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To overproduce endoxylanase from a recombinant Bacillus subtilis harboring the pJHKJ4 plasmid, the effects of carbon and nitrogen sources on the cell growth and expression level of endoxylanase were investigated in the flask cultures. Among the various carbon and nitrogen sources tested, glucose and maltose as carbon source and yeast extract as nitrogen source were found to be the most effective for the cell growth and the endoxylanase expression. When the concentration of glucose was increased from 0.5% to 5%, the highest activity of extracellular endoxylanse, 166 unit/㎖, was observed at 2% glucose. In case of maltose, the endoxylanase was stably produced at the level of 180 unit/㎖, regardless of the concentration of maltose. The higher the concentration of yeast extract, the greater cell growth and endoxylanase expression were obtained. However, the highest endoxylanase activity per unit cell mass was observed with 1% yeast extract. With the optimized medium (2% glucose, 1% yeast extract, etc), about 630 unit/㎖ of endoxylanse was expressed through the batch fermentation in a fermentor, which expression level corresponded to about 0.7 g-endoxylanase protein /ℓ. It was also found that the plasmid was stably maintained above 70% level, and more than 90% of endoxylanase activity was detected in the extracellular medium.
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