Study On Anaerobic Degradation Of Microcystins

In recent years, harmful algae blooms(HABs) occurred frequently with the increase of eutrophication all over the world. After algae blooms, many algaes died and released many toxins, among which Microcystin(MC) is the most frequent and harmful. Hence, reducing the pollution caused by MC has become the hottest topic in the field of environment. So far, biodegradation is one of the most effective methods in removing or reducing the content of MC that can pollute the environment. At present, aerobic biodegradation of MC has been considered to be the main attenuation, anaerobic biodegradation is rarely studied. In addtion, the anerobic biodegradation pathway of MC remains unclear. Therefore, the biosynthesis of MC-LR in Microcystis aeruginosa, the anaerobic biodegradation of MC-LR and the degradation mechanism of MC-LR were mainly focus in the thesis. The specific contents are as follows:In the paper, 15NH4 Cl was the sole nitrogen source during the cultivation of Microcystis aeruginosa. The decrease of 15NH4 Cl content was almost consistent with the growth of the cells, which indicated that amonium was the sole nitrogen source aborbed by Microcystis aeruginosa. In addition, the full 15N-labeled MC-LR was successfully biosynthesised in Microcystis aeruginosa by using the liquid chromatography-mass spectroscopy(LC-MS) technique and Raman spectroscopy after six culture tansfers. The labeled sequence of 15N-MC-LR was Adda, Ala, Me Asp, Arg, Leu, Mdha, Arg, Glu.MC-LR was the sole carbon and nitrogen source to cultivate the LW and CT anerobic microbial consortium. The degradation rate of MC-LR could reach 89% within 7 days in LW anerobic microbial consortium. The result of 16 S r RNA sequencing analysis showed that Bacteroidetes(61.09% 、 9.58%), Proteobacteria(2.48% 、 42.62%), Spirochaete(20.36%、9.34%), Firmicutes(7.63%、4.64%) are the dominant Phyla, respectivly. The result indicated that there are six degradation products of MC-LR under anoxic conditions. Two products were intermediate metabolite and four were final. Furthermore, the MC-LR was converted into linear structure first, and degraded into tetrapeptide and small molecular like the Adda residue.In the thesis, we also studied the degradation mechanism of MC-LR by extracting the crude enzyme in LW anerobic microbial consortium. The result indicated the intracellular crude enzyme played a vital role in degradation of MC-LR.