Study On Fermentation Of Ethanol By Zymomonas Mobilis And Its Metabolic Flux Distribution Analysis

According to the strain fermentation engineering and metabolic engineering theory, a Zymomonas mobilis was systematically studied in this thesis, including the screening of best antioxidant, studying the effects of antioxidants on growth and metabolism under oxidative stress, building the metabolic network and its modle, study the effect of temperature and pH conditions on the enzyme activity of the glucose metalolism, especially researching the effects of different dissolved oxygen and pH conditions on the ability of the antioxidant stress, metabolic flux analysis under the antioxidant.1. Studying the effects of diverse antioxidants on growth and metabolismunder oxidative stress, it was found that pyrocatechol was more useful for growth and ethanol fermentation of Z. mobilis, and improving anti-oxidation stress ability. The optimized conditions obtained by orthogonal experiment were as follows, pH 5,200 ml liquid volume,100 rpm shaker frequency and 0.1 mg/ml pyrocatechol concentration. The maximum ethanol yield could reach 40.71 g/L under the optimized condition.2. Researching the different dissolved oxygen and pH conditions on the antioxidant stress indicators including DPPH, hydroxyl radical, superoxide anion and malondialdehyde, the results show that free radical scavenging capacity has increased and decreased lipid peroxides under the antioxidant, it was more useful for growth and ethanol fermentation of Z. mobilis.3. By analyzing the distribution of the metabolic flux in different dissolved oxygen and pH values conditions. The distributions of the metabolic flux in ED, EMP, and TCA were different in kinds of conditions. With the decrease of pH values the fluxes of ethanol, malic acid and succinic acid delined deeply and the consumption rate of the total glucose decreased progressively; it was found that pyrocatechol was more useful for improving anti-oxidation stress ability and metabolic fluxes of the pyruvate, succinic acid and ethanol; the pyruvic acid was considered as the key nodes in the metabolism of Z.mobilis, the distribution flux in this node influence the yield of ethanol. Therefore, it is important to control pH and dissolved oxygen in fermentation.4. Zymomonas mobilis is used to study the effect of different pH conditions on the enzyme activity of the glucose metalolism. The results showed that The optimum of pH was 5.0～5.5. Metabolic enzyme activities of intracellular which belong to the pathway flowing to ethanol (glycolysis way, ED paths etc) in metabolic network strengthen and most conducive to glycolysis way toward the development of ethanol direction within the pH5.0-5.5.