Isolation and Partial Characterization of Four Plasmids from Antibiotic-resistant Thermophilic Bacilli

Abstract

Twenty-nine antibiotic-resistant isolates of thermophilic bacilli were examined for the presence of covalently closed circular duplex DNA molecules by agarose-gel electrophoresis and cesium chloride-ethidium bromide density gradient centrifugation. Five of the 29 strains tested contained covalently closed circular molecules. Two of the streptomycin-resistant strains contained the same 2 plasmids: pAB118A of MW 4.9 .times. 106 (7.0 kilobases) and pAB118B of MW 3.0 .times. 106 (4.3 kilobases). Two of the tetracycline-resistant strains each contained a plasmid (pAB124) of MW 2.9 .times. 106 (4.14 kilobases), while a third harbored a small plasmid (pAB128) of MW 2.9 .times. 106 (3.57 kilobases). These plasmids were digested with 19 different restriction endonucleases and the numbers of cleavage sites were determined. Transformation of Bacillus subtilis 168 (Trp-) with purified plasmid DNA indicated that pAB124 conferred tetracycline resistance on the host.