The effects of viscosity and aeration rate on rapamycin production in an airlift bioreactor by using Streptomyces hygroscopicus

• An increase in viscosity by adding carboxymethylcellulose (CMC) could reduce pellet size.
• Using an airlift bioreactor instead of an agitation tank can avoid the break-down of pellets.
• The application of both viscosity control and an airlift bioreactor has great potential.

The production of antibiotics by filamentous organisms is often dependent on the morphology and pellet size within the culture. An increase in viscosity by adding carboxymethylcellulose (CMC) could reduce pellet size and increase rapamycin production in the cultivation of Streptomyces hygroscopicus. A maximum yield of 410 mg/L of rapamycin was obtained when 3 g/L of CMC was added to a 5 L agitation bioreactor, as compared to 260 mg/L in the control batch (without the addition of CMC). Using an airlift bioreactor instead of an agitation tank can avoid the break-down of pellets due to the high shear force with the latter. The results indicate that an aeration rate of 1.5 vvm could achieve the maximum rapamycin production of 543 mg/L in an airlift bioreactor with 3 g/L of CMC adding. The application of both viscosity control and an airlift bioreactor has great potential with regard to commercialized rapamycin production.