Evaluation of antibacterial and anticancer properties of secondary metabolites isolated from soil Bacillus spp focusing on two strains of Bacillus licheniformis and Bacillus siamensis.

Background: Bacillus strains are well recognized for their inherent production of bioactive compounds that exhibit antibacterial and anticancer properties. This study aims to evaluate the antimicrobial and anticancer effects of the secondary metabolite isolated from Bacillus licheniformis and Bacillus siamensis strain.

Material and method: We developed and purified a new soil-derived Bacillus strain to study its metabolites on cancer cells and bacteria. After evaluating the antimicrobial effects of the selected strains' secondary metabolites by well diffusion, growth conditions and temperature optimised using liquid-liquid extraction, secondary metabolites isolated, and active compounds identified using GC-MS. Evaluation of PC-3 and HPrEpC cytotoxicity. AV/PI staining and comet assay assessed necrosis and apoptosis. Real-time PCR measured apoptotic gene expression. Finally, the scratch test measured cell movement.

Results: Bacillus strain metabolites exhibit dual-purpose antimicrobial and anticancer properties. Bacillus licheniformis isolate 56 and S2-G12 isolate 60 demonstrated the greatest antibacterial activity. Among all Bacillus isolates, isolates 56 (Bacillus licheniformis) and 60 (Bacillus siamensis strain) had the highest antibacterial activity. Crude extracts obtained from strains 56 and 60 decreased PC-3 cell viability in a dose-dependent manner. At 200 µg/mL, the survival rate of cells treated with strain 56 and 60 crude extract was 23% and 25%, respectively (p < 0.001). The treatment of PC-3 cells with strains 56 and 60 crude extract led to considerable apoptosis (46.2% and 50.09%, respectively) compared to the control group. After treatment with the crude extract from strains 56 and 60 at an IC₅₀ concentration, a significant number of PC-3 cells showed comet formation, indicating DNA fragmentation. Metabolites extracted from strain 56 and 60 enhanced caspase 3, caspase 8, and Bax genes expression and reduced Bcl-2 expression (p < 0.001). Cell migration was also prevented.

Conclusion: Our findings show that the secondary metabolites of B. licheniformis and B. siamensis have antibiotic and anticancer properties. However in vivo studies are necessary to confirm these findings.