Pharmacological assessment of the extract and a novel compound of Bacillus velezensis DM derived from the rhizosphere of Datura metel L. with microbial molecular screening.

Background: Rhizosphere bacteria were considered a prospective reservoir of bioactive compounds with significant pharmacological efficacy.

Methods: From the rhizosphere of Datura metel L., Bacillus velezensis DM was isolated and characterized using 16 S rRNA. PCR screening and sequencing were conducted to identify genes related to bioactive metabolite production. The extraction of secondary metabolites from the bacterial strain was performed via a fermentation process. The ethyl acetate extract of the propagated strain was subjected to fractionation and purification through various chromatographic techniques. The characterization of the isolated compounds was accomplished using different spectroscopic methods, such as 1D and 2D-NMR. An MTT test was conducted to assess the cytotoxic activity of bacterial extract on MCF-7, HepG-2, and HCT-116 cells. Furthermore, its pure compound (1) was tested for its cytotoxicity on HCT-116 and a normal cell (THLE2) to test its safety for normal cells. Apoptosis was identified through flow cytometry on HCT-116 cells after double-staining with PI and annexin V-FITC. The antioxidant action of bacterial extract was assessed through DPPH and ABTS assays. Furthermore, anti-inflammatory evaluations were carried out employing lipoxygenase (5-LOX) and cyclooxygenase (COX-2) inhibition.

Results: The NCBI GenBank database has effectively incorporated the 16 S rRNA gene sequence of Bacillus velezensis DM under the accession number OR364492. Polyketide synthase and two lipopeptide genes for surfactin and iturin A were effectively detected by PCR, and their sequences were included in the Genbank database. A novel compound, 5,6-di(methylamino)hex-5-ene-1,2,3-triol (1), was successfully separated from the strain. Bacterial extract demonstrated significant cytotoxic activity against the evaluated cancer cells, exhibiting the most pronounced effect on HCT-116 cells. Compound (1) showed promising cytotoxic potential against HCT-116 cells with a higher selectivity index (2.5) towards cancer cells in comparison to Doxorubicin (1.49). Apoptosis assay showed that bacterial extract caused apoptosis about 14 folds compared to the control HCT-116 cells. Furthermore, it showed a potent anti-inflammatory outcome (IC₅₀ = 1.927 µg/mL) and antioxidant activity at IC₅₀ of 76.8 µg/mL.

Conclusion: This study revealed the possible pharmacological effects of secondary metabolites generated by Bacillus velezensis DM, making it a valuable resource for isolating bioactive compounds with potential therapeutic and biomedical uses.