Enhanced Production of the Fluorinated Nucleoside Antibiotic Nucleocidin by a rif^{\scale70%\text{R}}-Resistant Mutant of Streptomyces calvus IFO13200

Nucleocidin, a fairly broad antibacterial and trypanocidal agent produced by Streptomyces calvus, has the unique structure of 40-fluoro-50-O-sulfamoyl adenosine. This nucleoside antibiotic has been a target for organic synthesis in past decades; however, microbial large-scale production has not been established due to low yield and poor reproducibility. To activate the dormant secondary metabolism of S. calvus, we examined the effect of an rpoB mutation that was induced by ultraviolet light irradiation. The resulting rifampicinresistant strains showed remarkably improved antibiotic activity, which was extracted by n-butanol and identified by Electron-Spray-Ionization Mass Spectrometry. DNA sequencing identified double mutations, C1309A and C1318A, in the rpoB gene (according to the numbering of Streptomyces coelicolor rpoB). The resulting amino acid substitutions, H437N and R440S, corresponded to two of the previously reported amino acid substitutions that allowed the activation of dormant actinorhodin production in S. lividans 66.