| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 93 === Effects of various substrates and fermentation conditions, cell growth and accumulation of polyhydroxyalkanoates (PHAs) were investigated using 250 ml shake flasks and a 5 L fermentor. The strain used was Haloferax mediterranei.
It was found that the higher the concentrations of NaCl , MgSO4 and MgCl2 , the faster the cell growth and the lower the amount of PHA produced. The cells grew better by using yeast extract as nitrogen source compared to the inorganic nitrogen sources, and PHA accumulation didn’t enhance under nitrogen limitation.
The cells grew fastest at pH 6.5. The effect of temperature on cell growth and PHA accumulation was remarkable. PHA production can be stimulated by raising the temperature. The amount of PHA accumulated and PHA content obtained were 0.64 g/L and 16.6 % dry weight, respectively at 52 ℃ which was higher than the 0.06 g/L and 0.88 % obtained at 37 ℃. However, cell mass concentration was lowered as temperature increased. Cell mass concentration at 37 ℃ and 52 ℃ were 8.8 g/L and 5.3 g/L, respectively. To alleviate suppression of cell growth and increase the amount of PHA produced, we proposed a two-step temperature control strategy. At first stage, temperature was controlled at 37 ℃ to enhance cell mass proliferation, and then adjusted to 52 ℃ in the second stage to stimulate the accumulation of PHA. It was found that this strategy was effective to improve the amount of PHA accumulation without suppression of cell growth. Cell mass concentration, amount of PHA produced and PHA content were 12.4 g/L, 2.44 g/L and 20.4 % dry weight, respectively by using this strategy. The results obtained were higher than those under temperature controlled at 52 ℃ throughout. Besides, cell concentration and amount of PHA accumulation can be improved by pH-stat fed-batch operation. The results were 23.23 g/L and 4.66 g/L, respectively.
|
|---|
