The Effect Of Dissolved Oxygen And Addition Of Antibiotic On Curdlan Fermentation

Curdlan is an extra-polysaccharide produced by Alcaligenes faecalis. The intracellular nucleotides play a very important role in metabolic maintenance and curdlan production. For example, ATP, ADP and so on provide the energy of curdlan biosynthesis. And the UDP-glucose exists as a crucial precursor substance in the process of curdlan biosynthesis. In this work, the effect of dissolved oxygen on the curldlan biosynthesis in terms of intracellular nucleotides level is analysed. And a two-stage DO fermentation model of curdlan biosynthesis phase is build in the basis of different curdlan biosynthesis rate in different fermentation phase. The effect of addition of ammonia and antibiotics in combination on intracellular nucleotides and key enzyme of curdlan biosynthesis also the curdlan production rate is investigated too.A quantitative method for determining the ATP, ADP, AMP, UTP, UDP, UMP, NADH, NAD+, and UDP-glucose in Alcaligenes faecalis by reversed phase ion pair chromatography (IP-RP-HPLC) was proposed. The method proved to be reproducible. The method provides a sound basis for determining the cellular nucleotides change and oxidation-reduction state throughout the curdlan fermentation, and thus the relationship between curdlan biosynthesis and intracellular nucleotides could be explored.The conclusion that the change of the level of intracellular nucleotides have three turning points as increase in DO is taken by the research of the intracellular nucleotides change in different DO state. The three turning points of 10%, 40% and 60% can divide the environment of bacterium into four DO state from low to high by step: anaerobic, aerobic, sufficient oxygen and oxygen excess. And energy efficiency rather than the substrate supply is the major constraint for the enhancement of curdlan production. So the appropriate DO state can be predicted to the value of about 60%. The subsequent experiment prove the prediction. And a two-stage DO fermentation model for curdlan biosynthesis phase is build in the basis of different curdlan biosynthesis rate in different fermentation phase to decrease the energy consumption.The effect of different antibiotics on the biomass and curdlan biosynthesis is investigated. The experiment demonstrates the addition of antibiotics only have no influence on the curdlan biosynthesis. But the addition of ammonia water and antibiotic in combination have a very significant effect on curdlan biosynthesis. And the addition of ammonia water and antibiotic in combination increase the level the intracellular nucleotides and key enzyme of curdlan biosynthesis. This phenomena illuminate that the ammonia stimulate the renewal of some key enzyme and the precursor substance of curdlan biosynthesis and increase the glucose metabolic flux to curdlan biosynthesis when the antibiotic inhibit the cell growth.