Bacterial laccase immobilized on a magnetic dialdehyde cellulose without cross-linking agents for decolorization

Abstract In the process of using cross-linking method to immobilize enzymes, cross-linker have a certain negative effect on immobilization efficiency. In this study, a magnetic dialdehyde cellulose (MDAC) was prepared by oxidizing hydroxyl groups in cellulose to aldehyde groups. The modified cellulose could be used for the immobilization of bacterial laccase without cross-linker. The morphology and structure of the MDAC–laccase complex (MDAC-L) confirmed that the laccase was immobilized on MDAC via -CHO in MDAC and -NH2 in laccase. Under conditions of pH 4 and 45°C, the maximum loading capacity of MDAC-L reached 210.74 mg/g, and relatively high enzyme activities maintained,. Compared with free laccase and immobilized laccase with glutaraldehyde, MDAC-L exhibited a wide pH range, temperature stability, reusability, and is suitable for long-term storage at low temperature. MDAC-L also improved the tolerance of free laccase to the presence of organic solvents, inhibitors and metal ions. Furthermore, the maximum saturation magnetization of MDAC-L was 34.07 emu/g, allowing for rapid magnetic separation. The relative activity of the immobilized laccase remained about 70% after 10 cycles of reuse. In addition, MDAC-L showed good decolorization performance when applied to crystal violet. Under the conditions of 45 °C and pH 6 for 21 h, the decolorization rate can reach about 90%. This study developed a novel cross-linking method for enzyme immobilization.