Enhancement of neomycin production by engineering the entire biosynthetic gene cluster and feeding key precursors in Streptomyces fradiae CGMCC 4.576.

Neomycin, an aminoglycoside antibiotic, is widely used in the livestock husbandry due to its higher antimicrobial activity and availability of feed additives in animals. However, its production yield is relatively low and cannot meet the needs of developing market and clinical application. Here, the entire natural neo cluster was cloned from Streptomyces fradiae CGMCC 4.576 by φBT1 integrase-mediated site-specific recombination. Then, the rational reconstruction of the neo cluster was performed by using λ-Red-mediated PCR targeting for improving neomycin production. In order to coordinate with this attempt, the supplementation of suitable precursors was carried out. The constructed recombinant strain Sf/pKCZ03 has multi-copy of the neo cluster modified by disrupting the negative regulatory gene neoI and replacing the native promoter of the neoE-D with PkasO*. Compared to the yield (1282 mg/L) of Streptomyces fradiae CGMCC 4.576, the engineered strain Sf/pKCZ03 had a 36% enhancement of neomycin production. Quantitative real-time PCR analysis revealed the increased transcription of structural genes (neoE, neoB, neoL, aacC8) and regulatory genes (neoR, neoH) in Sf/pKCZ03. Additionally, under the supplementation of 1 g/L N-acetyl-D-glucosamine and 5 g/L L-glutamine, the yield of engineered strain Sf/pKCZ03 showed 62% and 107% improvements compared to that of the wild-type strain in the original medium, respectively. These findings demonstrated that engineering the antibiotic gene cluster in combination with precursors feeding was an effective approach for strain improvement, and would be potentially extended to other Streptomyces for large-scale production of commercialized antibiotics.