Researchers identified a 60 kb chromosomal region in Pseudomonas fluorescens NCIB 10586 required for pseudomonic acid (mupirocin) biosynthesis, a polyketide antibiotic that inhibits isoleucyl-tRNA synthetase. Using transposon mutagenesis with Tn5 and Tn1725 insertion mutants, they isolated 13 non-producing mutants and mapped seven Tn5 insertions within a clustered 55 kb region. The remaining insertions mapped to separate chromosomal locations, suggesting multiple regions are involved in biosynthesis. Through DNA sequencing and cloning of overlapping genomic fragments, the researchers identified genomic DNA extending over 60 kb containing the biosynthetic genes. Gene disruption experiments confirmed that genes throughout the 24 kb region between two key mutations (mup-33 and mup-210), and extending at least 13 kb further, are involved in pseudomonic acid production. The organization of these biosynthetic genes suggests similarity to polyketide synthase gene clusters found in other organisms.

Key findings

• A 60 kb chromosomal region was identified as necessary for pseudomonic acid biosynthesis in P. fluorescens
• Seven Tn5 insertions clustered within a 55 kb region, with additional mutations mapping to at least three other chromosomal locations
• The main biosynthetic gene cluster extends at least 24 kb between mutations mup-33 and mup-210, with genes also present 13 kb beyond mup-33
• Genes involved in the synthesis are distributed across multiple chromosomal regions rather than in a single continuous cluster
• Gene disruption analysis confirmed genes throughout the identified region are essential for producing pseudomonic acid