Physical Characterization of Extra-Chromosomal DNA in Chesapeake Bay Bacteria from Polluted and Non Polluted Sites

摘要

The significance of extrachromosomal elements in natural populations of estuarine bacteria has not been determined. To obtain measure of the frequency of plasmids in this ecosystem, a random sample of the total aerobic heterotrophic community was collected from the Chesapeake Bay. Two hundred eighteen strains were examined by agarose gel electrophoresis, using an in-the-well lysis procedure. Forty four percent of these isolates carried at least one plasmid. This proportion did not vary significantly between three different sampling locations which span an enormous range of water quality. In general, organisms isolated from cleaner stations contained predominantly single, small plasmids with a molecular weight of three to five megadaltons. A significantly large percentage of bacteria isolated from Baltimore's inner harbor tended to carry multiple plasmids and plasmids greater than 30 times 10 to the 6th power molecular weight. Plasmids were identified in organisms representing all the major taxonomic components of the estuarine aerobic heterotrophic community. Plasmids of the three to five megadalton size class were found to be extremely ubiquitous. DNA-DNA hybridization analysis between plasmid DNA from several isolates indicate that within a group of heterogeneous small cryptic plasmids may exist several groups of structurally related plasmids of both narrow and broad host range. Future work will be needed to further determine the extent of these homologies.