Optimization of fermentation medium for bitespiramycin production by response surface methodology

Objective To optimize the fermentation medium components for bitespiramycin production in a new gene-engineered bitespiramycin-producing strain with integrated double copy of isovaleryltransferase(ist)gene.Methods Response surface methodology(RSM)was adopted,two level fractional factorial design(FFD)was first used to evaluate the influence of six related factors.The path of steepest ascent was used to approach the optimal region of the fermentation conditions subsequently.The concentrations of those two main factors were further optimized by using central composite design(CCD).Results Two factors were determined to play important roles in the medium,which were KH2PO4 and NaCl.By solving the quadratic regression model equation,the optimal concentrations of the variables were determined as KH2PO4 0.645 g·L-1,NaCl 12.5 g·L-1.An optimized fermentation medium was obtained for this newly developed strain,which was composed of(g·L-1):starch 60,CaCO3 7.0,MgSO4 2.0,NH4NO3 6.0,yeast powder 3.0,fish meal 15,MnCl2 0.10,NaCl 12.5,KH2PO4 0.645.Under the optimum conditions,the relative bitespiramycin titer of 139% as predicted in theory and 142% in the experiment were obtained with an increase of 42% compared to the initial medium.Meanwhile the relative proportion of total isovalerylspiramycin was no significant changes.Conclusions Response surface methodology as a statistical tool is efficient to improve the productivity of a new gene-engineered strain of antibiotic producer.