Abstract

El-Tayeb, O.M. , Salama A.A., Hussein, M.M.M. ,and El-Sedawy, H.F.

Optimization of the fermentation process using the gene amplified variant of Amycolatopsis mediterranei, NCH, in the fermentation medium F2 was carried out by the application of fed-batch regime. The addition of 12% glucose alone at day 4 or simultaneously with 0.1% yeast extract at day 2 led to an increase in the yield of rifamycin B by 46% and 57%, respectively. The application of fed-batch regime together with replacing (NH4)2SO4 with the better yielding inorganic nitrogen sources NH4NO3 or KNO3 (F2m1 and F2m2 media, respectively) increased the production of rifamycin B. The use of F2m1 medium alone or with an additional 12% glucose added at day 4 increased the yield by 53% and 120%, respectively. However, further addition of 0.1% yeast extract led to an increase in the yield by only 63%. The addition of 3% soytone or 0.05% NH4NO3 to F2m1 at day 3 increased the yield by 72% and 61%, respectively, compared to productivity in F2 medium. The use of F2m2 medium increased the yield by 50%. The addition of 12% glucose at day 4 or of 0.1% yeast extract at day 2 to F2m2 medium led to an increase in the yield by 119 and 55%, respectively, compared to F2 medium. However, when both 12% glucose and 0.1% yeast extract were added at similar scheduled times only 64% increase in the yield occurred. By applying the three most effective optimization regimes determined using variant NCH with F2m2 medium on a standard rifamycin B producing strain, Nocardia mediterranei ATCC 21789, a similar pattern of increase in the antibiotic yield was observed. Thus, the use of F2m2 instead of F2 medium either alone or with an additional 12% glucose added at day 4 increased the yield by 36 and 75%, respectively, whereas the addition of 0.1% yeast extract to F2 medium increased the yield by 15%. In conclusion, the application of fed-batch technique with the optimum modifications of the medium constituents increased rifamycin B production by variant NCH to a maximum of 17.17 g/l compared to a yield of 5.3 g/l by the tested standard strain under the same conditions. The increase in rifamycin B production using the standard strain confirms the usefulness of the tested medium modifications in the improvement of rifamycin B production and its possible application in fermentations using other rifamycin B producer strains and also shows the superiority of variant NCH as a producer, when compared to the standard strain.