Crucial factor for increasing the conjugation frequency in Streptomyces netropsis SD-07 and other strains

Streptomyces netropsis SD-07, the producer of novel polyene macrolide antifungal antibiotics, was isolated from soil. For the investigation of the functions of its biosynthesis genes and regulation mechanisms, a genetic operating system is necessary. In this study, we successfully transferred the plasmid DNA of pSET152 from the methylation deficient donor, Escherichia coli ET12567/pSET152/pUZ8002, to S. netropsis SD-07 by conjugation and evaluated the crucial factors influencing the conjugation frequency. Ca(2+) ions in presence the conjugation media may increase the conjugation frequency by 1000-10 000 times than Ca(2+) ions absence in the same conjugation media, and 10-100 time higher than Mg(2+) ions. Similar results (increasing the conjugation frequency by 10-100 times when media containing 60 mM CaCl2 ) were also obtained from the conjugation between E. coli ET12567 and Streptomyces coelicolor, S. lavendulae, S. venezuelae, despite their conjugation media were different (MS, CM, GS). So, CaCl2 concentration is a crucial factor for increasing the conjugation frequency, and the suitable concentration may probably be 60 mM. In addition, synthetic medium containing a small amount of organic nitrogen source may benefit increasing the conjugation frequency. These findings could be valuable for the development of a practical method for achieving conjugation in other Streptomyces spp.