Ralstonia metallidurans, a bacterium specifically adapted to toxic metals: towards a catalogue of metal-responsive genes

Abstract

Ralstonia metallidurans, formerly known as Alcaligenes eutrophus and thereafter as Ralstonia eutropha, is a beta-Proteobacterium colonizing industrial sediments, soils or wastes with a high content of heavy metals. The type strain CH34 carries two large plasmids (pMOL28 and pMOL30) bearing a variety of genes for metal resistance. A chronological overview describes the progress made in the knowledge of the plasmid-borne metal resistance mechanisms, the genetics of R. metallidurans CH34 and its taxonomy, and the applications of this strain in the fields of environmental remediation and microbial ecology. Recently, the sequence draft of the genome of R. metallidurans has become available. This allowed a comparison of these preliminary data with the published genome data of the plant pathogen Ralstonia solanacearum, which harbors a megaplasmid (of 2.1 Mb) carrying some metal resistance genes that are similar to those found in R. metallidurans CH34. In addition, a first inventory of metal resistance genes and operons across these two organisms could be made. This inventory, which partly relied on the use of proteomic approaches, revealed the presence of numerous loci not only on the large plasmids pMOL28 and pMOL30 but also on the chromosome. It suggests that metal-resistant Ralstonia, through evolution, are particularly well adapted to the harsh environments typically created by extreme anthropogenic situations or biotopes.

Plants as extreme environments? Ni-resistant bacteria and Ni-hyperaccumulators of serpentine flora

“…Genetic determinants for Ni resistance have been first identified and characterized at the molecular level from Alcaligenes xylosoxidans 31A (known also as Ralstonia eutropha, then as Ralstonia metallidurans and now as Cupriavidus metallidurans 31A) and Alcaligenes eutrophus CH34 (now known as Cupriavidus metallidurans CH34) which were isolated from industrially contaminated sites (Mergeay et al 1978;Schmidt and Schlegel 1989). A. xylosoxidans 31A harbors two genetic determinants (ncc, nre) on plasmid pTOM9, while C. metallidurans CH34 contains one system only (cnr) (Liesegang et al 1993;Mergeay et al 2003;Nies 2000), but a large number of transporters and a regulatory apparatus are present also in its genome constituting an integrated (both plasmid-borne and chromosomal) system for resistance to metals (Mergeay et al 2003;von Rozycki and Nies 2008). In all these systems Ni resistance is due to an inducible efflux system, mediated by ATP binding cassette (ABC) transporters, that lower the intracellular Ni concentration by pumping out Ni cations from the cytoplasm (Mergeay et al 2003).…”

“…A. xylosoxidans 31A harbors two genetic determinants (ncc, nre) on plasmid pTOM9, while C. metallidurans CH34 contains one system only (cnr) (Liesegang et al 1993;Mergeay et al 2003;Nies 2000), but a large number of transporters and a regulatory apparatus are present also in its genome constituting an integrated (both plasmid-borne and chromosomal) system for resistance to metals (Mergeay et al 2003;von Rozycki and Nies 2008). In all these systems Ni resistance is due to an inducible efflux system, mediated by ATP binding cassette (ABC) transporters, that lower the intracellular Ni concentration by pumping out Ni cations from the cytoplasm (Mergeay et al 2003). Mergeay et al (2009) presented a comprehensive review of metal resistance genes in the genus Cupriavidus.…”

Insights learned from pBTAi1, a 229-kb accessory plasmid from Bradyrhizobium sp. strain BTAi1 and prevalence of accessory plasmids in other Bradyrhizobium sp. strains

“…tomato (Mills et al, 1994). Moreover, genomic analysis has revealed a large number of similar genes on bacterial plasmids and chromosomes for a variety of other microorganisms (Mergeay et al, 1995;Francki et al, 2000;Monchy et al, 2006). The pco/copABCD operon, transcribed from a copper-inducible promoter, is controlled by the two-component regulatory module pco/copRS (Mills et al, 1994).…”

The isolation of heavy-metal resistant culturable bacteria and resistance determinants from a heavy-metal-contaminated site

“…Many studies have focused on the effects of heavy metals on bacterial community structure (Ranjard et al 2006;Ogilvie & Grant 2008;Khan et al 2010;Pechrada et al 2010), and relatively many bacteria have already been isolated from different heavy-metal-contaminated environments and their metabolic pathways for pollutant detoxification have been studied in detail. These studies included the mercury-reducing bacteria Bacillus megaterium MB1 (Huang et al 1999); the cadmium-accumulating bacteria Rhodospirillum rubrum (Smiejan et al 2003); strains resistant to multiple heavy metals (Schmidt & Schlegel 1994;Taghavi et al 1994;Mergeay et al 2003); bacteria specific to HgCl 2 -contaminated soils, such as Duganella violaceinigra, Lysobacter koreensis and Bacillus panaciterrae (Mera & Iwasaki 2007); cadmium-resistant bacteria, such as Alcaligenes xylosoxidans, Comamonas testosteroni, Klebsiella planticola, Pseudomonas fluorescens and Serratia liquefaciens (Chovanová et al 2004); Ochrobactrum sp. (Pandey et al 2010); a Ralstonia pickettii strain, highly Isolation of culturable bacteria and resistance determinants 19 resistant to cadmium, and a Sphingomonas sp.…”