Enhanced rapamycin production through kinetic and purification studies by mutant strain of Streptomyces hygroscopicus NTG-30-27

Abstract

Research work was implemented to describe the kinetics of cell growth, substrate utilization and product formation using a mutant strain of Streptomyces hygroscopicus NTG-30-27 in a 3-L bioreactor under optimized condition. Various substrate inhibition mathematical models were applied and it was found that the cell growth and substrate utilization kinetic data fitted well to those models. Andrew’s kinetic model was fitted very well (R2 = 0.998) with our experimental data among different models tested for analysis whereas Luedeking–Piret model suggested that our product is mixed growth associated. The values for maximum specific growth rate (µmax), doubling time (td), saturation constant (KS), inhibition constant (KI) and yield coefficient (YX/S) were found to be 0.03985 h−1, 17.16 h, 2.076 g/l, 0.009 g/l and 0.290 g g−1. Final rapamycin yield with mutant strain was found to be 531.4 mg/l on its 5th day of fermentation which is 6.7-fold higher than the wild type (79.31 mg/l). The effect of aeration on rapamycin production was studied by batch fermentation in a stirred tank reactor (STR) using S. hygroscopicus NTG-30-27. Dynamic behaviour and aeration efficiency of the reactor, as well as rheology pattern of the fermentation broth, were determined by calculating volumetric mass transfer coefficient (KLa) of the process using “Dynamic gassing out method”. KLa was found to be 54.53 h−1 which is quite significant for rapamycin production. Further purification and structural analysis of the extracted sample were carried out by liquid chromatography–mass spectrophotometry (LC–MS) technique in positive ionization mode and molecular mass was found to be 936 D. Finally, 90.62% purified rapamycin was obtained from the study.