溫度變化對 Ralstonia eutropha 在限磷條件下饋料批次 發酵生合成 PHB 之探討

Effect of Temperature on the Biosynthesis of Poly-β-Hydroxybutyrate by Ralstonia eutropha under Phosphorus-Limited Batch Fermentation

聚-β-羥基丁酸酯（poly-β-hydroxybutyrate, PHB）是生物可分解聚合物可用以替代石化塑膠 降低環境汙染。本研究以 Ralstonia eutropha（ATCC 17699）為實驗菌株，於 5 L 之發酵槽進行 不同溫度（26、30 及 35℃）限磷條件饋料批次發酵培養，探討菌體量、PHB、淨菌體量之生 合成量，葡萄糖、氮源及磷源之消耗率，並比較三種溫度之菌體與 PHB 產率、基質消耗率及 產率係數。不同溫度培養，以 30℃培養之葡萄糖消耗率較高，因而菌體量、PHB 生合成量、 淨菌體量較高。氮源消耗率隨培養溫度升高而下降，顯示 R. eutropha 於較低溫或較高溫生長會 受抑制，進而影響菌體量、PHB 生合成量、淨菌體量。30℃ 培養菌體量產率最高 0.74 g/L‧h， 淨菌體量產率最高 0.25 g/L‧h，PHB 產率最高 0.57 g/L‧h。不同培養溫度 26、30 及 35℃，其 菌體量產率分別可達 0.45、0.74 和 0.63 g/L‧h，PHB 產率分別可達 0.35、0.57 和 0.50 g/L‧h。 YP/X（PHB yield coefficient on biomass）於 30℃培養最大值為 0.79。YR/G（residual biomass yield coefficient on glucose）於三種不同溫度培養，YR/G最大值分別為 0.23、0.17 和 0.23。YR/N（residual biomass yield coefficient on nitrogen）於三種不同溫度培養，YR/N最大值分別為 7.28、7.12 和 6.10。 實驗結果顯示，30℃饋料批次發酵培養 R. eutropha 具有較高的菌體量、PHB 和淨菌體量的產 率，且其 YP/X產率係數亦以 30℃培養較佳。

Poly-β-hydroxybutyrate （PHB）is a biodegradable polymer that can substitute petroleum-based plastics. Ralstonia eutropha（ATCC 17699）was cultivated in a 5-L fermentation tank at different temperatures（26, 30, and 35°C）under phosphorus-limited batch fermentation. The biosynthetic rates of biomass, PHB, and residual biomass and the consumption rates of glucose, nitrogen source, and phosphorus source were measured. The productivities of biomass and PHB and the consumption rate of the matrix and yield coefficients at the three temperatures were compared and studied. The glucose consumption rate was highest at 30 °C, and this temperature yielded a higher production of biomass, PHB, and residual biomass. The nitrogen consumption rate decreased with increasing culture temperature. R. eutropha growth was inhibited at lower or higher temperatures, which in turn affected PHB biosynthesis and the yields of biomass and residual biomass. Cultivation at 30°C yielded the highest productivities of biomass, residual biomass, and PHB（ 0.74, 0.25, and 0.57 g/L/h, respectively）. At 26, 30, and 35°C, the productivities of biomass were 0.45, 0.74, and 0.63 g/L/h and of PHB were 0.35, 0.57, and 0.50 g/L/h, respectively. The maximum value of the PHB yield coefficient for biomass was 0.79, at a temperature of 30°C. The residual biomass yield coefficient for glucose was 0.23, 0.17, and 0.23, at 26, 30, and 35°C, respectively. The residual biomass yield coefficient for nitrogen was 7.28, 7.12, and 6.10 at 26, 30, and 35°C, respectively. The experimental results indicated that the batch fermentation of R. eutropha at 30°C produced the highest bacterial biomass, residual biomass, and PHB yields and PHB yield coefficient of biomass.