Scaling up a virginiamycin production by a high-yield Streptomyces virginiae VKM Ac-2738D strain using adsorbing resin addition and fed-batch fermentation under controlled conditions

Virginiamycin produced by Streptomyces virginiae as a natural mix of macrocyclic peptidolactones M and S is widely used in the industrial production of ethanol fuel and as an antibiotic feed additive for cattle and poultry. Its main antimicrobial components, M1 and S1 factors, act synergistically if the M1:S1 ratio in the final product is 70-75:25-30. This fact significantly complicates the development of stable high-yield strains suitable for industrial application. In the previous work, authors obtained a mutant S. virginiae VKM Ac-2738D strain, characterized by a high productivity in flasks and the optimum M1:S1 ratio (75:25) in the final product. In this study, the scale-up of the virginiamycin production by VKM AC-2738D from shake flasks to a pilot-scale (100 L) stirred fermentor was carried out and the possibility of the in situ use of synthetic adsorbing resins to remove virginiamycin from culture broth was assessed. After the optimization of pH and dissolved oxygen concentration (6.8-7.0 and 50%, respectively), the fed-batch fermentation of VKM Ac-2738D with continuous addition of 50% sucrose solution (5 g/L/day starting from 48 h of fermentation) resulted in a final virginiamycin titer of 4.9 g/L. Among four tested resins, Diaion^® HP21 added to fermentation medium prior to sterilization absorbed 98.5% of the total virginiamycin that simplifies its further recovery procedure and increased its total titer to 5.6 g/L at the M1:S1 ratio of 74:26. The developed technology has several important advantages, which include (1) the optimum M1:S1 ratio in the final product, (2) the possibility to use sucrose as a carbon source instead of traditionally used and more expensive glucose or D-maltose, and (3) selective binding of up to 98.5% of produced virginiamycin on the adsorbing resin.