Geopsychrobacter electrodiphilus

Geopsychrobacter electrodiphilus is a species of bacteria, the type species of its genus.[lower-alpha 1] It is a psychrotolerant member of its family, capable of attaching to the anodes of sediment fuel cells and harvesting electricity by oxidation of organic compounds to carbon dioxide and transferring the electrons to the anode.[1]

Geopsychrobacter electrodiphilus
Scientific classification
Kingdom:
Bacteria
Phylum:
Proteobacteria
Class:
Deltaproteobacteria
Order:
Desulfuromonadales
Family:
Geobacteraceae
Genus:
Geopsychrobacter
Species:
G. electrodiphilus
Binomial name
Geopsychrobacter electrodiphilus
Holmes et al. 2005

In microbial communities, G. electrodiphilus could be similar to other Geobacteraceae.[1] The community may ferment complex organic matter, thereby breaking up plant matter, for example; G. electrodiphilus would then oxidize the fermentation products (especially acetate) to carbon dioxide, whereby a terminal electron acceptor [e.g. iron(III) oxide] would be reduced.[1] At least one strain (A1T) can oxidize hydrogen too.[1]

Since G. electrodiphilus belongs to the Geobateraceae and can transfer electrons to the outside,[1] one could assume that electron transfer to a methane producing archaeon could happen. There is another member of Geobacteraceae, well invetigated for its interspecies electron transfer, even to a methanogen.[2]

Description

Geopsychrobacter electrodiphilus was isolated from the surface of an electrode (anode) of a marine sediment fuel cell. The sediments come from a water depth of 5 meters (Boston Harbor, Massachusetts, near the peninsula World's End).[1]

The name "Geopsychrobacter electrodiphilus" means somewhat like "electrode-loving rod of cold earth" and indicates that the microbe comes from the surface (earth, Geo), copes with cold (psychro), is rod-shaped (bacter) and was isolated from electrodes (electrodi), which it has voluntarily settled (philus).[1]

Two strains of Geopsychrobacter electrodiphilus were isolated (A1 and A2); Strain A1 was determined as the type strain (A1T; ATCC BAA-880T; DSM 16401T; JCM 12469) of the species Geopsychrobacter electrodiphilus and as the type strain of the genus.[1]

In a study on the cultivation of microbial communities in sludge, where sulphate reducers are likely to benefit, the proportion of Geopsychrobacter decreased.[3] An investigation of bacterial diversity in the cold outflow of an iron oxide-tainted plume of saltwater (Blood Falls, Antarctica) indicated about 11% of cells as G. electrodiphilus.[4] The plume were identified as a subglacial “ocean”, where coupled biogeochemical processes below the glacier enable microbes to grow in extended isolation, accumulating iron(II) despite the presence of an active sulfur cycle.[5]

Interaction with Anodes

Holmes et al. 2004 proposed a likely mechanism for a special microbial fuel cell (sediment fuel cell), to support energy with help of G. electrodiphilus and other microbes of a community in marine sediments; based on the article,[1] this imaginary mechanism is summarized here:

  • Some microbes digest complex organic matter (fermentation) in an anaerobic[lower-alpha 2] part of the sediment fuel cell nearby a graphite electrode (anode). G. electrodiphilus grows on the surface of this graphite electrode and oxidize fermentation products, e.g. acetate. Normally, those oxidation processes produce carbon dioxide, protons and electrons and any oxidation has to be coupled to a reduction, because of the electrons. G. electrodiphilus could use a terminal electron acceptor, e.g. poorly crystallized iron(III) oxide (that would be reduced to magnetide) when available. In a sediment fuel cell, G. electrodiphilus has direct contact to the electrode and can use it as a sole electron acceptor. The electrode in the anaerobic part of the sediment fuel cell (anode) has connection to its counterelectrode (cathode) in the overlying aerobic[lower-alpha 3] water. The electrons flow from the anode to the cathode in the overlying aerobic water, where they likely reduce oxygen.

To explain their proposal for the process inside the sediment fuel cell, authors[1] referred to previous investigations.[6][7][8]

Holmes et al. (2004) did not investigate microbial communities or technical devices; the aim of their investigations was to find organisms that transfer electrons to an electrode and to describe them.[1] The G. electrodiphilus strains were able to oxidize acetate, malate, fumarate, and citrate with electron transfer to an electrode poised at +0.52 V (in reference to a standard hydrogen electrode).[1]

One key point of harvesting energy using a sediment fuel cell seems to bridge the anaerobic environment of G. electrodiphilus and the aerobic water; the difference in redox potentials can be used.

Reduction of poorly crystalline Fe(III) oxide results in the formation of magnetite.[1] It is therefore conceivable that the oligodynamic effect in Geopsychrobacter is low and an application with metallic components inside a technical device would be possible.

See also
  • Exoelectrogen

Notes
  1. A new genus and its type species, Geopsychrobacter elctrodipihilus, were effectively published by Holmes et al. (2004, PMID 15466546, DOI:10.1128/AEM.70.10.6023-6030.2004) and both taxa got their authority when Validationlist No. 102 (2005, PMID 15774623, DOI:10.1099/ijs.0.63680-0) was published; see LPSN: Geopsychrobacter.
  2. In this context, “anaerobic” is a place without oxygen. See also “anaerobic organism”/ “aerobic organism”.
  3. In this context, “aerobic” is a place with oxygen. See also “aerobic organism”/ “anaerobic organism”.

References
  1. Holmes DE, Nicoll JS, Bond DR, Lovley DR (October 2004). "Potential role of a novel psychrotolerant member of the family Geobacteraceae, Geopsychrobacter electrodiphilus gen. nov., sp. nov., in electricity production by a marine sediment fuel cell". Applied and Environmental Microbiology. 70 (10): 6023–30. doi:10.1128/AEM.70.10.6023-6030.2004. PMC 522133. PMID 15466546.
  2. Holmes DE, Rotaru AE, Ueki T, Shrestha PM, Ferry JG, Lovley DR (2018). "Electron and Proton Flux for Carbon Dioxide Reduction in Methanosarcina barkeri During Direct Interspecies Electron Transfer". Frontiers in Microbiology. 9: 3109. doi:10.3389/fmicb.2018.03109. PMC 6315138. PMID 30631315.
  3. Zeng GQ, Jia XS, Zheng XH, Yang LP, Sun GP (November 2014). "[Analysis of microbial community variation in the domestication process of sludge in a sulfate-reducing reactor]". Huan Jing Ke Xue= Huanjing Kexue. 35 (11): 4244–50. PMID 25639102.
  4. Mikucki JA, Priscu JC (June 2007). "Bacterial diversity associated with Blood Falls, a subglacial outflow from the Taylor Glacier, Antarctica". Applied and Environmental Microbiology. 73 (12): 4029–39. doi:10.1128/AEM.01396-06. PMC 1932727. PMID 17468282.
  5. Mikucki JA, Pearson A, Johnston DT, Turchyn AV, Farquhar J, Schrag DP, Anbar AD, Priscu JC, Lee PA (April 2009). "A contemporary microbially maintained subglacial ferrous "ocean"". Science. 324 (5925): 397–400. Bibcode:2009Sci...324..397M. doi:10.1126/science.1167350. PMID 19372431.
  6. Bond DR, Lovley DR (March 2003). "Electricity production by Geobacter sulfurreducens attached to electrodes". Applied and Environmental Microbiology. 69 (3): 1548–55. doi:10.1128/AEM.69.3.1548-1555.2003. PMC 150094. PMID 12620842.
  7. Tender LM, Reimers CE, Stecher HA, Holmes DE, Bond DR, Lowy DA, Pilobello K, Fertig SJ, Lovley DR (August 2002). "Harnessing microbially generated power on the seafloor". Nature Biotechnology. 20 (8): 821–5. doi:10.1038/nbt716. PMID 12091916.
  8. Reimers CE, Tender LM, Fertig S, Wang W (January 2001). "Harvesting energy from the marine sediment--water interface". Environmental Science & Technology. 35 (1): 192–5. Bibcode:2001EnST...35..192R. doi:10.1021/es001223s. PMID 11352010.

Further reading
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