Diazaquinomycin Biosynthetic Gene Clusters from Marine and Freshwater Actinomycetes.

Tuberculosis is an infectious disease of global concern. Members of the diazaquinomycin (DAQ) class of natural products have shown potent and selective activity against drug-resistant Mycobacterium tuberculosis. However， poor solubility has prevented further development of this compound class. Understanding DAQ biosynthesis may provide a viable route for the generation of derivatives with improved properties. We have sequenced the genomes of two actinomycete bacteria that produce distinct DAQ derivatives. While software tools for automated biosynthetic gene cluster (BGC) prediction failed to detect DAQ BGCs， comparative genomics using MAUVE alignment led to the identification of putative BGCs in the marine Streptomyces sp. F001 and in the freshwater Micromonospora sp. B006. Deletion of the identified daq BGC in strain B006 using CRISPR-Cas9 genome editing abolished DAQ production， providing experimental evidence for BGC assignment. A complete model for DAQ biosynthesis is proposed based on the genes identified. Insufficient knowledge of natural product biosynthesis is one of the major challenges of productive genome mining approaches. The results reported here fill a gap in knowledge regarding the genetic basis for the biosynthesis of DAQ antibiotics. Moreover， identification of the daq BGC shall enable future generations of improved derivatives using biosynthetic methods.