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

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 arginine-less 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.