Biodegradation Of Microcystin By Immobilized Microcystin-degrading Bacteria

Microcystins (MCs) are a family of intracellular toxins produced by cyanobacteria bloom in nature water body. Toxic cyanobacterial blooms are on the increase, presenting severe threat to human health. In this paper, the microcystin-degrading bacteria, X20, was immolilized and the ability of degradation for MCLR measured. The main contents are listed as follow:The best carrier for immobilization was selected. In the next step, the biodegradation of MCLR by immobilized X20 was investigated. We also studied the effect of environmental factors on the degradation progress of MCs, using seleted material as carrier to immobilized X20. The degradation dynamics of immobilized cells was investigated. Finally, the conserve method of immobilized cells was explored. The main results are listed as follow:1) Toxic test of immobilization regents showed that the activity of cell was strongly inhibited by boric acid, and CaCl2 had no obvious effect on the activity of X20. Orthogonal experimental results show that the immobilized beads made by Na.Alg alone are more flexible, the performance of mass transfe is better, and the rate of biodegradation is faster. So the best material was confirmed, Na.Alg. The optimized condition was 3% Na.Alg,8% CaCl2, the cell mass is about 1.8 X 107cells/ml, and the crosslinking time is 1h.2) This material was used for immobilization of the bacteria, and the ability of the immobilized cells for MCLR was measured, the results shows that MCLR (5 mg/L) was degraded to below the detection limit (0.5mg/L) in 4 days, the effects of cultivate temperature, initial pH and nutrient amended on the MCLR degradation by immobilized cells were investigated, and we know that temperature could affect the activity of the immobilized cells, the rates of microcystin-LR biodegradation increased with increasing incubation temperature between 20 to 30℃. There was no difference along with different acidic or alkaline conditions and the addition of glucose, nitrogen or phosphorus had no obvious effect on the biodegradation of microcystin-LR. The result of further research showed that the immobilized cells could biodegraded MCLR (10μg/L) in environment below the detection limit (1μg/L) in 6 days. The immobilized cells still have strong during three cycles of repeated cultivation. 3) The test about degradation dynamics of immobilized cells showed that the degradation process of microcystin-LR by immobilized cells could be described by first-order reaction:c=ea+kt.4) The experiment of conserve showed that the immobilized cells could keep activity conserved in dry, tap water after 10d, but the immobilized cells had strong degradation activity which conserved in lake water containing MC water after 60d.