High-efficient and sustainable biodegradation of microcystin-LR using Sphingopyxis sp. YF1 immobilized Fe₃O₄@chitosan

The microcystin-LR (MC-LR) produced due to harmful cyanobacterial blooms have brought great harm to human and aquatic organisms, attracting a wide public health attention. To deal with MC-LR contamination, we synthesized a novel bio-functionalized composite for the high-efficient and sustainable biodegradation of microcystin-LR by covalent immobilizing Sphingopyxis sp. YF1 onto chitosan-grafted Fe₃O₄ magnetic particles (Fe₃O₄@CTS). The Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM) were utilized to characterize the structural properties of Fe₃O₄@CTS/Sphingopyxis sp. YF1. The immobilization conditions were optimized. And the MC-LR-degrading capabilities of Fe₃O₄@CTS/Sphingopyxis sp. YF1 were assessed under various conditions. The results showed that the optimal immobilization conditions containing 1.0 % (v/v) glutaraldehyde, immobilization for 4 h at 30 ℃. The Fe₃O₄@CTS/Sphingopyxis sp. YF1 showed an attractive degradation performance which possesed a wide torlerance to pH (6.0-9.0) and temperature (25-35 ℃). More interesting is that the Fe₃O₄@CTS/Sphingopyxis sp. YF1 exhibited significantly increased MC-LR-degrading capabilities after recycling and reusing which degradation rate reached 1.50 μg/mL/h in the sixth cycle, and it was easily recycled by using a magnet (Ms 21.5 emug^-1). Two intermediates (tetrapeptide and Adda) and three degradation related genes (mlrA, mlrB and mlrC) were obtained in this study and the pathway for the degradation was proposed. These results revealed that Fe₃O₄@CTS/Sphingopyxis sp. YF1 can be potentially used for treatment of MC-LR contaminated environment.