A hydrogel-based composite facilitates efficient and recyclable tetracycline biodegradation in aquatic environments.

Tetracycline antibiotics residues pose significant health risks to individual and public health by their cytotoxicity and promotion on antibiotic resistance spread. Tet(X4) is a newly-identified tetracycline-inactivating enzyme that efficiently eliminates all antibiotics within tetracycline class. To address the limitations of Tet(X4)-based approaches in suboptimal stability and cost-efficiency balance in realistic environments, this study established a hydrogel-based composite to encapsulate the Tet(X4) for efficiently and economically eliminating the tetracycline residues in aqueous environments. Herein, we synthesized a composite comprising carboxymethyl chitosan (CC), agarose (Ag), Tet(X4), Fe3O4, and CaO2. It maintained 73.1 ± 9.4 %, 50.0 ± 2.8 % and 58.9 ± 0.6 % of enzymatic activity with desirable tolerance to UV, and ionic strength. By exploring the properties of composites, we found that 3 % Tet(X4) in a 1.0 g weighted composite with average diameters of 5.0 mm could efficiently degrade tetracycline residues. Additionally, the magnetic components in the composite conferred recyclability to the Tet(X4)-dependent biodegradation for multiple use, maximally reducing the costs. The composite endowed the promising applicability of Tet(X4) to eradicate approximately 85 % the residual tetracyclines in various aqueous environments, including tap water, lakes, pharmaceutical wastewater, and livestock sewage. Mouse experiments showed that the as-prepared composites are totally safe and will not cause metabolic and immune abnormalities. Taken together, this study constructed a feasible platform to render the Tet(X4)-mediated tetracycline removal more stable and recyclable, highlighting encapsulation with the nanocarriers as a promising strategy to facilitate the enzymatic degradation of antibiotic residues with enhanced efficiency, stability and recyclability.