海洋微藻由於具有許多有益的成分，例如：多元不飽和脂肪酸、蛋白質、類胡蘿蔔素和多醣體，因此奠定了其應用價值。在諸多種微藻中，擬球藻是一種富含脂質的藻種，在適當的培養條件下其總脂質含?可高達總微藻乾重的68% (w/w)，因此其於實際應用中展現了極大的潛力。為了提升擬球藻的商業應用性，在本研究中我們嘗試以聚乙二醇來提升微藻的生物質與脂質的生產效益。首先，我們使用0 ~ 5% (w/v)的PEG-6000評估聚乙二醇的濃度對於微藻生長率的改變。接著測試不同的聚乙二醇分子量其範圍為400到20000對於微藻的生長、細胞尺寸以及生物質、脂質與EPA產量的影響。此外，為了評估將聚乙二醇應用於大規模的密閉式培養系統中的可行性，我們更進一步測試聚乙二醇降低氧氣抑制對於微藻生長的能力。研究結果顯示，在聚乙二醇所產生的滲透壓範圍2.465 ~ 2.472 MPa內能夠提升微藻的生長。在相同濃度0.5% (w/v)下，較高分子量的聚乙二醇分子展現出較高的生物質與脂質的總生產力。在本研究中所設定的各種不同條件下，0.5% (w/v)的PEG-20000不會干擾細胞尺寸且能夠在培養7天後使生物質、總脂質量與總EPA產量提高50%以上，為擬球藻培養提供了最佳的條件。另外我們發現0.5% (w/v)的PEG-20000能夠能夠減少氧氣抑制對於微藻生長的影響，綜合以上的實驗結果，本研究提出以PEG-20000為介導的微藻培養方式對於實際產業的應用具有高度的潛力。 The value of marine microalgae has long been identified due to their useful products such as polyunsaturated fatty acids, proteins, carotenoids, and polysaccharides. Among various microalgae, Nannochloropsis oculata is a lipid-rich species which can yield up to 68% (w/w) total lipid under appropriate cultivation and thus exhibit high potential for practical applications. To enhance the commercial availability of Nannochloropsis oculata, effectiveness of using polyethylene glycol (PEG) to increase microalgal biomass and lipid production was investigated. We first examined the effects of PEG concentrations on microalgal growth using 0 - 5% (w/v) PEG-6000, and followed by exploring the effects of PEG molecule weights range from 400 to 20000 on microalgal growth, size, as well as on yields of biomass, lipids, and eicosapentaenoic acid. Furthermore, the capacity of PEG to reduce the effect of oxygen inhibition on microalgal growth was also studied in order to assess the adaptability of PEG for use in large-scale and closed setting. Our results showed that PEG-induced osmotic stress in the range of 2.465 - 2.472 MPa can increase microalgal growth. The PEG with higher molecular weight exhibited higher biomass but less lipid productivity under equal concentration of 0.5% (w/v). Among different conditions set in this study, 0.5% (w/v) PEG-20000 enabled to yeld > 50% (w/w) increases in biomass, total lipid and eicosapentaenoic acid amounts after seven days without interference of cellular size, offering the optimal condition for Nannochloropsis oculata cultivation. With another fact that 0.5% (w/v) PEG-20000 enabled to diminish the effect of oxygen inhibition on microalgal growth, the PEG-20000-mediated microalgal cultivation exhibits a high potential for use in industry.
