Improvement of pristinamycin-producing Streptomyces pristinaespiralis by rational screening

Screening and selection of lovastatin hyper-producing mutants of Aspergillus terreus using cyclic mutagenesis

134 fungal cultures isolated from different soil samples were screened for lovastatin production. Of these, 38 isolates produced different levels of lovastatin. An Aspergillus terreus strain GD13, producing 190 mg/l of lovastatin was selected and subjected to a rational mutation-selection programme based on the resistance to lovastatin and fatty acid synthase (FAS) inhibitors, viz., iodoacetamide and N-ethylmaleimide. After three cycles of mutagenesis, a hyper-producing mutant (EM19) exhibiting 7.5-fold (1424 mg/l) higher levels of lovastatin when compared to wild type parent strain was obtained.

Enhanced production of spinosad in Saccharopolyspora spinosa by genome shuffling

Spinosad (spinosyns A and D) is a mixture of secondary metabolites produced by Saccharopolyspora spinosa. It is used in agriculture as a potent insect control agent with exceptional safety to non-target organisms. In this study, we applied genome shuffling of S. spinosa to achieve a rapid improvement of spinosad production. Ten strains with subtle improvements in spinosad production were obtained from the populations generated by the mutation with nitrosoguanidine and ultraviolet irradiation, and then they were subjected for recursive protoplast fusion. After four rounds of genome shuffling, a high yielding strain, designated as S. spinosa 4-7, was successfully isolated. Its production reached 547 mg/L, which was increased by 200.55% and 436.27% in comparison with that of the highest parent strain and the original strain, respectively. The subculture experiments indicated that the high producer of S. spinosa 4-7 was stable. Spinosad fermentation experiments by S. spinosa 4-7 were carried out in a 5-L fermentor, and its production of spinosad reached 428 mg/L after 168 h of fermentation.

Medium optimization based on statistical methodologies for pristinamycins production by Streptomyces pristinaespiralis

The optimization of nutrient levels for the production of pristinamycins by Streptomyces pristinaespiralis CGMCC 0957 in submerged fermentation was carried out using the statistical methodologies based on the Plackett-Burman design, the steepest ascent method, and the central composite design (CCD). First, the Plackett-Burman design was applied to evaluate the influence of related nutrients in the medium. Soluble starch and MgSO4 x 7H2O were then identified as the most significant nutrients with a confidence level of 99%. Subsequently, the concentrations of the two nutrients were further optimized using response surface methodology of CCD, together with the steepest ascent method. Accordingly, a second-order polynomial regression model was finally fitted to the experimental data. By solving the regression equation from the model and analyzing the response surface, the optimal levels for soluble starch and MgSO4 x 7H2O were determined as 20.95 and 5.67g/L, respectively. Under the optimized medium, the yield of pristinamycins in the shake flask and 5-L bioreactor could reach 1.30 and 1.01 g/L, respectively, which is the highest yield reported in literature to date.