Characterization of plasmids in Erwinia stewartii

Plasmids in 39 strains of Erwinia stewartii were examined by agarose gel electrophoresis. Most virulent strains had from 11 to 13 plasmids ranging in molecular mass from 2.8 to 210 megadaltons and contained plasmids of 210, 70, 49, 43, 29.5, 16.8, 8.8, and 2.8 megadaltons. Plasmids in strains SW2 and SS104 were characterized by both electron microscopy and agarose gel electrophoresis and may be useful as convenient references for sizing plasmids by electrophoresis. Specific size classes of plasmids could not be associated with antibiotic and heavy metal resistance, carbohydrate utilization, bacteriocin production, or pathogenicity to corn. However, avirulent strains tended to have fewer plasmids than virulent strains.