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Applied and Environmental Microbiology, November 2006, p. 7253-7259, Vol. 72, No. 11
0099-2240/06/$08.00+0     doi:10.1128/AEM.00922-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Increased Abundance of IncP-1ß Plasmids and Mercury Resistance Genes in Mercury-Polluted River Sediments: First Discovery of IncP-1ß Plasmids with a Complex mer Transposon as the Sole Accessory Element

Federal Biological Research Centre for Agriculture and Forestry (BBA), Messeweg 11-12, 38104 Braunschweig, Germany,¹ School of Biological Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom,² GSF National Research Center for Environment and Health—Institute for Soil Ecology, Ingolstädter Landstr. 1, 85758 Oberschleissheim, Germany³

Received 19 April 2006/ Accepted 11 September 2006

Although it is generally assumed that mobile genetic elements facilitate the adaptation of microbial communities to environmental stresses, environmental data supporting this assumption are rare. In this study, river sediment samples taken from two mercury-polluted (A and B) and two nonpolluted or less-polluted (C and D) areas of the river Nura (Kazakhstan) were analyzed by PCR for the presence and abundance of mercury resistance genes and of broad-host-range plasmids. PCR-based detection revealed that mercury pollution corresponded to an increased abundance of mercury resistance genes and of IncP-1ß replicon-specific sequences detected in total community DNA. The isolation of IncP-1ß plasmids from contaminated sediments was attempted in order to determine whether they carry mercury resistance genes and thus contribute to an adaptation of bacterial populations to Hg pollution. We failed to detect IncP-1ß plasmids in the genomic DNA of the cultured Hg-resistant bacterial isolates. However, without selection for mercury resistance, three different IncP-1ß plasmids (pTP6, pTP7, and pTP8) were captured directly from contaminated sediment slurry in Cupriavidus necator JMP228 based on their ability to mobilize the IncQ plasmid pIE723. These plasmids hybridized with the merRTP probe and conferred Hg resistance to their host. A broad host range and high stability under conditions of nonselective growth were observed for pTP6 and pTP7. The full sequence of plasmid pTP6 was determined and revealed a backbone almost identical to that of the IncP-1ß plasmids R751 and pB8. However, this is the first example of an IncP-1ß plasmid which had acquired only a mercury resistance transposon but no antibiotic resistance or biodegradation genes. This transposon carries a rather complex set of mer genes and is inserted between Tra1 and Tra2.

Published ahead of print on 15 September 2006.

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