| Summary: | 碩士 === 南臺科技大學 === 生物科技系 === 106 === As the aquaculture industry expands and intensification of the breeding environment continues, water quality is emerging as one of the key factors in the breeding environment. The main causes of deterioration and pollution of water quality in culture ponds are considered to be ammonia nitrogen, nitrous acid and nitrates. These substances, which easily lead to odour, eutrophication and insufficient dissolved oxygen in the water, affect the survival rates of fish and shrimp. In order to solve problems associated with water quality, many auxiliaries have been developed, including feed additives, probiotics, and biological agents, the usage of which has shown an increasing trend. These products may achieve water purification using safe, non-toxic, green, and sustainable concepts. At present, the use of nitrifying bacteria is limited. Therefore this study focused on using certain characteristics of microorganisms to improve water quality, and successfully screened two strains, BSWC11 and BS155, with relatively good water purification capabilities. The degradation of ammonia nitrogen, nitrous acid, and nitrate by BSWC11 and BS155 were investigated. Ammonia nitrogen, nitrous acid, and nitrate were rapidly degraded within 48 hours; and the concentrations of ammonia nitrogen, nitrous acid and nitrate decreased to safe values within 120 hours. The strains were analysed using 16s rRNA gene sequence alignment and were found to belong to species of the genus Bacillus. These were Gram-positive strains that are generally recognized as safe (GRAS). To optimize the yield of these strains, the Plackett-Burman (PB) design was used to identify two key media followed by Central Composition Design (CCD) for media optimization. Finally, a fermentation tank was used to develop scale cultivation for strain amplification. Our study indicates that these two new strains may potentially replace nitrifying bacteria, in the search for new water purification products for the aquaculture industry.
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