利用Pseudomonas oleovorans生產具中長碳鏈之PHA

Abstract

本研究採用Pseudomonas oleovorans菌株發酵生產生物可分解性高分子，由於此菌株可合成出具中長碳鏈的PHA，性質較柔韌有彈性，與支鏈上短鏈長的PHB相較之下更具應用性。目前PHB已被大量生產，而具中長碳鏈之PHA(mcl-PHA, medium-chain-length PHA)由於產量低，仍未被加以探討，因此期望能夠提高mcl-PHA的產量。 使用辛酸鈉為碳源，硫酸銨為氮源，所產生的PHA為側鏈上具有五個碳的PHO(poly-3-hydroxyoctanoate)。發酵槽培養實驗中，當轉速提高時，溶氧量增加，使得菌體生長代謝加快，對數生長期提前結束。使用低溫培養，於16小時可得菌量4.43g/L，雖然菌量些微提升，但對於PHA累積量並沒有幫助。批次饋料培養，對數生長期延長，PHA產率降低。 錐形瓶饋加十一烯酸培養實驗，於培養40小時取樣可得最高菌量、最高PHA累積量分別為4.14g/L、2.148g/L，PHA含量可提升至51.8%。發酵槽饋加十一烯酸培養實驗，產物為PHO與PHU(poly-3-hydroxy-8-noneneoate為主)所形成之混摻物，且雙鍵所佔比例隨時間增加，培養第73小時可得到雙鍵比例37.39%；隨培養時間增加，玻璃轉移溫度(Tg, glass transition temperature)由-34.03℃下降至-42.40℃，顯示PHA性質變得更加柔韌具有彈性。

Biosynthesis of biodegradable PHA (polyhydroxyalkanoate) using Pseudomonas oleovorans was investigated. By using this microorganism, mclPHA can be synthesized. Comparing with sclPHA, the property of mclPHA is more flexible. To date only sclPHA have been synthesized at larger scale. Because of limited availability of the mclPHA, there are only a few reports on it. Different products of PHA were obtained by using different carbon sources. When using sodium octanoate as a sole carbon source, major product was PHO (poly(3-hydroxyoctanoate)). Dissolved oxygen increases with higher stirrer speed, which promote metabolism of microorganism, logarithmic curve will end earlier. Change cultivation time from 30℃ to 18℃ at 8 hr can obtain 4.43g biomass/L, although dry cell weight was increased by a little, PHA accumulation was still too low. With fed-batch cultivation, PHA productivity is much lower than batch culture. When feeding with undecylenic acid by flask culture, weight of PHA and PHA content were 2.148 g/L, 51.8% respectively. When feeding with undecylenic acid by fed-batch culture, there was a lag time when microorganism using undecylenic acid as a new carbon source. The molar fraction of unsaturated monomer could be achieved by 37.39% at 73 hr cultivation. We can see the property of PHA become flexible with cultivation time by the lower of Tg.