Genomic and spectroscopic analysis for antimicrobial metabolite profiling of Microbacterium testaceum endophyte

Wild plants harbor distinct endophytes that produce potent antimicrobial metabolites that can be used to combat life-threatening pathogens. In our study, four bacterial endophytes (LP1, LP2, LP3, LP4) were isolated from the inner tissues of leaves of Pluchea dioscoridis (L.) DC (Barnûf). The antimicrobial activity of the respective extracts (P1, P2, P3, and P4) against standard, multidrug-resistant (MDR), and Candida albicans was determined using the cup agar diffusion method. The P4 extract showed broad-spectrum activity against all tested pathogens and promising antiviral activity. The endophytic bacterium LP4 was microscopically and genomically identified by whole-genome sequencing (WGS) as Microbacterium testaceum (M. testaceum) strain CCASU-2025-88. The extract of endophytic M. testaceum CCASU-2025-88 (LP4) exhibited broad-spectrum antimicrobial activity against standard and multidrug-resistant pathogens as well as antiviral activity against Adenovirus 7, Herpes Simplex Virus 1, and Herpes Simplex Virus 2, and cytotoxic activity with a non-toxic concentration of 7.32 μg/mL, reflecting the promising bioactive properties of LP4 metabolites. Chemical profiling using AntiSMASH and LC-ESI-MS analysis suggested the presence of a compound putatively identified as microansamycin B; however, this assignment remains tentative, since the compound exhibits potent antibacterial activity, and it demonstrates the bioactive potential of M. testaceum metabolites. In conclusion, M. testaceum strain CCASU-2025-88 is a potential source of microansamycin B-like compound based on LC-ESI-MS evidence. This is the first report investigating the production of microansamycin B by a locally isolated endophytic bacterium, M. testaceum CCASU-2025-88. Further studies are recommended to optimize its production and isolation in a pure form.