Geopsychrobacter electrodiphilus

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Geopsychrobacter electrodiphilus
Systematics
Class : Deltaproteobacteria
Order : Desulfuromonadales
Family : Geobacteraceae
Genre : Geopsychrobacter
Type : Geopsychrobacter electrodiphilus
Scientific name of the  genus
Geopsychrobacter
Holmes et al. 2005
Scientific name of the  species
Geopsychrobacter electrodiphilus
Holmes , Nicoll , Bond & Lovley , 2005

Geopsychrobacter electrodiphilus is a type of prokaryotic microorganism from the domain of the bacteria . So far it is the only species in the genus Geopsychrobacter .

description

Geopsychrobacter electrodiphilus was isolated from the surface of an anaerobic electrode of a marine sediment fuel cell set up in the laboratory. The sediments from which the strains of Geopsychrobacter electrodiphilus were isolated came from a water depth of 5 meters from Boston Harbor ( Boston Harbor , Massachusetts, near the World's End peninsula ). The name "Geopsychrobacter electrodiphilus" roughly means "electrode-loving rod from cold earth" and alludes to the fact that the microbe comes from the earth (Geo), can cope with the cold (psychro), is rod-shaped (bacter) and was isolated by electrodes ( electrodi), which it colonized voluntarily (philus).

One of two strains was identified as the type strain of the species Geopsychrobacter electrodiphilus and the type strain of the genus (called A1 T ). This strain has been deposited in the American Type Culture Collection (ATCC BAA-880), the German Collection of Microorganisms and Cell Cultures (DSM 16401) and the Japan Collection of Microorganisms (JCM 12470). Geopsychrobacter electrodiphilus , according to Holmes et al. following properties:

The cells do not have pili or flagella and do not form spores . They are immobile, gram-negative curved rods about 2.5 micrometers ( µm ) in length and 0.22 µm in diameter. Geopsychrobacter electrodiphilus can grow at temperatures of only 4 ° C up to 30 ° C, optimally around 22 ° C. It is a strictly anaerobic chemoorganotroph that provides the energy to support growth by coupling the oxidation of acetate or malate to the reduction of Fe (III) , S 0 ( colloidal sulfur ), Mn (IV) or AQDS ( anthraquinone -2,6- disulfonate ). The reduction of Fe (III) can also contribute to the oxidation of aspartic acid , glutamic acid , glycine , alanine , methionine , acetate, succinate , malate, citrate , fumarate , pyruvate , peptone , tryptone , casamino acids , yeast extract , acetoin , ethanol, hydrogen, benzoate or stearate . No growth was observed when lysine , serine , tyrosine , histidine , formate , butyrate , valerate , lactate , propionate , methanol, or nitrilotriacetic acid was provided as an electron donor .

The metabolism of the two strains isolated in parallel differs in that only strain A1 T (i.e. the type strain) can use acetoin, ethanol and hydrogen as electron donors , while only strain A2 can use lactate, propionate and butyrate . Neither of the two tribes could use sulfate , thiosulfate , sulfite, or fumarate as an electron acceptor . Geopsychrobacter electrodiphilus is also able to transfer electrons directly to an electrode. The reduction of iron (III) oxide, which is not very crystalline, leads to the formation of the iron oxide magnetite . The cells contain copious amounts of type c cytochromes .

Systematics

The assignment of Geopsychrobacter to the Geobacteraceae family was based on genetic comparisons of the 16S rRNA genes and other genes ( recA , gyrB , rpoB , nifD and fusA ) . Within the bacteria they belong to the Proteobacteria , there in the δ group ( class Deltaproteobacteria ) and in the order Desulfuromonadales . The current assignment can be viewed in the "List of prokaryotic names with their status in the nomenclature" ( LPSN ) (accessed 2019-02).

Genus:

  • Holmes et al. (2004) - Effective publication on the new genus Geopsychrobacter.
  • IUMS (2005) - validation list number 102, recognition as genus Geopsychrobacter Holmes et al. 2005.

Type:

  • Holmes et al. (2004) - Effective publication on the new species (type species of the genus) Geopsychrobacter electrodiphilus.
  • IUMS (2005) - validation list number 102, recognition as a species (type species of the genus) Geopsychrobacter electrodiphilus Holmes et al. 2005.

meaning

The fact that Geopsychrobacter electrodiphilus operates effectively metabolism at cold temperatures and its ability to colonize carbon electrodes ( graphite electrodes) on its own make it possible to have an impact on the generation of electricity from marine sediments.

According to Holmes et al. (2004) the Geopsychrobacter electrodiphilus strains A1 T and A2 could grow if a graphite electrode was provided as the only electron acceptor. Both strains were able to oxidize several organic acids (acetate, malate, fumarate and citrate) with simultaneous electron transfer to an electrode ( potential of +0.52 V with respect to a standard hydrogen electrode ). When strain A1 T was grown with acetate (0.55 mM) as an electron donor and an electrode as an electron acceptor, 90.2% of the electrons available in the complete oxidation of acetate to CO 2 were transferred to the electrode, so that current could be generated (maximum current 3.73 mA / cm 2 ). Furthermore, current was generated by the strain A1 T (~ 8.89 mA / cm 2 ) when fumarate (2.07 mM) was provided as an electron donor and an electrode was the only electron acceptor (96.3% yield for the electrons).

Technical applications have not yet grown from the potential of Geopsychrobacter electrodiphilus . It should be noted that although the isolation of the two strains was due to the microbes being scraped off the graphite electrodes, this was preceded by enrichment with colloidal iron (III) oxide. Geopsychrobacter electrodiphilus can use a graphite electrode as an electron acceptor, but has alternatives that it should also prefer to use. The stoichiometry of the acetate utilization was determined with amorphous iron (III) oxide as the only electron acceptor during growth: CH 3 COO - + 8 Fe 3+ + 4 H 2 O → 2 HCO 3 - + 8 Fe 2+ + 9 H + .

Furthermore, substances are also decisive for the occurrence of a microbe which, in contrast to competing species and strains, it cannot utilize. In a study on the cultivation of microbial communities in mud, in which sulphate reducers are likely to have advantages, the proportion of Geopsychrobacter decreased.

The aim of the studies by Holmes et al. was to find microbes that can transfer electrons to an electrode and describe it; the investigation of microbial communities or technical devices was not in the foreground. Nevertheless, the authors speculate how a marine sediment fuel cell (a special, microbial fuel cell ) might work to generate energy using G. electrodiphilus in a microbial community. These ideas are based on previous studies and are summarized here:

  • Some microbes digest complex organic matter ( fermentation ) in an anaerobic part of the marine sediment fuel cell near a graphite electrode ( anode ). G. electrodiphilus grows on the surface of this graphite electrode and oxidizes the fermentation products, e.g. B. acetate . Normally such oxidation processes produce carbon dioxide , protons and electrons , each oxidation having to be coupled with a reduction because of the electrons. G. electrodiphilus could use a terminal electron acceptor, if available, e.g. B. Little crystallized iron (III) oxide , which would be reduced to magnetite . In a fuel cell, G. electrodiphilus has direct contact with the electrode and can use it as its only electron acceptor . The anode colonized by G. electrodiphilus in the anaerobic part of the marine sediment fuel cell has a connection to its counter electrode ( cathode ) in the aerobic water above . The electrons flow from the anode to the cathode, where oxygen as the terminal electron acceptor is reduced on the cathode surface (and water is produced).

An important point in generating energy with the help of a marine sediment fuel cell seems to be the connection of the anaerobic environment of G. electrodiphilus with the aerobic water, so that the difference in redox potentials can be used without the oxygen, which is toxic to anaerobic microbes , reaching it.

On the basis of Geopsychrobacter electrodiphilus , the question of the extent to which potentially extraterrestrial , organic substances, here non-proteinogenic amino acids , could have influenced the development of anaerobic iron reducers was also brought into the focus of an investigation . It was shown that some of these substances are toxic even in low concentrations .

Databases

Individual evidence

  1. ↑ a b c IUMS: Validation List No. 102: Validation of publication of new names and new combinations previously effectively published outside the IJSEM. In: International Journal of Systematic and Evolutionary Microbiology 55, 2005, p. 547, doi: 10.1099 / ijs.0.63680-0 .
  2. ↑ a b c d e f g h i j k l m Dawn E. Holmes, Julie S. Nicoll, Daniel R. Bond, Derek R. Lovley: 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. In: Appl. Environ. Microbiol. tape 70 , no. 10 , October 1, 2004, p. 6023-6030 , doi : 10.1128 / AEM.70.10.6023-6030.2004 .
  3. ↑ LPSN in collaboration with Ribocon GmbH: Classification of domains and phyla - Hierarchical classification of prokaryotes (bacteria), Version 2.1. Updated 19 July 2018. In: LPSN, List of prokaryotic names with standing in nomenclature. JP Euzéby, July 2018, accessed February 2019 .
  4. ↑ GQ Zeng, XS Jia, XH Zheng, LP Yang, GP Sun: [Analysis of microbial community variation in the domestication process of sludge in a sulfate-reducing reactor]. In: Huan jing ke xue = Huanjing kexue. Volume 35, Number 11, November 2014, pp. 4244-4250, PMID 25639102 .
  5. ^ DR Bond, DR Lovley: Electricity production by Geobacter sulfurreducens attached to electrodes. In: Applied and Environmental Microbiology. Volume 69, Number 3, March 2003, pp. 1548-1555, PMID 12620842 , PMC 150094 (free full text).
  6. ↑ LM Tender, CE Reimers, HA Stecher, DE Holmes, DR Bond, DA Lowy, K. Pilobello, SJ Fertig, DR Lovley: Harnessing microbially generated power on the seafloor. In: Nature Biotechnology . Volume 20, Number 8, August 2002, pp. 821-825, doi: 10.1038 / nbt716 , PMID 12091916 .
  7. ^ CE Reimers, LM Tender, S. Ready, W. Wang: Harvesting energy from the marine sediment-water interface. In: Environmental science & technology. Volume 35, Number 1, January 2001, pp. 192-195, PMID 11352010 .
  8. ↑ SL Nixon, CS Cockell: Nonproteinogenic D-amino acids at millimolar concentrations are a toxin for anaerobic microorganisms relevant to early Earth and other anoxic planets. In: Astrobiology. Volume 15, number 3, March 2015, pp. 238–246, doi: 10.1089 / ast.2014.1252 , PMID 25695622 .