Chloramphenicol resistance in Streptomyces coelicolor A3(2): Possible involvement of a transposable element

Summary The transfer of a Chl element, causing resistance to chloramphenicol in Streptomyces coelicolor A3(2), was studied in NF x SCP1^– superfertile crosses. When the Chl element is on the donor side (NF) its transfer to the recombinant cells was virtually total as if the element acted as a second concomitant transfer origin. When the Chl element was on the recipient side (SCP1^–) it was never displaced by the immigrant chromosome even when the region facing chl ⁺ was selected for. A fraction of the original Chl^– mutants presented a requirement for arginine (ArgB^–). A Chl^– mutant gave rise spontaneously to ArgB^– derivatives at high frequency. The same ArgB^– requirement come out at high frequency among Chl^– derivatives from a cross NFChl^– x SCP1^–Chl⁺ in which neither parent required arginine or produced spontaneously arginineless derivatives. It is suggested that the Chl element is a transposable element (Tn) presumably associated with insertion sequences (IS). The insertional inactivation of the Chl element may be accompanied or followed by a deletion in the adjacent ArgB gene.