Abstract
Thirty-three strains of Bacillus subtilis were isolated from commercially available “natto” preparations. These strains produced significantly different amounts of the viscous material, levan. Levan production by some strains depended on the cultivation conditions. Levan production reached a maximum after 8 days of cultivation, the optimum temperature and pH ranging from 25°C to 30°C and from 5 to 8, respectively. Sucrose was the most suitable carbon source and levan production increased in parallel with the initial sucrose concentration. The optimum biotin concentration was 10μg%. Levan was fractionated into two parts with a high and a low molecular weight. The average molecular weight of the low-molecular-weight fraction varied among strains. No difference in levan sucrase activity in the culture broth was found among strains.
