Geobacter metallireducens

{{Short description|Species of bacterium}}

{{Speciesbox

| taxon = Geobacter metallireducens

| authority = Lovley et al. 1995

}}

Geobacter metallireducens is a gram-negative metal-reducing proteobacterium.{{cite journal | vauthors = Lovley DR, Giovannoni SJ, White DC, Champine JE, Phillips EJ, Gorby YA, Goodwin S | title = Geobacter metallireducens gen. nov. sp. nov., a microorganism capable of coupling the complete oxidation of organic compounds to the reduction of iron and other metals | journal = Archives of Microbiology | volume = 159 | issue = 4 | pages = 336–344 | year = 1993 | pmid = 8387263 | doi = 10.1007/BF00290916 | bibcode = 1993ArMic.159..336L | s2cid = 21365293 }} It is a strict anaerobe that oxidizes several short-chain fatty acids, alcohols, and monoaromatic compounds with Fe(III) as the sole electron acceptor.{{cite journal | vauthors = Tremblay PL, Aklujkar M, Leang C, Nevin KP, Lovley D | title = A genetic system for Geobacter metallireducens: role of the flagellin and pilin in the reduction of Fe(III) oxide | journal = Environmental Microbiology Reports | volume = 4 | issue = 1 | pages = 82–88 | date = February 2012 | pmid = 23757233 | doi = 10.1111/j.1758-2229.2011.00305.x | bibcode = 2012EnvMR...4...82T | s2cid = 28743447 }} It can also use uranium for its growth and convert U(VI) to U(IV).{{cite journal | vauthors = Koribanics NM, Tuorto SJ, Lopez-Chiaffarelli N, McGuinness LR, Häggblom MM, Williams KH, Long PE, Kerkhof LJ | title = Spatial distribution of an uranium-respiring betaproteobacterium at the Rifle, CO field research site | journal = PLOS ONE | volume = 10 | issue = 4 | pages = e0123378 | year = 2015 | pmid = 25874721 | pmc = 4395306 | doi = 10.1371/journal.pone.0123378 | bibcode = 2015PLoSO..1023378K | doi-access = free }}

Geobacter metallireducens was discovered by Derek Lovley at UMass Amherst in 1993. It is an iron-reducing bacteria and it has been thought that the microbe could be used to treat industrial sites where "cyanide-metal complexes" have formed to contaminate the site.{{cite journal | vauthors = Childers SE, Ciufo S, Lovley DR | title = Geobacter metallireducens accesses insoluble Fe(III) oxide by chemotaxis | journal = Nature | volume = 416 | issue = 6882 | pages = 767–769 | date = April 2002 | pmid = 11961561 | doi = 10.1038/416767a | bibcode = 2002Natur.416..767C | s2cid = 2967856 }}

The genome of Geobacter metallireducens has a chromosome length of 3,997,420 bp. It has a circular bacterial chromosome, meaning there are no free ends of DNA. The shape is roughly like that of an egg.{{cite journal |vauthors=Aklujkar M, Krushkal J, DiBartolo G, Lapidus A, Land ML, Lovley DR |date=May 2009 |title=The genome sequence of Geobacter metallireducens: features of metabolism, physiology and regulation common and dissimilar to Geobacter sulfurreducens |journal=BMC Microbiology |volume=9 |pages=109 |doi=10.1186/1471-2180-9-109 |pmc=2700814 |pmid=19473543 |doi-access=free}} Geobacter metallireducens also has a GC content of 59.51%. The plasmid has a lower GC content, of 52.48%, and is 13,762 bp in length. The plasmid encodes a stabilizing protein, RelE/ParE, which allows Geobacter metallireducens to adapt and thrive in different and new environmental conditions.{{cite journal |vauthors=Anantharaman V, Aravind L |date=2003 |title=New connections in the prokaryotic toxin-antitoxin network: relationship with the eukaryotic nonsense-mediated RNA decay system |journal=Genome Biology |volume=4 |issue=12 |pages=R81 |doi=10.1186/gb-2003-4-12-r81 |pmc=329420 |pmid=14659018 |doi-access=free}}

Geobacter metallireducens becomes motile when necessary, producing a flagellum in order to relocate when environmental conditions become unfavorable. Insoluble Fe(II) and Mn (II) are electron acceptors for many chemolithotrophic microorganisms. Fe (II) is produced through the reduction of Fe(III) and Mn (IV) oxides. It is often difficult for these organisms to attain iron and manganese because Fe(III) and Mn (IV) oxides do not freely diffuse through bacterial membranes. Geobacter metallireducens has evolved a unique way to access iron via insoluble Fe(III) and Mn (IV) oxides; they grow motility appendages to help them find and contact the insoluble oxides. {{Cite journal |last1=Childers |first1=Susan E. |last2=Ciufo |first2=Stacy |last3=Lovley |first3=Derek R. |date=April 2002 |title=Geobacter metallireducens accesses insoluble Fe(iii) oxide by chemotaxis |url=https://www.nature.com/articles/416767a |journal=Nature |language=en |volume=416 |issue=6882 |pages=767–769 |doi=10.1038/416767a |bibcode=2002Natur.416..767C |issn=1476-4687}} According to a study conducted by Childers et. al., cells of G. metallireducens that grew in an environment with insoluble Fe(III) and Mn (IV) oxides grew flagella and pili. Whereas those grown in environments with soluble Fe(III) and Mn (IV) oxides did not have flagella nor pili. G. metallireducens is only motile when there are no soluble Fe(III) and Mn (IV) oxides in its environment to act as the electron acceptor. It is the first known microorganism to display chemotactic tendencies towards iron and manganese, as well as the first microbe discovered that oxidizes organic compounds with the inorganic elements iron and manganese.

G. metallireducens does not solely reduce Fe(III) and Mn(IV) oxides, it can reduce a variety of compounds including those that are toxic or radioactive such as uranium, plutonium, technetium, and vanadium.{{Cite journal |last1=Sun |first1=Jun |last2=Sayyar |first2=Bahareh |last3=Butler |first3=Jessica E |last4=Pharkya |first4=Priti |last5=Fahland |first5=Tom R |last6=Famili |first6=Iman |last7=Schilling |first7=Christophe H |last8=Lovley |first8=Derek R |last9=Mahadevan |first9=Radhakrishnan |date=December 2009 |title=Genome-scale constraint-based modeling of Geobacter metallireducens |journal=BMC Systems Biology |language=en |volume=3 |issue=1 |doi=10.1186/1752-0509-3-15 |doi-access=free |issn=1752-0509 |pmc=2640342 |pmid=19175927}} Vanadium, specifically, can contaminate groundwater in areas near high mining activity. G. metallireducens can utilize vanadium (V) as an energy source by reducing the metal to vanadium (IV). Therefore the bacteria can be used to aid in decontamination of affected groundwaters.

In 2002, a pilot field test was conducted to examine the efficacy of using G. metallireducens to decontaminate a former vanadium and uranium ore processing site in Rifle, Colorado. Due to the leaching of tailing piles, vanadium(V) groundwater concentrations up to 50 μM were found near the site. Acetate was used as an electron donor and pumped into the groundwater aquifer for 50 days. Test wells downgradient of the injection site showed a decline in vanadium(V) levels within 9 days and either undetectable levels or levels below the human health risk-based concentration (6 μM) within 39 days. Wells upgradient of the acetate injection did not see a significant change. In this same time period, a significant increase in the proportion of bacteria from the Geobacteraceae family was observed, lending strong evidence for the biotic precipitation of vanadium(V) out of the groundwater by G. metallireducens.{{Cite journal |last=Ortiz-Bernad |first=Irene |last2=Anderson |first2=Robert T. |last3=Vrionis |first3=Helen A. |last4=Lovley |first4=Derek R. |date=May 2004 |title=Vanadium Respiration by Geobacter metallireducens: Novel Strategy for In Situ Removal of Vanadium from Groundwater |url=https://journals.asm.org/doi/full/10.1128/aem.70.5.3091-3095.2004 |journal=Applied and Environmental Microbiology |volume=70 |issue=5 |pages=3091–3095 |doi=10.1128/AEM.70.5.3091-3095.2004 |pmc=404428 |pmid=15128571}}

G. metallireducens can use a similar mechanism to reduce uranium (VI) to uranium (V) in contaminated groundwaters. However, there is still research to be done on making this process more effective. {{Cite journal |last1=Anderson |first1=Robert T. |last2=Vrionis |first2=Helen A. |last3=Ortiz-Bernad |first3=Irene |last4=Resch |first4=Charles T. |last5=Long |first5=Philip E. |last6=Dayvault |first6=Richard |last7=Karp |first7=Ken |last8=Marutzky |first8=Sam |last9=Metzler |first9=Donald R. |last10=Peacock |first10=Aaron |last11=White |first11=David C. |last12=Lowe |first12=Mary |last13=Lovley |first13=Derek R. |date=October 2003 |title=Stimulating the In Situ Activity of Geobacter Species To Remove Uranium from the Groundwater of a Uranium-Contaminated Aquifer |journal=Applied and Environmental Microbiology |language=en |volume=69 |issue=10 |pages=5884–5891 |doi=10.1128/AEM.69.10.5884-5891.2003 |pmc=201226 |bibcode=2003ApEnM..69.5884A |issn=0099-2240}}

G. metallireducens has been demonstrated to reduce chloramphenicol (CAP) to complete dechlorination products under pure culture conditions. Research utilizing cyclic voltammograms and chronoamperometry revealed that the bacteria exhibited a negative correlation CAP removal efficiency with initial CAP dosages, displaying the organism's potential application of bioremediation in environments polluted by antibiotics.Xu, H., Xiao, L., Zheng, S. et al. "Reductive degradation of chloramphenicol by Geobacter metallireducens". Sci. China Technol. Sci. 62, 1688–1694 (2019). {{doi|10.1007/s11431-018-9415-2}}

G. metallireducens can make electrical connections with other microbes. This, in turn, allows other microbes to perform anaerobic syntrophic metabolism of organic substrates. This process of this electrical connection is called direct interspecies electron transfer (DIET). DIET is a metabolism that is defined by the movement of free electrons, rather than organisms only receiving electrons via the reduction of other compounds. {{Citation |last1=Dubé |first1=Charles-David |title=Direct Interspecies Electron Transfer in Anaerobic Digestion: A Review |date=2015 |work=Biogas Science and Technology |volume=151 |pages=101–115 |editor-last=Guebitz |editor-first=Georg M. |url=https://link.springer.com/10.1007/978-3-319-21993-6_4 |access-date=2024-04-12 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-21993-6_4 |isbn=978-3-319-21992-9 |last2=Guiot |first2=Serge R. |pmid=26337845 |editor2-last=Bauer |editor2-first=Alexander |editor3-last=Bochmann |editor3-first=Guenther |editor4-last=Gronauer |editor4-first=Andreas}} The pili of G. metallireducens conduct electrical currents. They can transfer electrons to other Geobacter species as well as archaea, specifically methanogens. The DIET connection to methanogens allows these bacteria to contribute to the methane cycle, and convert organic wastes to methane. {{Cite journal |last=Lovley |first=Derek R. |date=2022-02-16 |title=Microbe Profile: Geobacter metallireducens: a model for novel physiologies of biogeochemical and technological significance: This article is part of the Microbe Profiles collection. |journal=Microbiology |language=en |volume=168 |issue=2 |doi=10.1099/mic.0.001138 |doi-access=free |issn=1350-0872}}