Study Of Microcystin Biodegradation By Microorganisms In Aquatic Environment

Biodegradation of microcystins (MC) by microorganisms is one of the main ways of MC removal in aquatic environment. Up to now MC-degrading bacteria isolated from surface water are aerobic. The pathways and main species involved in the anaerobic degradation of MC at bottom and sediments of water bodies are still poorly understood. The objectives of this study is to optimize the MC extraction method from natural blue-green algal bloom to obtain sufficient amount of MC for the experiments, and to study the biodegradation efficiency under aerobic and anaerobic conditions, and to isolate the main degradating bacteria, especial the anaerobic bacteria, from eutrophicated water samples and sediments from collected from different locations of China.The extraction method of MC from blue-green algal bloom was optimized in this study. By comparing different solvents and extraction time, 5% acetic acid was found to be an optimum solvent for extracting MC-RR, the continuous extraction method could obtain more MC-RR and MC-LR from cyanobacterial cells than the other methods. The phycobiliproteins in extract solution, which having negative effects on ODS (C₁8) cartrideges, was removed by 5% acetic acid solvents directly, and by this method the step of adjusting the pH of solvents to remove phycobiliproteins can be omitted.Dominant bacteria separated from eutrophicated water samples showed MC degradation ability. This indicates that MC degradation is widely occurred in aquatic environment. Dominant bacterium W-2 was isolated and showed different degradation efficiencies under different MC concentrations. In low concentration (MC 2mg .L-1) it showed higher degradation ability and could degrade 63.5% of MC in 7 days; when MC is 10 mg.L-1, the degradation efficiency declined, and it only degraded 30% of MC in 7 days; and when MC concentrations was higher than 10 mg .L-1, it showed no degradation ability. The result may due to the inhibition of bacteria growth at high MC concentrations. It was found that the sediment microbeshave higher MC degradation ability than that of the water column.MC degradation under anaerobic condition of sediments collected from eleven lakes of China was investigated. HPLC chromatograms showed diverse pathways of MC degradation. The degradation of MC showed positive relationship with TN, TP, and COD of the sediments. The differences of growth, species and cell density of bacteria directly correlated with the degradation and transformation of MC. In this study the first anaerobic MC-degrading bacterium (D7-1) was isolated and purified, and which was identified as Proteus sp.( Enterobaceriaceae).