Ralstonia metallidurans

A Microbial Biorealm page on the genus Ralstonia metallidurans

Bacterial induced formation of Cd crystals by Ralstonia metallidurans on Zirfon M5 membranes in the continuous tubular membrane reactor.. [1]

Classification

Higher order taxa

Kingdom: Bacteria Phylum: Proteobacteria Class: Beta Proteobacteria Order:Burkholderiales Family: Ralstoniaceae Genus: Ralstonia Species: R. metallidurans Strain: CH3

Species

NCBI: Taxonomy

Ralstonia solanacearum

Ralstonia oxalatica

Ralstonia paucula

Ralstonia pickettii

Genus species

Description and significance

Alcaligenes eutrophus CH34, was just recently renamed Ralstonia metallidurans
. It was first isolated in 1976 from the sludge of a zinc decantation tank in Belgium that was polluted with high concentrations of several heavy metals, it and other metal-resistant members of the genus Ralstonia are frequently found in sediments and soils with a high content of heavy metals from diverse geographical locations.

Ralstonia metallidurans is gram-negative, non-spore forming bacterium which thrives in the presence of millimolar concentrations of several heavy-metals; Zn, Cd, Co,Pb,Hg, Ni and Cr. Metal resistance functions are mainly encoded on two plasmids, pMOL28 and pMOL30, which produce metal exporters that pump metal ions out of the cell, protecting intracellular macromolecules from the toxic effects of high concentrations of metal.

This extremophile is better able to withstand high concentrations of heavy metals than any other well-studied organism. This fact renders it a potential agent of bioremediation as well as an ideal model organism for understanding metal resistance phenotypes. Due to its survival in extreme metal concentrations and genomic sequencing it is thought to be one of the first life forms on earth, existing when there was very little oxygen in the atmosphere some 2.5 billion years ago.

Genome structure

Its genome is approximately 6800 kb in size. The type strain CH34 carries two large circular plasmids(pMOL28=180 kbp and pMOL30=240 kbp)and two circular chromosomes bearing a variety of genes for metal resistance and carrying gene clusters that encode cation-efflux machinery spanning both bacterial membranes. These low-copy number plasmids are maintained in the presence or absence of selective pressure and are self-transferable at relatively low frequencies.

. Circular genomes for Ralsontia metallidurans found using tools.neb.com

The genome of this bacterium contains also 8 P-type ATPase involved in metal efflux specialized in lead, cadmium, thallium and/or copper efflux, and several others mechanisms involved in metal processing.

Cell structure and metabolism

Ralstonia metallidurans uses a variety of substrates as its carbon source. It can grow chemo-lithotropically using molecular hydrogen as the energy source and carbon dioxide as a carbon source to form a cytoplasmic NAD-reducing and a membrane-bound hydrogenase. It contains most metabolic attributes; however, it does not grow on fructose(5).R. metallidurans
can reduce selenite to elemental red selenium, metabolize glutamatee, ascorbate, aldarate and nitrogen. When nitrate is present Ralsonia metallidurans can grow anaerobically. Its optimal growth temperature is 30 çC.

Ralstonia metallidurans
is rod-shaped, motile aerobe. It is a gram-negative bacteria and pocesses such traits as the cell walls contain peptidoglycan; Cells are surrounded by an outer membrane containing lipopolysaccharide; Porins exist in the outer membrane, which act like pores for particular molecules; There is a space between the layers of peptidoglycan and the secondary cell membrane called the periplasmic space; The S-layer is directly attached to the outer membrane, rather than the peptidoglycan; No teichoic acids or lipoteichoic acids are present.

Ecology

Due to its ability to withstand high concentrations of heavy metals it renders it as a potential agent of bioremediation of soil and water contaminated with heavy metals or chlorinated organic compounds as well as an ideal model organism for understanding metal resistance phenotypes.

Lead contamination is a serious threat to human health and the environment. Lead levels are typically measured by using atomic absorption spectroscopy or other related instrumental methods. Developent of fluorescent Lead II Probe from Lead II-regulatory protein isolated from Ralstonia Metallidurans could provide rapid, on-site evaluation of the lead content of a sample.

Pathology

Ralstonia metallidurans is not a pathogen and does not inhabit any host organisms. However, many other species of Ralsontonia can be pathogenic to plants (Ralstonia solanacearum)
and have been seen in cystic fibrosis patients(Ralstonia pickettii
). Many species of gram-negative bacteria such as R. metallidurans
are pathogenic. This pathogenic capability is usually associated with certain components of gram-negative cell walls, in particular the lipopolysaccharide (also known as LPS or endotoxin) layer. The LPS is the trigger which the body's innate immune response receptors sense to begin a cytokine reaction which is toxic to the host.

Application to Biotechnology

Interestingly, enzymes from Ralstonia metallidurans were used by scientists in constructing a fuel cell(2). By encasing a pair of electrodes coated with these enzymes from Ralstonia metallidurans which oxidize hydrogen put inside a container filled with air and 3 percent more hydrogen (2). Trials of the fuel cell produced enough electricity to make a watch work. Larger scale productions are thought to be possible and are in the making.

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Colored scanning electron image of bacterioform gold on a gold grain from the Hit or Miss Mine in northern Queensland. [2]

Current Research

It is being researched that Ralstonia metallidurans could be involved in precipitating gold out of solution. It has an ability to survive in gold concentrations that would kill most other organisms(1)."It is possible that the microbe screens out the gold as part of an effort to detoxify its immediate environment"(1).

References

1.Llyod, Robin. "Eureka! Bacteria Have the Midas Touch" 18 July 2006.<http://www.livescience.com/othernews/060718_gold_bacteria.html>

2.American Chemical Society."New 'biofuel cell' produces electricity from hydrogen in plain air."26 March 2007. <http://www.physorg.com/news94144517.html>

3. 5. http://jb.asm.org/cgi/content/abstract/162/1/328 Edited by student of Rachel Larsen and Kit Pogliano