Production and Characterization of a Lipopeptide Biosurfactant from Bacillus velezensis SHB.28 Using Date Syrup for Heavy Metal Removal

Biosurfactants are environmentally friendly surface-active compounds with promising applications in environmental remediation. In this study, a biosurfactant-producing bacterium, Bacillus (B.) velezensis SHB.28, was isolated from heavy metal-contaminated soil and evaluated for its ability to produce biosurfactants using date syrup as a low-cost agro-industrial substrate. Screening assays including drop-collapse (DC), oil spreading (OS), and emulsification index after 24 h E24 (%) confirmed strong biosurfactant production. Culture conditions were optimized, revealing that 30 °C, pH 6, and a C/N ratio between 10% and 20% provided optimal production. Under optimized conditions, the crude biosurfactant extract yield reached 2.16 g/L within 24 h, accompanied by a reduction in surface tension from 69 to 29.1 dyn/cm and high emulsification activity. Kinetic modeling showed that emulsification activity followed an exponential growth model (R2 = 0.985), whereas surface tension dynamics were well described by a spike decay–plateau model (R2 = 0.998). Structural characterization using Fourier-transform infrared spectroscopy (FTIR), electrospray ionization–mass spectrometry (ESI–MS), and nuclear magnetic resonance (NMR) spectroscopy revealed that the biosurfactants are surfactin- and iturin-like cyclic lipopeptides composed of a β-hydroxy fatty acid chain (C13–C15) linked to a cyclic peptide moiety. The biosurfactant exhibited a critical micelle concentration of 100 mg/L and an anionic character with a pHpzc of 5.7. Furthermore, it demonstrated high efficiency in removing heavy metals, achieving removal efficiencies of 99.88% for Fe2+, 99.69% for Pb2+, and 94.72% for Cu2+, outperforming conventional surfactants such as SDS and Tween 80. These findings highlight the potential of date syrup-derived surfactin and iturin from B. velezensis SHB.28 as sustainable and efficient biosurfactants for environmental remediation and heavy metal removal applications.