極端嗜鹽菌體迴流與連續式醱酵生產聚羥基烷酯之研究

THE STUDY OF POLYHYDROXYALKANOATES PRODUCTION BY Haloferax mediterranei IN CELL-RECYCLING AND CONTINUOUS CULTIVATION

劉凱銘(Kai-Ming Liu)

指導教授 ： 陳志成

大同大學/工程學院/生物工程學系所/碩士(2008年)

摘要

為了降低對石油的依賴以及因濫用石化塑膠而對自然環境所造成的傷害，減少石化塑膠的使用，並開發物化性質與機械性質皆類似石化塑膠之替代材料已刻不容緩。已知極端嗜鹽古生菌Haloferax mediterranei，能於體內累積具有與石化塑膠相似性質之生物可分解性聚羥基烷酯 (polyhydroxyalknoates, PHA)。目前PHA生產成本仍然偏高，而欲降低其成本須仰賴生產過程中提升菌體濃度與採用長期連續醱酵的方式。但是在長期培養的情況下，亦必須移除菌體代謝之抑制性物質的累積，以避免菌體生長之減緩或菌體老化。本研究發現，在連續式培養生產PHA，而以葡萄糖和酵母萃取物分別做為碳、氮源之饋料，在稀釋速率為0.025 h-1的培養過程中，菌體濃度和高分子含量分別可維持在24 g/l和27 %，PHA體積產率為0.162 gL-1h-1。而利用陶瓷過濾膜濾除代謝性抑制物質與進行細胞迴流連續培養生產PHA，在稀釋速率為0.028 h-1的培養過程中，菌體濃度和高分子含量分別可維持在35 g/l和22 %，PHA體積產率0.215 gL-1h-1，但易發生過濾膜為高黏度菌體堵塞現象不利長期培養。而以碳氮源獨立饋料之醱酵策略進行細胞迴流與連續醱酵生產PHA，發現可得到菌體濃度40 g/l和高分子含量54 %，PHA體積產率為0.216 gL-1h-1，且可縮短菌體達到最高濃度的時間，與維持醱酵液內較低的氨氮濃度 (3 g/L以下) ，而有助於菌體生長、PHA生產，且不易造成過濾膜堵塞而有利可長時間醱酵。另外以米糠玉米澱粉和酵母萃取物獨立饋料進行細胞迴流與連續式醱酵則可獲得菌體濃度47 g/l和高分子含量45 %與PHA體積產率為0.212 g L-1 h-1，且可長期穩定生產PHA。

關鍵字

嗜鹽菌 ； 聚羥基烷酯 ； 細胞迴流

並列摘要

In order to decrease the demand of petroleum, and also to reduce the pollution problem caused by misusing of petroleum-based plastic, it is urgent to develop a substitutive plastic that has the similar physical-chemical and mechanical properties as the petroleum-based plastic. It is known that the extremely halophilic Archaea, Haloferax mediterranei, can accumulate biodegradable polyhydroxyalknoates (PHA) of similar properties as petroleum-based plastic. But, the production cost of PHA is expensive. In order to increase the productivity of PHA, it need to increase cell concentration during a long-term continuous fermentation, meanwhile, we also need to reduce the accumulation of inhibitive metabolites that will damage the cell growth and also the yield of PHA. In this study, by using a continuous cultivation of dilution rate at 0.025 h-1, and also by feeding glucose and yeast extract at fixed ratio we obtained the cell concentration and PHA content at 24 g/l and 27 % respectively, and the volumetric productivity of PHA was 0.162 gL-1h-1. By using a cell recycling continuous cultivation with ceramic filter membrane at the dilution rate of 0.028 h-1, the cell concentration and the PHA content could be maintained at 35 g/l and 22 % respectively, and the volumetric productivity of PHA was 0.215 gL-1h-1, but there was a problem of filter blocking by the viscous cell mass. If we preceded cell recycling and continuous fermentation by feeding carbon and nitrogen sources independently, the cell concentration of 40 g/l and PHA content of 54 % could be obtained, and the PHA volumetric productivity could reach 0.216 gL-1h-1; in such operation, we can keep low ammonia concentration (below 3 g/l), that will facilitate cells growth, better PHA content and also without filter blocking by viscous cell. By utilizing extruded rice bran (ERB) and extruded cornstarch (ECS) as carbon sources to produce PHA, we could obtain the cell concentration of 47 g/l, PHA content of 45 % and the PHA volumetric productivity of 0.212 gL-1h-1 in the cell recycling and continuous cultivation by feeding carbon and nitrogen sources independently.

並列關鍵字

Haloferax mediterranei ； polyhydroxyalkanoate ； cell-recycle

參考文獻

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