An examination of the plasmids and megacin of Bacillus megaterium QM B1551
Weickert, Michael J.
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Bacillus megaterium strains have been reported to produce bacteriocins known as megacins. Relatively large amounts of plasmid DNA have also been found. Since strain QM B1551 is currently of interest because its genome is being mapped by transduction, it was also tested for megacin production and the presence of plasmids. A megacin was found that was not UV inducible and was produced only on solid media by young cells. It was not comparable to megacin A, the best-characterized megacin, but was similar to megacin C. When tested for plasmids, strain QM B1551 had at least 11% of its total cellular* DNA recoverable in the form of covalently closed circular or plasmid DNA. This DNA contained several discrete size classes as determined by sucrose ultracentrifugation, agarose gel electrophoresis, and electron microscopy. The plasmid sizes were: 3.5, 5.3, 12, 31, 43, 70, and 109 million daltons (md). They were present in estimated copy numbers ranging from 1 for the 109 md plasmid to 135 for the smallest. This collection of plasmids was compared to that of other B. megaterium strains by simultaneous agarose gel electrophoresis and was found to be unique. The first determination of plasmids for strain KM, a megacin-sensitive strain, was also made.