The Effect of Cadmium and Hydrogen Peroxide on Bioactive Metabolite Production in Endophytic Bacillus Isolates from Solanum nigrum

Bacterial endophytes isolated from medicinal and wild plant species have recently gained significant attention for their medicinal properties, often closely linked to those of their plant hosts. This study identified two endophytic Bacillus isolates using 16S rRNA sequencing-based phylogeny. The impact of sublethal concentrations (0.5 mg/mL) of cadmium and hydrogen peroxide on metabolite production and bioactivity was also investigated. Phytochemical testing and antimicrobial and antioxidant assays revealed shifts in metabolite production under stress conditions. According to the phylogenetic analysis, Bacillus sp. NV35 and NV1 are respectively related to Bacillus cereus and B. mycoides. Phytochemical screening of methanolic crude extracts from both isolates tested positive for alkaloids, flavonoids, and saponins. Notably, tannins were detected only after cadmium treatment, while steroids were present following exposure to both cadmium and H2O2. LC-MS fingerprinting confirmed the presence of several tannins and steroids in treated samples. The untreated crude extracts exhibited an IC50 of ~3 mg/mL with the DPPH assay, which decreased to ~1.5 mg/mL after treatment with cadmium or H2O2, demonstrating enhanced antioxidant potential under stress conditions. Additionally, extracts from both treated and untreated bacteria displayed antimicrobial activity against selected bacterial pathogens, with MIC values ranging from 62.5 μg/mL to 125 μg/mL. LC-MS analysis identified various antimicrobial and antioxidant metabolites, including phenoxymethylpenicilloyl, maculosin, (S,R,S)-alpha-tocopherol, 3-indoleacrylate, procyanidin A2, cis-11-eicosenamide, 3-hydroxy-3-phenacyloxindole, and 9-octadecenamide.