Uncovering the Effects of Ammonium Sulfate on Neomycin B Biosynthesis in Streptomyces fradiae SF-2

The aminoglycoside antibiotic neomycin has broad antibacterial properties and is widely used in medicine and agriculture. With the discovery of neomycin’s potential applications in treating tumors and SARS-CoV-2, it is necessary to accelerate the biosynthesis of neomycin. In the present study, we investigated the effects of various inorganic salts on neomycin B (the main active neomycin) biosynthesis in Streptomyces fradiae SF-2. We found that 60 mM (NH4)2SO4 could promote neomycin B biosynthesis and cell growth most effectively. Further comparative transcriptomic analyses revealed that 60 mM (NH4)2SO4 inhibited the EMP and TCA cycles and enhanced the expression of neo genes involved in the neomycin B biosynthesis pathway. Finally, a neomycin B potency of 17,399 U/mL in shaking flasks was achieved by overexpressing neoE and adding 60 mM (NH4)2SO4, corresponding to a 51.2% increase compared with the control S. fradiae SF-2. In the present study, the mechanism by which (NH4)2SO4 affects neomycin biosynthesis was revealed through transcriptomics, providing a reference for the further metabolic engineering of S. fradiae SF-2 for neomycin B production.