| Summary: | 碩士 === 輔仁大學 === 生命科學系碩士班 === 100 === Surfactants for industrial sectors are indispensably required. However, chemical-based surfactants have quite limited applications due to their biological toxicity, ecological concerns and narrow spectra of physicochemical characterization. It has been many years that microorganisms were proven to have great potential to produce various kinds of surfactants. Biosurfactants with biocompatibility from microorganisms demonstrated with more wider physicochemical characterizations and applications in industries. Therefore, exploiting microbial strains and the production technology of surfactants in the bio-industries has been one of the most important tasks. Here, the study mainly aimed to isolate a yeast strain with a high ability of producing biosurfactants and optimize their production. Screening by using drop crapes method and anthrone test, strain DS-18 was isolated from the sediment of Danshuei estuary located on the northwestern coast in Taiwan, and able to produce surfactants. Based on the analyses of SEM, physiological and biochemical characterizations, and rRNA sequences (including D1/D2 regions of 26S rRNA and ITS (internal transcribed spacer of rRNA genes)) DS-18 was closely related to basidiomycetous yeast Pseudozyma hubeiensis. HPLC, TLC, and NMR indicated that DS-18 can synthesize mannosylerythritol lipids (MELs)-like glycolipid surfactants. Investigated on the growth factors and conditions, DS-18 was showed with the better production of glycolipids at a sole carbon source of glucose, nitrogen source of NaNO3, growth temperature of 25℃, 17.5% of NaCl, 200 rpm shaking, and starting pH value 5. The optimal production of glycolipids in DS-18 was studied by the experimental design of response surface methodology (RSM), and presented with the highest yield of 78.25 g/L at the conditions of 8.5% glucose, 4% soybean oil, 0.2% NaNO3, 0.25% yeast extract, 0.01% MgSO4 and 0.01 % KH2PO4 in the shake flasks. This yield value is approximately 2.8-fold glycolipids produced than 28.17 g/L before medium optimization by RSM. The study suggested that yeast strain DS-18 possesses the great potential in the massive production of glycolipid surfactants. The further study on fermentative processes of glycolipid production by DS-18 in a fermentor will be carried out in the next stage in order to meet the industrial application.
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