Protective Effects of Cryoprotectants and Lyoprotectants on the Survival of Persipeptide Producing Streptomyces zagrosensis UTMC 1154.

Abstract

Streptomyces sp. are bacteria recognized as the producers of more than half of the known bioactive compounds. Developing appropriate preservation methods for industrial strains of Streptomyces is necessary, as continuous subculture could have significant negative effects on their characteristics, including their potential to produce secondary metabolites. The effects of two common preservation methods on a bioactive metabolite producer, Streptomyces zagrosensis UTMC 1154, were studied. In the cryopreservation method, glycerol and dimethyl sulfoxide (DMSO) were evaluated as cryoprotectants. Three different suspending fluids including skimmed milk, sucrose+gelatin and Mist. dessicans were compared as the freeze-drying methods. Freeze-dried samples were stored at 4°C for 6 months and at 37°C for 1 and 2 weeks in an accelerated storage stability study, which approximately correspond to storage at 4°C for 10 and 20 years, respectively. Frozen samples were stored at -20°C, -70°C and in the vapor phase of liquid nitrogen for 6 months. Skimmed milk and DMSO were the most efficient protectants for survival and functional maintenance of the strain during the lyophilization and cryopreservation processes (p < 0.05), respectively. The survival rate of S. zagrosensis was 95.0% and 99.3% after 6 months of preservation by using skimmed milk as lyoprotectant and DMSO as the cryoprotectant, respectively. The obtained results showed that cryopreservation is the method of choice for long-term preservation of S. zagrosensis. Cryopreservation also led to only 1%-3% reduction in the biological activity of the strain after 6 months preservation in vapor phase of the liquid nitrogen.