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In this study, we intended to increase mass production of Bacillus subtilis through medium
optimization by statistical experimental method. For the seed culture of B. subtilis, tryptic
soy broth and 15 hours were selected as the basic medium and inoculum age respectively.
Final dry cell weight and protease contents of B. subtilis by basic production medium were
1.8 g/L and 0.04 U/mL, respectively. First, maltose, yeast extract and potassium phosphate
dibasic were selected as carbon and nutrient sources for mass production of B. subtilis by
using one factor at a time method. And then Plackett-Burman experimental design was
used to determine the key factors which are critical to produce the biological products and
to culture the cell by fermentation. According to the result of Plackett-Burman experimental
design, key factors were selected yeast extract and Na2CO3. to obtain the optimum
concentrations of two selected variables the response surface methodology was performed .
The optimized medium composition found consisted of 20 g/L maltose, 18.5 g/L yeast
extract, 2 g/L K2HPO4, 0.36 g/L Na2CO3, 0.4g/L MgSO4 and 0.01g/L CaCl2. Dry cell weight (22.3 g/L) by optimum production medium were increased 12 times, as compared to those determined with basic production medium. Fermentation conditions were examined for the mass production of B. subtilis. The effect of temperature, agitation speed, pH and aeration rate on the mass production of B. subtilis were also observed in a batch fermenter which was carried out in a 2.5 L bioreactor with a working volume of 1.5 L containing optimized production medium. As a result, Dry cell weight of batch culture was 83.8 g/L at 37℃, 300 rpm, pH 7.0 and 3 vvm.