Strain improvement by combined UV mutagenesis and ribosome engineering and subsequent fermentation optimization for...

The bleomycins (BLMs) are important clinical drugs extensively used in combination chemotherapy for the treatment of various cancers. Dose-dependent lung toxicity and the development of drug resistance have restricted their wide applications. 6'-Deoxy-BLM Z, a recently engineered BLM analogue with improved antitumor activity, has the potential to be developed into the next-generation BLM anticancer drug. However, its low titer in the recombinant strain Streptomyces flavoviridis SB9026 has hampered current efforts, which require sufficient compound, to pursue preclinical studies and subsequent clinical development. Here, we report the strain improvement by combined UV mutagenesis and ribosome engineering, as well as the fermentation optimization, for enhanced 6'-deoxy-BLM production. A high producer, named S. flavoviridis G-4F12, was successfully isolated, producing 6'-deoxy-BLM at above 70 mg/L under the optimized fermentation conditions, representing a sevenfold increase in comparison with that of the original producer. These findings demonstrated the effectiveness of combined empirical breeding methods in strain improvement and set the stage for sustainable production of 6'-deoxy-BLM via pilot-scale microbial fermentation.