Geobacter metallireducens is a gram negative rod bacteria, sometimes with a flagella. It belongs to the Phylum Proteobacteria, Class Deltaproteobacteria, Order Desulfuromonadales, Family Geobacteraceae (1, 2). It is an anaerobe, using Iron (III) Oxide as an electron acceptor. Metallireducens prefers 30oC, in aquatic environments, in the presence of iron (III) oxide. It is a chemolithohertroph, meaning it utilizes reduced inorganic molecules, does not use light as an energy source, and uses reduced organic molecules as a carbon source. It it not known to be pathogenic in any organism. This bacteria prefers a slightly acidic environment (pH 6.8) with 0% salt concentration (6).
The unique metabolism of metallireducens enables it to actually feed off of rust. It turns iron (III) oxide into nano sized pieces of iron (7). This can easily be detected using a magnet, as iron is magnetic and iron (III) oxide is not (4).
Figure1: The Iron Cycle. Metallireducens converts Fe3+ to Fe2+
Metallireducen was first discovered near Potomac River, Washington DC, in 1987 (3). While the geographical distribution of G. metallireducen is not known, but it would seem that it could be found in water and soils worldwide.
A synopsis of: "Hexahydro-1,3,5-trinitro-1,3,5-triazine Transformation by Biologically Reduced Ferrihydrite: Evolution of Fe Mineralogy, Surface Area, and Reaction Rates" (5)
Background: The respiration of Geobacter metallireducens converts Iron (III) oxide to magnetic Iron, while reducing the concentration of a contaminant Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX).
Objective: The objective of this study was to find out how the evolution of the Fe phases over time can affect the ability to reduce contaminants.
Methods: RDX was added to a culture G. metallireducens in the presence of ferrihydrite, and over a range of 7 to 400 days, the amount of reduction intermediates from RDX were measured.
Main findings: This article suggests that continuous reduction of Iron (III) Oxide may be essential to remediation, and that G. metallireducens proves one avenue for contaminant reduction.
Significance: In an first world country, pollution and contamination is becoming a larger problem. Looking to microbes for bioremediation may prove to be the most effective cleanup methods yet.
Interesting Facts:
Figure2: Expressed flagella and pili
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Metallireducens have genes that code for a flagella. When the bacteria is near insoluble food sources, it can "sniff" them out, grow a flagella, and move to where it needs to go (3).
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One strain of Geobacter, Strain 121, loves temperatures at 121oC. It survives up to 130oC. Don't believe me? Lazy? Click to listen.
Figure3: Filaments coming out of a G. metallireducens
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Worlds smallest wires? Maybe. These filaments growing out of the bacteria are like small wires, transferring electrons from out of the cell to insoluable electron acceptors.
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Metallireducens may clean plutonium, uranium, and petroleum contaminants.
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It may be possible to make microbial fuel cells, converting waste organic matter to electricity.
Figure4: Jim was quite surprised to see a rod bacteria using the Iron Cycle
Words:
(1) Prescott, Lansing M., John P.Harley, and Donald A. Klein. 2005. Microbiology, 6th edition. McGraw-Hill, Toronto.
(2) Sneath, Peter H., editor. Bergey’s manual of Systematic Bacteriology, Volume 2. 1986. Lippincott, Williams & Wilkins, New York.
(3) http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=genomeprj&cmd=Retrieve&dopt=Overview&list_uids=177
(4) Childers, Susan E. 2002. Geobacter metallireducens accesses insoluble Fe(III) oxide by chemotaxis. Nature Volume 416 Issue 6882. Pp 767-769
(5) Gregory, Kelvin B.; Parkin, Gene F.; Scherer, Michelle M.; and Williams, Aaron G.B.. 2004. Hexahydro-1,3,5-trinitro-1,3,5-triazine Transformation by Biologically Reduced Ferrihydrite: Evolution of Fe Mineralogy, Surface Area, and Reaction Rates. Environmental Science Technology Volume 39. Pp 5183-89.
(6) http://pmb.berkeley.edu/~coates/culturecollection/Geobacter%20metallireducens%20GS15.htm
(7) http://www.uga.edu/srel/Reprint/2796.htm
(8) http://genome.jgi-psf.org/draft_microbes/geome/geome.home.html
Pictures
Title Pictures: http://www.geobacter.org/images/Geobacter-Fe(III)-sm.jpg
Figure 1: Prescott, Lansing M., John P.Harley, and Donald A. Klein. 2005. Microbiology, 6th edition. McGraw-Hill, Toronto.
Figure 2: http://www.genomenewsnetwork.org/gnn_images/news_content/04_02/geobacter/geobacter1.jpg
Figure 3: http://www.geobacter.org/research/nanowires/images/jpg/Complement-main.jpg
Figure 4: http://www.willarton.com/toy/BIIBM.gif
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