Fermentation process development of bioethanol by Zymomonas mobilis subsp. mobilis ATCC29191

• Main Authors: Tzu-Chieh Wong, 翁子傑
• Other Authors: 魏毓宏
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/12791494828442437541

碩士 === 元智大學 === 生物科技與工程研究所 === 95 === Zymomonas mobilis is a fermentative bacterium which can produce ethanol and carbon dioxide as major products. The major metabolic pathway in Zymomonas is Enter-Doudoroff pathway (ED pathway). When using glucose as the only carbon source, Zymomonas produced 1 mole of ATP and 1.87 mole of ethanol. When comparing to yeast, the earlier studies have demonstrated that Zymomonas is a better ethanol fermentative organism, such as the glucose uptake rate, high conversion rate, and no oxygen controlling. In continuous fermentation, Zymomonas can maintain the high conversion rate and the unit of ethanol production could reach 200 g/h. In this study, in order to promote the ethanol production and ethanol tolerance of Zymomonas mobilis subspecies mobilis ATCC 29191, growth factors, medium constituents, and some gene transformation should be discussed. Zymomonas is an oxygen tolerant bacterium but it is sensitive to the dissolved oxygen when growing in high concentration of glucose. In this study, Zymomonas grows at 30 ℃ and pH 5 without shaking. It is important to maintain the pH value. The conversion rate of ethanol could reach 75.83 mg/L when growing in 150 g/L of glucose. The inoculum has no effect on growth and ethanol production. For ethanol production, glucose, fructose, and sucrose are better carbon sources. Although earlier study have show, that Zymomonas can grow in 40 % of glucose, the data in this study shows different. The maximum tolerance of glucose concentration in medium is 25 %, and the conversion of ethanol is 98.31 g/L. According to the result of cell growth and ethanol production, tryptone and yeast extract are better nitrogen source. Cation shows no effect on growth and ethanol production. In order to manipulate DNA, finding out a useful vector is very important. Some references show that pRK415 may be the useful vector for DNA transformation. We construct pRHB-1(pRK415+phbCAB) from pBHR68 and pRK415 by using EcoRI and HindIII restriction enzyme site. After transformation, the plasmid seems to be successfully inserted into Z. mobilis subsp. mobilis ATCC 29191 but some data show that the plasmid in Zymomonas was not as stable as we thought. Some of the transforments lost the plasmid after inoculating couple of times and the result need to be further discussed.