High frequency conjugal transfer of tylosin genes and amplifiable DNA in Streptomyces fradiae.

Genes encoding enzymes for tylosin biosynthesis, genes involved in the expression of resistance to tylosin (Tyl), hygromycin B (Hm), chloramphenicol (Cm), and mitomycin C (MC), and a single copy of an amplifiable unit of DNA (AUD) were jointly transferred at very high frequencies by conjugation from several different Streptomyces fradiae strains to S. fradiae JS85, a mutant defective in many or possibly all tylosin biosynthetic reactions and containing a multiple tandem reiteration of the AUD. No recombination was observed between nar, rif and spc genes in conjugal matings, but recombination was observed between these genes after protoplast fusion. Tylosin biosynthetic genes were transferred at a much lower frequency to S. fradiae JS87, another mutant defective in many or all tylosin biosynthetic reactions, but deleted for the AUD and other DNA sequences. These findings suggest that tylosin structural genes, several genes encoding antibiotic resistance determinants, and amplifiable DNA are present on a self-transmissible element that does not mobilize chromosomal genes, and that JS85 and JS87 contain deletions, and JS85 an amplification, of overlapping portions of this element.