Expression of chloramphenicol resistance specified by plasmid pHY416 hosted in Corynebacterium glutamicum

Chloramphenicol (Cm)-resistant colonies of Corynebacterium glutamicum strain AS019 hosting plasmid pHY416 occurred at a frequency of 4×10-7 when this strain, which normally expresses kanamycin (Km) resistance only, was placed under positive selection. These isolates produced a chloramphenicol acetyltransferase (CAT) and were tenfold more resistant to Cm than the parent strain. Resistance was lost in the absence of Cm selection but could be reselected from Km-resistant clones by reapplying Cm selection. Restriction endonuclease analyses of plasmids extracted from Cm-sensitive and-resistant strains indicated that expression of CAT activity corresponded to a loss of 0.9 kb of DNA from plasmid pHY416. © 1986 Springer-Verlag New York Inc.