Factors affecting the production and molecular weight of levan of Bacillus subtilis natto in batch and fed-batch culture in fermenter

• This is the first systematic production of levan in fermenter by B. subtilis natto.
• This is the most efficient levan production reported to date.
• Pulsed feeding of sucrose enhanced the levan production significantly.
• Sucrose concentration is the most effective factor controlling the size of the levan.
• Levans of different molecular sizes can be tailor-made to meet various applications.

The production of levan in batch and fed-batch culture of Bacillus subtilis (natto) Takahashi in fermenter was investigated. Efficient and high yield levan production (61 g/L at 24 h; 3.4 g/L/h) was obtained when the bacteria were cultured in medium containing sucrose (250 g/L) at pH 7.0, temperature 37 °C and agitation speed 175 rpm; in addition, pulsed feeding of sucrose enhanced the levan production significantly to 100 g/L (1.7 fold increase). This is the first systematic study of this strain in fermenter and the most efficient levan production reported to date. The yield and molecular weight of levan were strictly dependent on the reaction conditions. Sucrose concentration was the most effective factor controlling the molecular weight of the synthesized levan, this leads to tailor made levans of different molecular sizes for applications of different purposes.