Formation of chloramphenicol resistant (CMr) spontaneous and nitroso-ethyl-urea-induced mutants of S.erythraea, an organism producing erythromycin, was studied. The mutants differed by the level of the chloramphenicol resistance (10 to 40 micrograms/ml). Part of the chloramphenicol resistance mutations had a pleiotropic pattern. 63.8 per cent of the CMr mutants was characterized by the growth thermosensitivity and 18.9 per cent was characterized by the absence of the melanin production property. The antibiotic potency of 56 per cent of the CMr mutants was higher than that of the initial strain. In some of the CMr mutants the property of resistance to other antibiotics was changed. A higher resistance of some mutants to chloramphenicol correlated with their increased lincomycin resistance. It was shown that chloramphenicol induced resistance to kanamycin in S.erythraea 5. Such a property for the resistance induction was preserved in the spontaneous low CMr mutants while the high CMr mutants isolated after the culture exposure to the mutagen lacked it. The CMr S.erythraea phenotype was genetically instable. Two different amplifying DNA sequences (18 and 70-78 kb in size) were detected in the CMr mutant genome. The chloramphenicol resistance mutation was localized in the S.erythraea chromosome region restricted by markers ura1 and met1.
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