Influence of agitation speed on production of curdlan by Agrobacterium species

Influence of dissolved oxygen level on production of curdlan by Agrobacterium species was investigated. Preliminary shake flask experiments showed that both cell growth and curdlan production were higher at a smaller volume of medium (50-100 ml in 500 ml flasks). As culture volume increased from 100 ml to 300 ml, both cell concentration and curdlan production decreased, indicating that higher oxygen transfer is required for a higher production of curdlan. Time profiles of cell concentration and curdlan production in a 5-liter jar fermentation at different agitation speeds, ranging from 300 rpm to 700 rpm, supported the fact of higher production of curdlan at higher oxygen transfer rate observed in shake flask cultures. At a higher agitation speed (600 rpm), the highest curdlan production (64.4 g/l) was obtained in 120 h of a batch fermentation. However, curdlan production was not improved at the higher agitation speed (700 rpm). For the mass production of curdlan, fermentation was performed in a 300-liter fermenter under the condition where the same volumetric oxygen transfer coefficient was obtained as in 5-liter jar fermentation. As high as 9.28 kg of curdlan with a final concentration of 58 g/l was obtained in 120 h batch cultivation, enlarging the potential in the industrial production of curdlan.