Horizontal Gene Transfer in Metal and Radionuclide Contaminated Soils

Abstract

The horizontal transfer of genes encoded on mobile genetic elements (MGEs) such as plasmids and phage and their associated hitchhiking elements (transposons, integrons, integrative and conjugative elements, and insertion sequences) rapidly accelerate genome diversification of microorganisms, thereby affecting their physiology, metabolism, pathogenicity,and ecological character. The analyses of completed prokaryotic genomes reveal that horizontal gene transfer (HGT) continues to be an important factor contributing to the innovation of microbial genomes. Indeed, microbial genomes are remarkably dynamic and a considerable amount of genetic information is inserted or deleted by HGT mechanisms. Thus, HGT and the vast pool of MGEs provide microbial communities with an unparalleled means by which to respond rapidly to changing environmental conditions and exploit new ecological niches. Metals and radionuclide contamination in soils, the subsurface, and aquifers poses a serious challenge to microbial growth and survival because these contaminants cannot be transformed or biodegraded into non-toxic forms as often occurs with organic xenobiotic contaminants. In this chapter we present cases in which HGT has been demonstrated to contribute to the dissemination of genes that provide adaptation to contaminant stress (i.e., toxic heavy metals and radionuclides). In addition, we present directions for future studies that could provide even greater insights into the contributions of HGT to adaptation for survival in mixed waste sites.

Insights into the resistance and resilience of the soil microbial community

“…The transfer of mobile genetic element by plasmids among taxonomically diverse bacteria in soil is well described (Springael & Top, 2004) and can contribute to the dissemination of genes that provide resistance to contaminant stress (reviewed in Smalla & Sobecky, 2002;Sobecky & Coombs, 2009). The transfer of mobile genetic element by plasmids among taxonomically diverse bacteria in soil is well described (Springael & Top, 2004) and can contribute to the dissemination of genes that provide resistance to contaminant stress (reviewed in Smalla & Sobecky, 2002;Sobecky & Coombs, 2009).…”

Horizontal Gene Exchange in Environmental Microbiota

“…In freshwater microcosms, amendment with metal concentrations representative of industry and mining-impacted environments increased the frequency of antibiotic resistance in the microbial communities (Stepanauskas et al, 2006). Genetic mechanisms responsible for the co-selection phenomena in the contaminated environments are presently poorly understood, but it is clear that the MGE-driven HGT is the main adaptive trait in bacteria inhabiting industrially contaminated aquatic (Wright et al, 2008) and soil (Top et al, 1995; Sobecky and Coombs, 2009) ecosystems.…”

Aerobic biodegradation of the chloroethenes: pathways, enzymes, ecology, and evolution

“…Horizontal gene transfer (HGT) processes, especially conjugation, are powerful contributors to the evolution of xenobiotic degradation pathways (Top & Springael, 2003;van der Meer & Sentchilo, 2003). Our recognition of the importance of HGT in microbial evolution began with the discovery of the spread of antibiotic resistance genes (Cohen, 1992), but it is now clear that many accessory functions in bacteria are encoded on plasmids or other MGEs, including metal resistance (Sobecky & Coombs, 2009), virulence factors (Hogenhout & Loria, 2008;Kolstø et al, 2009), plant symbiosis (MacLean et al, 2007, secondary metabolite biosynthesis (Kinashi et al, 1992), and xenobiotic catabolism (Top & Springael, 2003;Nojiri et al, 2004).…”