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

Abstract

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-1␤ replicon-specific sequences detected in total community DNA. The isolation of IncP-1␤ 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-1␤ plasmids in the genomic DNA of the cultured Hg-resistant bacterial isolates. However, without selection for mercury resistance, three different IncP-1␤ 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 merRT⌬P 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-1␤ plasmids R751 and pB8. However, this is the first example of an IncP-1␤ 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.

Quaternary ammonium compounds in soil: implications for antibiotic resistance development

“…These plasmids and transposons include multiresistance and heavy metal resistance plasmids as, for example reported for qacA and qacB genes, respectively (Russell 1997), but they were also associated with degradative pathways in a pesticide polluted environment (Dealtry et al 2014). Class 1 integrons including qac genes are frequently found on IncP-1 plasmids which are broad host range plasmids widely distributed in the environment such as soil, manure, sludge, digestates and river sediments (Jechalke et al 2015;Smalla et al 2006;Zhang et al 2011b;Heuer et al 2012;Popowska and Krawczyk-Balska 2013;Wolters et al 2015). For example, IncP-1e plasmids were detected by qPCR in 16 manure samples and in arable soil (Heuer et al 2012).…”

Spatial structure and nutrients promote invasion of IncP-1 plasmids in bacterial populations

“…Plasmids of the incompatibility group P-1 (IncP-1 plasmids) transfer very efficiently to a wide range of hosts and are abundant in several environments (Thomas and Smith, 1987;Top et al, 2000;Smalla et al, 2006, Schlü ter et al, 2007. They are known to transfer at much higher rates on solid substrates than in mixed liquids.…”

Influence of industrial contamination on mobile genetic elements: class 1 integron abundance and gene cassette structure in aquatic bacterial communities

“…Several studies have detected MGEs including plasmids, transposons and integrons across a wide variety of habitats (for example, Sobecky, 1999;Smalla and Sobecky, 2002;van Elsas and Bailey, 2002;Frost et al, 2005), but rarely in a quantitative manner due to previous methodological constraints. In those studies that did quantify MGE abundance in bacterial communities, class 1 integrase (intI1) genes were shown to be abundant in Gram-positive and Gram-negative bacteria in poultry litter obtained from farms with varying antibiotic usage regimes regardless of antibiotic usage (Nandi et al, 2004), while mercury exposure was recently demonstrated to increase the abundance of IncP-1 plasmids (Smalla et al, 2006). Yet, how MGE abundance is affected by environmental conditions and selective pressures is poorly understood and remains to be tested systematically.…”