Beneficial Endophytic Bacteria Associated with Medicinal Plant Vernonia anthelmintica flowers: Characterization and Biological activities

Abstract Endophytic bacteria associated with medicinal plants are a vital component of the plant microbiome and represent a valuable biological resource. This study investigates the diversity and biological activities of endophytic bacteria isolated from the flowers of Vernonia anthelmintica, a medicinal plant native to China. The research focuses on evaluating the cytotoxic, antimicrobial, antioxidant, and antidiabetic properties of natural products derived from these bacteria, as well as their effects on melanin synthesis and tyrosinase activity in B16 cells. A total of 32 bacterial strains were isolated and cultured, of which eight crude extracts exhibiting antimicrobial activity were selected for further analysis. These isolates were identified as Bacillus paranthracis XJB-1, Bacillus safensis XJB-51, Bacillus pumilus XJB-30, Bacillus halotolerans XJB-36, Bacillus subtilis XJB-57, Streptococcus lutetiensis XJB-76, Priestia megaterium XJB-41), Paenibacillus alvei XJB-13). Among them, P. megaterium XJB-41 demonstrated the strongest pharmacological potential, warranting further investigation to optimize its culture conditions for enhanced bioactive compound production. The optimal growth conditions for P. megaterium XJB-41 were determined to be LB and Nutrient Broth (NB) media, with peptone as the carbon source and yeast extract as the nitrogen source, under a 24-hour incubation period. These conditions significantly enhanced both bacterial growth and metabolite yield. Moreover, two secondary metabolites: cyclo(D-leu-L-pro) 1 and 2-benzoxazolone 2 were isolated for the first time from the ethyl acetate fraction of P. megaterium XJB-41. This strain shows significant promise as a natural source for the development therapeutic agents targeting vitiligo, cancer, and infectious diseases.