Heavy metal tolerance and biosorption efficiency of Lysinibacillus fusiformis SKT23 novel strain for Zn and Cu removal

Bioremediation offers a sustainable strategy for removing heavy metals from water by transforming toxic pollutants into less hazardous forms. In this study, a highly metal-tolerant bacterium, Lysinibacillus fusiformis strain SKT23 (accession PX488931), was isolated from contaminated soil in Fayoum, Egypt, and identified via morphology, biochemical tests, and 16S rRNA sequencing. The strain exhibited optimal growth at 50 ppm Zn (pH 7, 30 °C) and 50 ppm Cu (pH 8, 30 °C) in mineral salt medium, with growth monitored through optical density and protein content. SEM, TEM, and EDX analyses revealed cell surface modifications, intracellular and extracellular metal deposition, and precipitate formation under metal exposure. The adsorption performance of the prepared material was assessed through isotherm modeling and treatment of real wastewater. Isotherm modeling showed that Cu2⁺ and Zn2⁺ biosorption onto bacterial biomass followed Freundlich and Langmuir models, with n values (2.22–2.38) indicating favorable adsorption and qm values up to 120 mg/g, confirming the strong affinity of metal ions toward bacterial cell surface binding sites. In synthetic solutions, removal reached 98 ± 0.5% for Cu and 92 ± 0.7% for Zn at 50 mg/L, while in real wastewater it remained 88 ± 1.0% and 85 ± 1.2%, respectively. These findings demonstrate that L. fusiformis SKT23 possesses high metal tolerance, robust adsorption capacity, and effective removal efficiency in both controlled and complex environments, highlighting its practical potential for sustainable bioremediation of Cu and Zn contaminated water.