Primary Reserches On The Process Of MC-Degrading Bacterium Isolated From Taihu Lake

Harmful cyanobacterial blooms in eutrophic water body have caused serious pollution of drinding water. Especially, toxin produced by certain cyanobacterial species pose a significant threat to the health of humans and animals. MCs are the most commonly cyanobacterial toxins that can be detected in blooming water. It has been reported that wild and domestic animals died from posinoning due to drinking water containing MCs. Apparently, fish and the other aquatic organisms suffer the thereat because their bodies expose to MCs in polluted water directly.Due to the severe pollution of microcystins in entrophic water, the objectives of this study were as follows:(1) screening MCs-degrading bacterial strain; (2) exploring the behavior of MCs degradation by the strain; (3) isolation and purification of MCs-degrading enzymes.A bacterial strain EMB capable of efficiently degrading microcystins was isolated from blue-green algae stacking pot of TaiHu Lake through acclimatization with MCs extract from algae powder as sole carbon and nitrogen resources. The strain EMB was identified as Bacillus sp. by morphological and physiological properties and 16S rDNA sequence analysis.MC-RR and MC-LR with the concentration of 2.99mg·L-1 and2.15mg·L-1 could be completely degraded by strain EMB within 24h.Further study showed that environmental factors such as temperature, pH value, and nutrition sources, could affect the efficiency of MCs degradation. It was confirmed that strain EMB showed the highest efficiency of MCs-biodegradation when incubated at 30℃and pH 7.0, which could completely degrade MC-RR and MC-LR with the concentration of 2.99 mg·L-1 and 2.15 mg·L-1 within 21h, respectively.The strong ability of MCs biodegradation by strain EMB was probably depended on special properties of MCs-degrading enzymes. The isolation and characterization of the MCs-degrading enzymes was carried on in the following experiment. Cells in EMB culture was removed by centrifugation, and the supernatant was exposed to 80% saturate of (NH4)SO4. After centrifugation, the precipitate was collected and dissolved with PBS followed by dialyzation to remove ions. The dialyzed solution was then separated by ion-exehange chromatography.The 2nd peak that showed MCs-degrading actively was collected and separated by SDS-PAGE. Only one bond was obtained from SDS-PAGE. In addition, a homologue of mlrA gene involved in the degradation of MC-LR and MC-RR was aslo detected in EMB.