Effect of air flow rate on scleroglucan synthesis by Sclerotium glucanicum in an airlift bioreactor with an internal loop

The effect of air flow rate upon scleroglucan production in batch cultures of S. glucanicum NRRL 3006 cultivated in airlift reactor with internal loop was studied using air flow rates from 0.25 m(3)/h to 1.00 m(3)/h. Biomass formation was favoured at high air flow rates (with maximum biomass at 0.75 m(3)/h), whilst scleroglucan synthesis was highest at relatively low air flow rates (maximal at 0.40 m(3)/h). S. glucanicurn had a maximum specific growth rate of 0.018 h(-1) at 0.75 m(3)/h. The values of the key process optimisation parameters (scleroglucan yield, productivity and specific productivity) were all maximal at 0.4 m(3)/h. Since achievement of an adequate cell mass is essential for subsequent biopolymer synthesis, a bi-staged process was developed. In the first phase biomass formation was maximised by a high air flow rate of 0.75 m(3)/h, while in the second phase a lower air flow rate of 0.40 m(3)/h was used to stimulate biopolymer synthesis and minimise operational costs.