Alcaligenes eutrophus CH34, recently renamed Ralstonia eutrophus is a gram-negative, non-spore forming bacterium which thrives in the presence of millimolar concentrations of several heavy-metals (Zn, Cd, Co,Pb,Hg, Ni & Cr). The heavy-metal resistance is conferred by two large megaplasmids (pMOL28=180 kbp and pMOL30=240 kbp) carrying gene clusters that encode cation-efflux machinery spanning both bacterial membranes. These low-copy number plasmids are stably maintained in the presence or absence of selective pressure and are self-transferable at relatively low frequencies.
A. eutrophus uses a variety of substrates as its carbon source or it can grow chemo-lithotropically using molecular hydrogen as the energy source and carbon dioxide as a carbon source. When nitrate is present A. eutrophus can grow anaerobically.
Regions of the megaplasmid DNA relevant to the cation-efflux pump were sequenced; however, to the best of our knowledge, none of the groups is systematically sequencing any of the plasmids. The complete sequence of the megaplasmids will be instrumental in understanding gene organization, especially mechanism of plasmid replication, partition and transfer, and allowing the construction of environmentally-friendly bacteria e.g. E.coli with stable and efficient mechanism for heavy-metal resistance.
For more in depth information on biology of this bacterium, please refer to some of the following publications and references therein.
2. A. Nies et. al. "Nucleotide Sequence and Expression of a Plasmid-encoded Chromate Resistance Determinant from Alcaligenes eutrophus" J. Biol. Chem. Vol. 265 (10):5648-5653, 1990.
3. S. Taghavi et. al. "Genetic and Physical Maps of the Alcaligenes eutrophus CH34 Megaplasmid pMOL28 and its Derivative pMOL50 Obtained after Temperature-Induced Mutagenesis and Mortality" Plasmid Vol. 37:22-34, 1997.
Note: Initially we started sequencing on the libraries prepared from DNA isolated from wild type CH34 strain which has two megaplasmids. Later on we obtained cured strains with one (pMOL28) or another (pMOL30) plasmids. In addition some sequencing was done on a plasmid which has approximately 40,000 bases of chromosomal DNA incorporated into pMOL28 (called pMOL50=strain AE3).
Partial list of long-term goals includes:
Some of the genes located in CH34 megaplasmids are shown below in table 1 .
Summary information for all sequenced megaplasmids is provided in table 2.
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