) and Klebsiella pneumoniae (25 mm). Moderate antifungal activity was also observed against Aspergillus fumigatus (9–10 mm). Cytotoxicity screening using the MTT assay revealed 75% cell mortality at 100 mg/mL against Baby Hamster Kidney fibroblast (BHK-21) cell lines. Thin-layer chromatography (TLC) and HPLC-UV/Vis analysis indicated the presence of polyketides, indoles, and amines, suggesting the synthesis of biologically active compounds. The detection of type I polyketide synthase (PKS-I) gene cluster further confirmed its potential for synthesizing novel secondary metabolites. Genetic identification through analysis of 16 S rRNA sequencing and phylogenetics indicated it to be Streptomyces violaceoruber. To the best of our understanding, this is the first report of the isolation of Streptomyces violaceoruber from the medicinal plant, Ocimum tenuiflorum. These findings support the prospect of medicinal plant endophytes as a potential source of antimicrobial and cytotoxic compounds, encouraging further research on their pharmaceutical applications.