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This thesis reports the effect of the non-toxic cyanobacterium Oscillatoria agardhii CYA29 and its spent medium on the cell-bound toxin levels in Microcystis aeruginosa PCC7820 and Nodularia sp. PCC7804. Microcystin levels were elevated when O. agardhii or its spent medium were added to cultures of M. aeruginosa PCC7820. This effect was also observed for two nodularin variants in Nodularia PCC7804. However, growth of M. aeruginosa in its own spent medium did not lead to elevated microcystin levels. Some Gram-negative bacteria use quorum sensing, the determination of population density by pheromones, to regulate the expression of traits in a density dependent manner. The presence of the bacterial pheromones, acyl-homoserine lactones (AHLs), was investigated in cyanobacteria and a simple and fast synthesis for AHLs employed. No AHLs have been found in the cyanobacterial species tested, neither by Chromobacterium violaceum CV026 nor by Escherichia coli HB101 pUCD607 bioassay. No changes in dry weight or microcystin concentration were observed in M. aeruginosa PCC7820 grown in the presence of the AHL N-hexanoyl-DL-homoserine lactone. The activity of the spent medium of O. agardhii CYA29 was retained when it was heated up to 100°C for 20 min, frozen or freeze-dried. Molecular weight cut-off filtration showed the active compound to be less than 1 kD in size. The active component could not be extracted by dichloromethane or methanol, and activity was lost upon acidification. A small peptide of five amino acid moieties was isolated from an active fraction of the spent medium, four of which have been identified by 1H NMR to be serine, glycine, alanine, and the modified serine(thiazole). To my knowledge this is the first report of serine(thiazole) in natural products and the first thiazole containing peptide from O. agardhii.

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"January 2003" / Amendments in pocket inside back cover. / Bibliography: leaves 212-229. / xi, 229 leaves : ill. (some col.), map, plates (col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, Discipline of Environmental Biology, 2003

Reservoirs are the main drinking water sources in Taiwan. However, about half of 23 reservoirs suffer the eutrophication problems based on the calculated Carlson¡¦s TSI indexes for them. Thus, the reservoir water is seriously polluted. Chen-Ching Lake Reservoir, Fengshan Reservoir, and A-Kong-Tien Reservoir are three major reservoirs that supply water for the domestic, industrial, and agricultural uses in the Kaohsiung area. Due to the long-term sediment deposition at A-Kong-Tien Reservoir, a sediment dredge system is under construction at this reservoir. Thus, only Chen-Ching Lake Reservoir and Fengshan Reservoir play the most important roles in water supply at this moment. However, both Chen-Ching Lake Reservoir and Fengshan Reservoir are in the list of the most eutrophized reservoirs. There are several ways to evaluate the status of eutrophication of reservoirs. The single-index method and multi-variable modeling method are two of the most commonly methods for water quality analysis and eutrophication evaluation for the reservoirs in Taiwan. Based on the analytical results from previous studies, eutrophication results in the fast growing of seaweeds and they spread and cover the whole water bodies, which is called algal bloom. The type of seaweed causing eutrophication in Taiwan reservoirs are mainly Cyanobacteria, especially the commonly found Microcystis. They can not only cause some foul smells but release toxins into the water bodies. That endangers the safety of drinking water and affects the normal water usage. To prevent eutrophication, the nutrients loadings outside and inside of the reservoir areas must be reduced and controlled, which can effectively prohibit the growth of seaweeds. An air-pumping system can also be built for the same purpose. Regular water quality inspection should be carried out to monitor the fluctuation of water quality.