Bioreduction of hexavalent chromium and removal mechanisms using Staphylococcus succinus

The microbial reduction of hexavalent chromium (Cr(VI)), particularly by bacteria, has been extensively studied, revealing varying removal mechanisms among different strains. This investigation identified a novel bacterial strain, Staphylococcus succinus subsp. Succinus AMG-D1, which was isolated from mining soil and Cr(VI)-resistant. This strain demonstrated the capability to completely remove a high concentration of 200 mg/L Cr(VI) within 120 h at pH 7 and 35 °C. Moreover, it effectively reduced repeated contamination of 100 mg/L Cr(VI). Scanning electron microscopy analysis confirmed the strain's high resistance to Cr(VI), coupled with the secretion of a viscous material, possibly metal-adsorbing exopolysaccharides. Energy dispersive X-ray peaks analysis revealed characteristic chromium peaks, indicating the presence of adsorbed Cr(VI) and/or precipitated species of reduced chromium (Cr(III)). Further investigations into Cr(VI) removal mechanisms have revealed a detoxification process involving adsorption, accumulation, and enzymatically mediated biological reduction. This reduction predominantly occurs through constitutive cytoplasmic proteins. Moreover, a protein with a molecular weight of approximately 30 kDa was identified on an SDS-PAGE gel, potentially responsible for Cr(VI) reduction. The remarkable resistance and substantial reduction capabilities of Staphylococcus succinus position it as a promising strain for bioremediation applications.