Overexpression of Cysteine Synthetase 1 Promotes Cadmium Removal by Biosynthesizing Cadmium Sulfide Quantum Dots in .

Heavy metal cadmium causes significant contamination in aquatic ecosystems. The biomineralization of cadmium represents a vital biological mechanism for handling cadmium stress in diverse microorganisms. To improve the biomineralization capacity of cadmium by microorganisms in aquatic environments, cysteine synthetase 1 (TtCsa1) was overexpressed in . The tolerance of /pET-28a- to cadmium was enhanced by expressing TtCsa1. Upon addition of cysteine, /pET-28a- generated more HS, which reacted with Cd to form CdS quantum dots (QDs), resulting in a stronger fluorescence signal. The UV-visible absorption and fluorescence spectra of the culture supernatant of /pET-28a- showed characteristic peaks corresponding to CdS QDs. Transmission Electron Microscopy (TEM) images confirmed that the formation of CdS QDs and their agglomeration in the cells. X-ray Diffraction Analysis (XRD) analysis further confirmed the presence of QDs and their crystalline nature. In rich medium, /pET-28a- achieved removal rates of 99.5%, 98.2%, 56.5%, and 49.4%, respectively, for Cd concentrations of 0.15, 0.3, 0.45, and 0.6 mM within 48 h. In simulated wastewater, /pET-28a- achieved removal rates of 99.4%, 94.3%, 90.1%, and 89.8%, respectively, for Cd concentrations of 0.3, 0.45, 0.6, and 0.75 mM within 12 h. These results demonstrate that overexpressing TtCsa1 in can significantly enhance its ability to biomineralize Cd in rich medium and simulated wastewater, which has potential applications in bioremediation of aquatic environments contaminated with heavy metals.