title: Extrachromosomal DNA in chloramphenicol resistant myxococcus strains.
abstract: The presence of extrachromosomal DNA in strains of Myxococcus xanthus and M fulvus was examined by rate-zonal centrifugation of radioactively-labelled DNA in 'cleared lysates'. All the strains examined contained extrachromosomal DNA, with the exception of M. xanthus FBt. Chloramphenicol resistance is inducible in M. xanthus FBt. A peak of extrachromosomal DNA, containing covalently closed molecules, was found in one of the induced strains, implying that induction of chloramphenicol resistance is associated with the production of a plasmid. By incubating R+ strains of Escherichia coli with myxococci, R factor-mediated chloramphenicol resistance can be introduced into the latter. Evidence of extra chromosomal DNA in a derivative of M. xanthus with chloramphenicol resistance from R factor RI. 19 unique to the chloramphenicol strain, was obtained. By using a double-labelling technique, several chloramphenicol-resistant strains of M. fulvus M were examined. Evidence for a peak, unique for the chloramphenicol-resistant strain, was found in a strain with resistance derived from the R factor, S-a, but not from comparable strains with resistance derived from R factors R57b, R1. 19 and R478.
mesh_terms: D002701:Chloramphenicol / Q000494:pharmacology*; D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000032:analysis*; D004270:DNA, Circular / Q000032:analysis*; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects; D005111:Extrachromosomal Inheritance; D009154:Mutation; D009231:Myxococcales / Q000032:analysis* / Q000187:drug effects; D011815:R Factors
chemical_list: D004269:DNA, Bacterial; D004270:DNA, Circular; D002701:Chloramphenicol