Effects of S-adenosylmethionine on AfsKRS regulation in pristinamycin biosynthesis in Streptomyces pristinaespiralis.

In Streptomyces pristinaespiralis, AfsKRS system has differential regulation for PI and PII component biosynthesis of pristinamycin, but it is unknown whether S-adenosylmethionine (SAM) plays an important role in the AfsK-AfsR-AfsS signal transduction cascade during pristinamycin production. The possible target of exogenous SAM in the AfsKRS system and the biological role of SAM during the production of PI and PII were investigated using three mutantsΔafsK,ΔafsR andΔafsS defective in signal cascade pathway of AfsKRS. It was found that external SAM had a significant activation of PI production (1.85-fold increase) but had no obvious effect on PII production in the original strain F618 with the normal response of AfsKRS regulation. Addition of SAM resulted in a similar increase in pristinamycin yield in the mutant with defective afsK or afsR, but induced more crucial activation of PI biosynthesis than PII biosynthesis both in ΔafsK (1.65-fold and 1.15-fold increase respectively) and ΔafsR (1.27-fold and 1.09-fold increase respectively). Exogenous SAM only significantly enhanced PII production in ΔafsS (1.1-fold increase). These results could provide valuable insights into the regulatory function of the AfsKRS system in S. pristinaespiralis.

Optimization of fermentation conditions for pristinamycin production by immobilized Streptomyces pristinaespiralis using response surface methodology

Response surface methodology was used to optimize the fermentation conditions for the production of pristinamycin by immobilization of Streptomyces pristinaespiralis F213 in shaking flask cultivation. Seed medium volume, fermentation medium volume and shaking speed of seed culture were found to have significant effects on pristinamycin production by the Plackett-Burman design. The steepest ascent method was adopted to approach the vicinity of optimum space, followed by central composite design for further optimization. A quadratic model was built to fit the pristinamycin production. The optimum conditions were found to be seed medium volume of 29.5 ml, fermentation medium volume of 28.8 ml, and shaking speed of seed culture at 204 rpm. At the optimum conditions, a production of 213 mg/l was obtained, which was in agreement with the maximum predicted pristinamycin yield of 209 mg/l. This is the first report on pristinamycins production by immobilized S. pristinaespiralis using response surface methodology.