Abstract
Bacillus species are prolific producers of biosurfactants with promising environmentally sustainable applications. In this study, biosurfactant production by the wheat endophytic Bacillus sp. WL2-23, isolated in a previous study, was optimized using a Taguchi orthogonal array design. Eighteen media formulations were evaluated by varying carbon and nitrogen sources, pH, and temperature. The optimal medium (glycerol and peptone at pH 8 and 30 °C, 120 rpm) yielded maximum biosurfactant production utilizing a 2% (v/v) inoculum. The crude biosurfactant exhibited high emulsification indices (> 80%) against various hydrocarbons (toluene, hexane, kerosene, and petrol) and demonstrated the highest oil displacement activity. Furthermore, the biosurfactant maintained stability across broad pH (4–9) and temperature (4–100 °C) ranges, although activity declined under saline conditions, completely disappearing at 7% NaCl. Preliminary structural characterization using Thin Layer Chromatography (TLC) and Fourier Transform Infrared Spectroscopy (FTIR) suggested the presence of lipid and peptide moieties, indicating a lipopeptide-like nature. Additionally, Bacillus sp. WL2-23 exhibited substantial growth in medium containing diesel as the sole carbon source. Supplementation with its partially purified biosurfactant (30 µg mL⁻¹) significantly enhanced this bacterial growth. The results highlight the robust biosurfactant-producing potential of the wheat endophyte Bacillus sp. WL2-23 and suggest its potential utility in supporting microbial growth in hydrocarbon-contaminated environments.