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

Abstract

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.

Occurrence, Transfer and Mobilization in Epilithic Strains of Acinetobacter of Mercury-resistance Plasmids Capable of Transformation

“…The plasmid pQM17 had a broad host range when mobilized by RP1 (Table 1) as did pKLl (Lomovskaya et af., 1986). This suggests that small non-conjugative plasmids as well as conjugative plasmids (Kelly & Reanney, 1984;Khesin & Karasyova, 1984;Rochelle et al, 1989) might be important in the maintenance and spread of mercury resistance genes in natural bacterial populations. However, pQM17 was probably not abundant in epilithic bacteria because further attempts to isolate plasmids that were able to transform BD413 to mercury resistance were unsuccessful.…”

“…Most research on transferable resistances in bacteria isolated from natural environments has concentrated on conjugative plasmids (Kelly & Reanney, 1984;Khesin & Karasyova, 1984;Toranzo et al, 1984;Gauthier et al, 1985), but it has been suggested that the most common types of plasmid in bacteria are small (<20 kb) and therefore non-conjugative (Kelly & Reanney, 1984).…”

“…are common in soil and water (Bauman, 1968 ;Juni, 1972;Khesin & Karasyova, 1984). It is therefore possible that Acinetobacter spp.…”

Intercontinental spread of promiscuous mercury‐resistance transposons in environmental bacteria

“…These genes are organized into well-characterized mer operons that are usually located on plasmids and transposons (Silver and Waldeerhaug, 1992;Grinsted et al, 1990). Bacteria carrying mer operons are ubiquitous, being present in great numbers in areas with increased mercury concentrations such as mercury mines (Khesin and Karasyova, 1984) or contaminated soils and waters . They are also invariably found in small numbers in pristine environments.…”

Tn5041-like transposons: molecular diversity, evolutionary relationships and distribution of distinct variants in environmental bacteria b bThe accession numbers for the nucleotide sequences reported in this work are given in the legends for Figs 1 F1 and 2. c cA comparison of the sequence of INT5041C with other proteins is available as supplementary data on Microbiology Online (http://mic.sgmjournals.org).

“…The environmental Hg R strains screened in this study were from the IMG-Hg Reference Collection partly described previously (Khesin & Karasyova, 1984 ;Bogdanova et al, 1988 ;Yurieva et al, 1997 ;Mindlin et al, 2001). The strains characterized in this study are listed in Table 1 ; their identification was performed as described (Khesin & Karasyova, 1984 ;Bogdanova et al, 1988).…”