Cultivation of protocorms of Dendrobium candidum in air-lift bioreactors

Abstract

To explore the factors affecting the growth of protocorms of Dendrobium candidum and substance synthesis in a reactor, in order to provide a new method for mass production of raw materials of D. candidum. Protocorms in vitro were used as experimental materials to study the effect of inoculum volume, light intensity and air volume on the growth of protocorms of D. candidum and the accumulation of polysaccharide and dendrobine in a 3 L-air lift balloon type bioreactor. After 30 days of cultivation in a bioreactor, protocorms became dark green and grew well at the inoculum volume of 10 g x L(-1). The polysaccharide content in protocorms showed no difference at various inoculum volumes; whereas the dendrobine content showed differences (with the highest treatment at the inoculum volume of 10 g x L(-1)), particularly the productions of polysaccharide and alkaloid reached the maximum at the inoculum volume of 10 g x L(-1). The condition of 1 600 lx of light intensity was the most favorable for the growth of protocorms. Though light played a role of improving the accumulation of polysaccharide in protocorms of D. candidum, it could inhibit the accumulation of dendrobine. Polysaccharide content and production were better under light conditions of 1 600 and 2 400 lx than dark conditions. Despite the maximum dendrobine content in dark conditions, the dendrobine production showed the maximum in the light condition of 1 600 lx due to poor growth of protocorms. Protocorms grew well and became dark green at the air volume of 0.2 vvm (air volume culture volume per minute) , which was better than at 0.1 and 0.3, with maximum polysaccharide and dendrobine contents and productions. In a 3 L-air lift balloon type bioreactor with a working volume of 2 L, the conditions of 10 inoculum volume, 1 600 lx light intensity and 0.2 air volume were favorable for the growth of protocorms and the production of dendrobine. This demonstrates that the cultivation of D. candidum and substance synthesis in a reactor is an effectie approach for mass production of polysaccharide and dendrobine.