限磷條件下添加葡萄糖與第二碳源丙酸鈉對連續式發酵生產PHB和PHBV之影響

Effect of the Addition of Glucose and Sodium Propionate as the Second Carbon Source on Continuous Production of Polyhydroxybutyrate and Poly-(hydroxybutyrate-co-hydroxyvalerate) under a Phosphorus-Limited Condition

本研究於限磷條件下，探討添加葡萄糖和第二碳源丙酸鈉於不同稀釋速率對Ralstonia eutropha菌體生質量、PHB（poly-hydroxybutyrate）、PHBV（poly-(hydroxybutyrateco-hydroxy-valerate)）生合成量及PHBV於菌體中含量之影響。以3L之發酵槽進行發酵培養，發酵初期採批次發酵培養，待菌體生長至對數生長期（exponential phase），轉換為連續式發酵培養。以葡萄糖為碳源之培養，降低稀釋速率，菌體生質量、PHB生合成量、PHB於菌體中含量有先增加而後減少的趨勢。菌體生質量以稀釋速率為0.101h-1達最高7.31g/L，PHB生合成量和PHB於菌體中含量以稀釋速率為0.151h-1達最高分別為1.97g/L和27.9%。葡萄糖平均消耗速率以稀釋速率為0.151h-1達最高3.04g/L·h，表示於此稀釋速率下，培養液提供足夠碳源以生合成菌體與PHB。稀釋速率再下降，饋料流速下降，碳源提供量減少，PHB生合成量及PHB於菌體中含量均降低。以葡萄糖為碳源並添加丙酸為第二碳源之培養，降低稀釋速率，菌體生質量、PHBV生合成量、PHBV於菌體中含量、HV（hydroxyvalerate）於PHBV中含量有先增加而後減少的趨勢。稀釋速率為0.0531h-1時，平均菌體生質量達最高6.70g/L。稀釋速率為0.0851h-1時，PHBV生合成量、PHBV於菌體中含量、HV於PHBV中含量達最高，分別為1.90g/L、29.4%、10.5%。菌體產率以稀釋速率為0.165h-1時達最高0.804g/L·h。HB（hydroxybutyrate）與PHBV產率以稀釋速率為0.0851h-1達最高，分別為0.145和0.162g/L·h。HB、HV和PHBV於淨菌體中含量，以稀釋速率為0.0851h-1時達最高，表示稀釋速率為0.0851h-1、饋料流速為110.7mL/h時，提供足夠碳源以合成HB和HV。稀釋速率下降為0.0531h-1時、饋料流速為69.0mL/h時，饋料流速較慢，無法提供足夠碳源以合成HB和HV，因而HB、HV、PHBV於淨菌體中含量下降。 This study investigated the effects of glucose and sodium propionate supplementation(as the second carbon source ) on the bacterial biomass, polyhydroxybutyrate ( PHB ) and poly- (hydroxybutyrate-co-hydroxyvalerate) (PHBV) synthesis, and PHBV content in Ralstonia eutropha under phosphorus-limited conditions. Fermentation was performed in a 3-L fermenter. Batch fermentation was conducted in the initial phase, followed by continuous fermentation in the exponential phase. In the culture containing glucose as the carbon source, the biomass of bacteria, the amount of PHB biosynthesis, and the content of PHB in cells initially increased and then decreased when the dilution rate was decreased. The highest biomass of 7.31 g/L was obtained at a dilution rate of 0.101 h -1 . The highest amount of PHB biosynthesis and the highest content of PHBV in cells were 1.97 g/L and 27.9%, respectively, which were obtained at a dilution rate of 0.151 h -1 . The highest average glucose consumption rate of 3.04 g/L·h obtained at a dilution rate of 0.151 h -1 provided adequate carbon content for microbial growth and PHB synthesis. A decrease in the dilution rate resulted in the reduction of the flow rate of feed, supply of the carbon source, amount of PHB biosynthesis, and content of PHB in bacteria. When glucose was used as the carbon source, sodium propionate was added as the second carbon source, and the dilution rate was reduced, the biomass, PHBV synthesis, PHBV content in cells, and hydroxyvalerate(HV) content in PHBV increased and then decreased. When the dilution rate was 0.0531 h-1 , the average biomass was 6.70 g/L. At a dilution rate of 0.0851 h-1 , the PHBV synthesis, PHBV content in cells, and HV content in PHBV were the highest(1.90 g/L, 29.4%, and 10.5%, respectively) . The cell yield coefficient was 0.804 g/L·h at a dilution rate of 0.165 h-1 . The yield coefficients of HB (hydroxybutyrate) and PHBV were the highest (0.145 and 0.162 g/L·h, respectively) at a dilution rate of 0.0851 h-1 . The contents of HB, HV, and PHBV in the residual biomass were the highest when the dilution rate was 0.0851 h-1 , indicating that a dilution rate of 0.0851 h-1 , a feed flow rate of 110.7 mL/h, and an adequate carbon source were provided to synthesize HB and HV. The low feed flow rate of 69.0 mL/h at a dilution rate of 0.0531 h-1 could not provide an adequate carbon content for the synthesis of HB and HV.