Study On Pristinamycins Immobilized Fermentation And The Integrated Fermentation-seperation Process By Streptomyces Pristinaespiralis

Pristinamycins, a member of streptogramin family of antibiotics, is produced by Streptomyces pristinaespiralis. As it has a strong antibacterial activity against most gram-positive bacteria including vancomycin-resistant Entewcoccus, pristinamycins is considered as the preferred medicament against stubborn gram-positive bacterial infections.To increase the productivity and efficiency of pristinamycins fermentation, this work introduced the technology of immobilized fermentation. Thorough and systematic study of immobilized fermentation conditions and semi-batch fermentation was then conducted. Moreover, process model of in situ-adsorption of pristinamycin in fermentation is also developed.After control experiment, polyurethane foam was chosen as the preferred carrier for Streptomyces pristinaespiralis immobilization. Single-factor experiment indicated that both broth viscosity and pristinamycins productivity decreased with the increase of the carrier amount, while both broth viscosity and pristinamycins productivity increased with the delay of carrier adding. Then carrier amount (8xlcmxlcmxlcm) and adding time (24h after inoculation) was determined upon the foregoing result.In order to prove the beneficial effect brought by oscillatory temperature, orthogonal design was used to perform fermentation with oscillatory temperature. The result showed that a better temperature controlling strategy is 28℃during 0—36h, 23℃during 36-72h, and 25℃during 72-84h.The immobilized fermentation conditions were optimized by statistical methods based on Response Surface Method. Main factor levels after optimization were as follows: loaded volume of seed medium 29.4mL in 250mL flask, loaded volume of production medium 28.8mL in 250mL flask, shaker speed for seed incubation 204rpm. Under those conditions, average pristinamycins productivity can reach 230.2 mg/L, which is nearly consistent with the calculated one.The exploration of pristinamycins production by semi-batch fermentation was conducted. Three kinds of culture mediums with different component levels were used as production medium for semi-batch fermentations, while proper feeding and temperature control strategy was adopted. The results proved favorable reuse characteristics of the immobilized mycelium.A kinetic model for pristinamycin production and the film-pore diffusion model (FPDM) were combined together to describe the ISPR process carried out in a 2.5 L stirred tank bioreactor. Model parameters including pristinamycin formation rate constant, product inhibition constant, the film mass transfer coefficient and pore diffusion coefficient were determined with nonlinear least squares method. The theoretical calculations indicated that the model was in a good agreement with the practical ISPR process. The effect of the amount and the size of the resin on the ISPR results was studied, and the results indicated that the performance got better with the decrease of the resin size as well as with the increase of the resin amount in a certain range.