The Influence of Salt Concentration on the Copy Number of Plasmid pSH1 Replicating in Micrococcus sp. 9

The study of heterotrophic bacteria isolated from the brackish waters of Lake Shira has shown that some of them contain plasmid pSH1 of approximately 2.7 kb in size. The number of plasmid copies in plasmid-containing strains cultivated at a minimal concentration of sodium chloride is found to be low, whereas the sub-culturing of these strains at high salt concentrations increases the plasmid number. The role of natural pSH1 plasmid in the osmotolerance of host bacteria is discussed.