| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 96 === The effect of chlorination on the cell integrity and metabolite release from three nauseous cyanobacteria, including Microcystis aeruginosa, Anabaena circinalis, and Cylindrospermopsis raciborskii, is investigated. The cyanobacteria were grown in the filtrated water from Tai-Lake, Kinmen, with addition of ASM algae growth medium. A fluorescence technique, combining fluorescein diacetate (FDA) with either flow cytometer or epifluorescence microscope, was successfully developed for the determination of cell integrity. A solid-phase microextraction (SPME) concentration followed by a gas chromatograph (GC) and mass spectrometric detector (MSD) was employed to measure the metabolites from the cyanobacteria. A series of chlorination of cyanobacteria-laden water was conducted at different cell concentrations and different chlorine dosages. During the experiments, chlorine concentration, cell integrity, metabolite concentration, and other water quality parameters were monitored at different time. The experimental results revealed that both Microcystis and Anabaena cells are very fragile to chlorine. At an initial chlorine concentration of 2-4 mg/L, almost 80 - >90% of Microcystis and Anabaena cells were ruptured at 2-5 minutes, causing immediate release of metabolites from the cells. For Cylindrospermopsis, however, is more resistant to chlorine. Only ~20% of cells were ruptured at chlorine = 4 mg/L and contact time = 30 minutes. Scanning electro-microscope photos also confirmed that chlorine did have strong impact on the three tested cells. After chlorination, Microcystis cell surface was deformed and became less smooth, and the filamentary Anabaena and Cynlindrospermopsis cells were ruptured and broken into single cells.
The major nauseous metabolite of Anabaena, geosmin, was released into water immediately after the cells were rupture. The geosmin concentrations in the water followed a similar trend of the ratio of ruptured cells, suggesting that geosmin may also serve as an indicator of cell integrity for Anabaena. For Microcystis, the aqueous phase of β-cyclocitral, the major metabolite monitored, did not increased as the cells disrupted for most of the cases, even that most cells were not integral. β-cyclocitral is known to be produced from a rapid reaction of oxygen, β-carotene, and enzymes present in the cells, oxygenase. The chemical is only largely formed after the cells are ruptured. Therefore, it is very likely that the enzymes reacted with chlorine righter after the cells were broken, causing inhibition of β-cyclocitral formation.
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