ABSTRACTStreptomyces iranensisHM 35 is an alternative rapamycin producer toStreptomyces rapamycinicus. Targeted genetic modification of rapamycin-producing actinomycetes is a powerful tool for the directed production of rapamycin derivatives, and it has also revealed some key features of the molecular biology of rapamycin formation inS. rapamycinicus.The approach depends upon efficient conjugational plasmid transfer fromEscherichia colitoStreptomyces, and the failure of this step has frustrated its application toStreptomyces iranensisHM 35. Here, by systematically optimizing the process of conjugational plasmid transfer, including screening of various media, and by defining optimal temperatures and concentrations of antibiotics and Ca2+ions in the conjugation media, we have achieved exconjugant formation for each of a series of gene deletions inS. iranensisHM 35. Among them wererapK, which generates the starter unit for rapamycin biosynthesis, andhutF, encoding a histidine catabolizing enzyme. The protocol that we have developed may allow efficient generation of targeted gene knockout mutants ofStreptomycesspecies that are genetically difficult to manipulate.IMPORTANCEThe developed protocol of conjugational plasmid transfer fromEscherichia colitoStreptomyces iranensismay allow efficient generation of targeted gene knockout mutants of other genetically difficult to manipulate, but valuable,Streptomycesspecies.
Draft Genome Sequences of Salmonella Lysozyme Gene Knockout Mutants