| Bacterial cellulose(BC) is a kind of polysaccharose produced by microorganism. It’s wildly applied in the field of food ingredient, paper industry, cosmetics, medical material for its excellent physical and chemical properties. At present, low yield of BC, which is one of the main obstacle for large-scale production and application. Therefore optimization of strain production process is one important route for improving BC yield. Gluconacetobacter xylinus receive much concern for its outstanding productivity. It’s reported that different strains of Gluconacetobacter xylinus have different physiological and biochemical characteristics. This study chose four G xylinus strains held by lab(DHU-ATCC-1 〠DHU-ZCY-1 〠DHU-ZGD-1 〠DHU-YQ-1)and G xylinus strain ATCC23770 to comparison of static culture, mechanical agitation culture and preservation condition optimization.The major results of the dissertation are summarized as follows:1. Differences exist in the static culture with various starting conditions for five G xylinus, and conditions(mainly starting pH and nutrition medium) affect the differences. We find the following conclusion: Effect of nutrition medium to rough dry weight appear greater. Impact trend of nutrition medium to G xylinus strains are almost same, but differences are not the same when in different starting pH. Terminal pH shows little connection to starting pH, but medium have vary effects on them. Change in the rough dry weight: DHU-ZGD-1 have the highest of all but affect largely from medium. DHU-ZCY-1 and DHU-YQ-1 follow behind but largely affected by starting pH. The rank of the rough dry weight is: DHU-ZGD-1>DHU-YQ-1>ATCC23770> DHU-ZCY-1>DHU-ATCC-1. Sugat content part: DHU-ZGD-1 is at the top but unstable. DHU-ATCC-1 and DHU-YQ-1 affects largely from medium. The Rank of the sugar content are: DHU-ZGD-1>DHU-ATCC-1>DHU-YQ-1> ATCC-23770 >DHU-ZCY-1.Terminal pH link to starting pH and no connection to medium.Therefore,DHU-ZGD-1is more suitable in static culture.2. Comparison of G xylinus’ s mechanical agitation culture results.The fermentation processes of the strains are the same: in the first two days pH and DO descend sharply, then to certain value; sugar content decline slowly at first then sharply. However, DHU-ZGD-1have several differences: DO value decline one day later compare to others, pH value changes slowly, sugar content maintains in the high level. Rough dry weight of DHU-ZGD-1 is the highest among the strains, DHU-ZCY-1 is the next, other three hold in the close level. All in all,DHU-ATCC-1is more suitable for mechanical agitation culture.3. Comparison of preservation results for five G xylinusVariation tendency of-20℃ and-80℃ group are basic agreed: Rough dry weight and sugar of all strains decline before week 2, terminal pH value rise to some extent. After week 2, Rough dry weight become rise and stable, as well as sugar content and terminal pH. The differences are as follows: pH value of each time nodes changes more fiercely in-80℃ group, sugar content of-80℃ group is lower than-20℃ group, difference between G xylinus strain is smaller in-80℃ group.Effects of several protective agents to G xylinus strains are different. Sucrose and lactose group in HS medium is unstable than normal medium, but other four are on the contrary. ATCC23770 in lactose and DMSO differs largely than others. Overall consideration, trehalose, skim milk and glycerol are more suitable as protective agent for G xylinus. |
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