已知空氣中存在微藻，但這方面的研究並未被重視。由於微藻主要生長於水中或潮濕環境，乾燥的空中是一種逆境。經歷這樣逆境仍能存活的微藻，其生理生化特性應能提供足夠的耐受性（tolerance），使細胞能夠忍受逆境，待細胞接觸到合適環境再生長繁殖。透過風力傳播到遠處，微藻可擴散自己的族群。本研究在東沙環礁國家公園於空氣中採集到四種微藻，由ITS1-ITS2 序列比對親緣關係及掃描式電子顯微鏡觀察結果，分別將這四種微藻命名為Scenedesmus sp.DSA1、Coelastrella sp. DSA2、Coelastrella sp. DSA3、Desmodesmus sp. DSA6。後續實驗證實，這些空飄微藻具有較高的抗乾旱、抗紫外線、耐高溫之能力，以及在高鹽逆境中產生抗氧化色素的機制。另外，這些微藻可以在50 ℃的溫度下存活，且能在高鹽逆境中產生類胡蘿蔔素，使藻液呈現橘紅色，其中包含蝦紅素、adonirubin、葉黃素、角黃素等。類胡蘿蔔素以DSA2、DSA3 產量較高，DSA1次之，DSA6 最少。經過HPLC 分析後發現產生的類胡蘿蔔素包含，蝦紅素（astaxanthin）、角黃（canthaxanthin）、beta胡蘿蔔素（beta-carotene）等。因此這幾株微藻可能具備商業價值或者能夠作為genetic resources。

It has been reported that microalgae can be found in the air, but aerial microalgae have not been investigated seriously. Microalgae lives in watery and moist environments. When dispersed in the air, these cells have to tolerate drought stress, UV radiation, and either high or low temperature in order to survive. For the cells that can survive these environmental stresses, they have a chance to quickly expand their habitats by using wind as a means to spread. To investigate what microalgal species can survive these stresses and what mechanisms they use, four new species of aerial microalgae were isolated on Dongsha Island in South China Sea in the seasonal northeast wind. Based on 18S rDNA and ITS sequences and morphological analyses, the four new species were named Scenedesmus sp. DSA1, Coelastrella sp. DSA2, Coelastrella sp. DSA3 and Desmodesmus sp. DSA6, which are members in the family Scenedesmaceae. Their tolerance to environmental stresses were assessed, and the potential mechanisms were studied. The cell wall thickness of the four species and two controls positively correlates to their UV tolerance. The tolerance to drought and low temperature of DSA1, DSA2 and DSA3 is extremely high. Freeze-drying (lyophilization) could not kill these cells, and this phenomenon could not be explained by water content in the dried cells or their antioxidation capacities in these cells. Thermotolerance of DSA1, DSA2 and DSA6 is among the highest in the literature. These cells in liquid culture could survive at 50 ℃. The carotenoid levels in the stressed DSA2 and DSA3 cells were higher than in the DSA1 cells, followed by that in the DSA6 cells. These carotenoids contained astaxanthin, adonirubin, lutein,canthaxanthin, and -carotene analyzed by using HPLC.

學位論文審定書
致　　謝 i
摘　　要 ii
Abstract iii
目　　錄 iv

一、前言 1
二、材料與方法 4
　2.1 微藻採集及標準養殖方法 4
　2.2 微藻之電子顯微鏡影像 4
　2.3 細胞壁厚度測定 5
　2.4 細胞壁自發螢光（Autofluorescence）影像 5
　2.5 DNA 萃取 6
　2.6 聚合酶鏈鎖反應（Polymerase Chain Reaction, PCR） 6
　2.7 定序及序列分析 9
　2.8 葉綠素含量分析 9
　2.9 微藻細胞塗盤 9
　2.11 紫外線逆境處理 10
　2.12 乾旱逆境處理 10
　2.13 海水逆境處理11
　2.14 高鹽逆境處理加速類胡蘿蔔素合成..11
　2.15 乾旱微藻細胞含水量測試 12
　2.16 微藻色素萃取 12
　2.17 高效液相層析（High Performance Liquid Chromatography, HPLC） 12
　2.18 抗氧化力測定 13
三、結果與討論 14
　3.1 微藻的採集 14
　3.2 微藻的鑑定 14
　3.3 微藻在乾旱逆境下的測試 15
　3.4 乾燥微藻含水量測定 16
　3.5 微藻在紫外線照射下的測試 16
　3.6 微藻細胞壁測試 17
　3.7 微藻在高溫下的葉綠素含量測試 17
　3.8 海水逆境 18
　3.9 高鹽逆境及色素含量分析 18
　3.10 抗氧化力測定 19
四、結論 20
五、圖表 23
六、參考文獻 40

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