Researchers in New Brunswick Scientific's in-house labs have developed a unique control strategy to achieve high antibiotic expression levels in a pilot-scale fermentation process of Streptomyces hygroscopicus. Using the BioFlo 6000 fermentor's on-line controller with touchscreen interface augmented by the powerful supervisory capabilities of AFSBioCommand software, scientists were successful in optimizing the culture environment for rapamycin production. Harvested dry cell weight recovered from the 100 liter fermentor was over 25 grams/L; intracellular rapamycin production was over 110 milligrams/L; and fermentation time was reduced by almost a day to 120 hours.
Streptomyces expresses a variety of secondary metabolites, such as rapamycin, which are used in medical and biological applications. During fermentation, dense mycelia are produced, which are highly variable in phenotype and especially susceptible to changing conditions during cultivation. Formation of secondary metabolites is usually favored by sub-optimal cell growth conditions. Nutrient transfer problems can restrict the metabolism of the culture, and a high oxygen transfer rate (OTR) is always required. Therefore, it was necessary to develop a fermentation protocol which allowed for initial cell growth to a sufficient density as to facilitate the production of large quantities of the antibiotic, while preventing the culture from becoming so dense as to interfere with its ability to obtain vital nutrients and oxygen for the production of rapamycin.
Materials and Methods
Seed inoculum of Streptomyces hygroscopicus NBS-9746, selected from ATCC 29253 cell strain, was cultured in an Innova 4300 incubator shaker, then transferred to a 10 L BioFlo IV bench fermentor, and fina