Production of rapamycin on agro-industrial substrates in benchtop bioreactor: Insights on process development and obstacles management

Rapamycin is a unique medication with an endless list of clinical bioactivities and special potency. One of the drawbacks restricting its widespread use was its relatively high price. The current study presents a pioneering production approach of rapamycin using costless agro-industrial by-products in a stirred-tank bioreactor, which is assumed to usher in a new era in the production, pricing, and distribution of rapamycin. A remarkable drop in rapamycin yield (≤0.81 mg/l) was recorded at the studied levels of agitation (100, 150 & 200 rpm). The clear signs of microbial growth and activity pointed to specific unfavorable conditions for rapamycin production in the fermentor. Cause analysis and basic differences between fermentations in a shaken-flask and fermentor were practically pursued, leading to valuable considerations about high working volume, oxygen availability, and shear stress in the fermentor. An interesting production of the drug (8.1 mg/l) after 72 hours was achieved at high agitation (600 rpm). Decreasing the aeration rate to 0.5v/v/m verified a daily productivity of 4.3 mg/l/day, which was surprisingly comparable to that in a flask (4.8 mg/l/day). The efficiency of different organic solvents in extracting rapamycin from cell debris and residues of natural substrates was clarified; ethanol for 60 minutes was the proper solvent and potentiated more than a 17% increase in the yield.