Production of rapamycin in Streptomyces hygroscopicus from glycerol-based media optimized by systemic methodology

Rapamycin, produced by the soil bacterium Streptomyces hygroscopicus, has the ability to suppress the immune system and is used as an antifungal, anti-inflammatory, antitumor, and immunosuppressive agent. In an attempt to increase the productivity of rapamycin, mutagenesis of wild-type Streptomyces hygroscopicus was performed using ultraviolet radiation, and the medium composition was optimized using glycerol (which is one of the cheapest starting substrates) by applying Plackett-Burman design and response surface methodology. Plackett-Burman design was used to analyze 14 medium constituents: M100 (maltodextrin), glycerol, soybean meal, soytone, yeast extract, (NH4)2SO4, L-lysine, KH2PO4, K2HPO4, NaCl, FeSO4·7H2O, CaCO3, 2-(N-morpholino) ethanesulfonic acid, and the initial pH level. Glycerol, soytone, yeast extract, and CaCO3 were analyzed to evaluate their effect on rapamycin production. The individual and interaction effects of the four selected variables were determined by Box-Behnken design, suggesting CaCO3, soytone, and yeast extract have negative effects, but glycerol was a positive factor to determine rapamycin productivity. Medium optimization using statistical design resulted in a 45% (220.7 ± 5.7 mg/l) increase in rapamycin production for the Streptomyces hygroscopicus mutant, compared with the unoptimized production medium (151.9 ± 22.6 mg/l), and nearly 588% compared with wildtype Streptomyces hygroscopicus (37.5 ± 2.8 mg/l). The change in pH showed that CaCO3 is a critical and negative factor for rapamycin production.