Anaerobic Degradation Of Microcystin And Isolation Of Anaerobic Degrading Bacterium

In recent years, with the aggravation of water eutrophication, cyanobacterial blooms become more frequent. Sixty percent of fresh water bodies was under conditins of water eutrophication in our country. The pollution of microcystins is one of the most serious environmental problems in our country. It is imperative to control and eliminate the microcystin pollution. Microbial degradation is the main approach to eliminate microcystin in the environment. Previous studies of microbial degradation of microcystin mostly focused on aerobic environment, but there was few study on biodegradation of microcystin under anaerobic condition. In this thesis, anaerobic degradation of microcystin under different redox conditions was studied in laboratory experiments, and anaerobic MC-degrading bacterium was isolated from Dianchi lake. Moreover, biodegradation process of microcystin by the anaerobic MC-degrading bacterium was investgated. The anaerobic MC-degrading bacterium was identified according to its morphological observation, physiological and biochemical characteristics, sequences of 16S rDNA. The main conclsions obtained are listed as follows:1. Anaerobic degradation of microcystin under different redox conditionsWe studied the degradation of microcystin-LR and reduction of electron acceptors under different redox conditions. The results showed that microcystin-LR could be degraded rapidly under methanogenic condition, demonstrating that fermentative bacteria may participate in the degrading process of microcystin-LR. Although microcystin-LR could also be degraded under sulfate-reducing conditions, sulfate-reduction was not observed over the 10 days of incubation, and 10 mmol·L-1 sulfate-reducing bacteria inhibitor did not inhibited the degradation of microcystin-LR, these results indicated that sulfate-reducing bacteria did not participate in the degrading process of microcystin-LR. Nitrate was reduced under nitrate-reducing condition, but no biodegradation of microcystin-LR was detected, it indicated that nitrifying bacteria cannot utilize microcystin-LR as an electron donor.2. Isolation of the anaerobic MC-degrading bacterium and the biodegradation process of microcystinOne anaerobic MC-degradation bacteria was isolated from the sediment of Dianchi lake via incubation on solid medium. The MC-degrading bacterium designated CJ5 could degrade MC-LR of 5 mg·L-1 to below the detection limsts within 4 d. In the organic medium, strain CJ5 came into the exponential phase and stationary phase after 12 h and 36 h, respectively.3. Identification and conservation of strain CJ5The colony of CJ5 on anaerobic solid organic medium was round,1～2 mm across, slippery and limpid, with regular edges and a moist surface. Strain CJ5 is a gram-negative bacillus, with ability of motility, no capsule and no spore. Based on the analysis of colonial morphology, physiological and biochemical characteristics and the 16S rRNA gene sequence, the bacterium was indentified as Acidaminobacter sp.Anaerobic MC-degrading bacterium CJ5 was preserved by means of minimal medium conservational method, rich organic conservational method, glycerol-saline conservational method, half volume of flycerol and bacilli conservational method and filter paper conservational method. The results suggested that the bacterium could maintain ites degrading activity under the conservation method of solid medium with rich organic conservational method in 3 months. So this method was chosen to conserve the anearobic degrading bacterium CJ5.