Mercury-resistant plasmids in bacteria from a mercury and antimony deposit area

Most bacterial cells (Pseudomonas, Acinetobacter) obtained from the soil at the Khaidarkan mercury and antimony mine (Kirghiz USSR) contain R plasmids with mercury (HgCl2) resistance determinants. The plasmids have a large molecular mass (about 100 MD, though smaller ones also occur), and at least some of them are transmissive. Many of the Hgr bacteria also display an elevated antimony (SbCl3) resistance, though this trait was not shown to be plasmid-dependent. There are practically no Hgr plasmids in bacteria taken from the soil at different distances from the mine: the saturation of bacteria with Hgr plasmids is maintained by selective pressure only in the area with a high enough toxin concentration. In the same mercury and antimony deposit area Hgr plasmids were also found in Escherichia coli isolates from the gut of Mus musculus mice and Bufo viridis toads. At least some of the bacterial plasmids obtained from animals also carry antibiotic-resistance determinants (Tcr, Cmr, Smr). These plasmids are also transmissive. They display internal instability and lose their resistance determinants after a conjugation transfer to other E. coli strains.