3 ml of each of the seed culture broths was inoculated to a 250-ml baffled conical flask containing 30 ml of a main culture medium [a medium comprising 50 g of glucose, 20 g of ammonium sulfate, 0.5 g of potassium dihydrogen phosphate, 0.5 g of dipotassium hydrogen phosphate, 2 g of urea, 0.5 g of magnesium sulfate heptahydrate, 2 mg of iron sulfate heptahydrate, 2.5 mg of manganese sulfate pentahydrate, 1 mg of thiamin hydrochloride, 100 μg of biotin, and 30 g of calcium carbonate, contained in 1 L of water, sterilized and then adjusted to pH 7.0 with sulfuric acid], and cultured under the conditions of 30° C. and 220 rpm for 16 hours.
