Cable bacteria

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Cable bacteria are filamentous bacteria that transport electrons over cm distances and can thus conduct electricity . The electrons are generated during sulfide oxidation in the deeper anoxic sediment and are conducted along the filament to the sediment surface, where oxygen or nitrate are reduced as electron acceptors .

Cable bacteria between two separate sediment layers in a glass cylinder.
The diagram shows the metabolism of cable bacteria in a surface sediment. Hydrogen sulphide (H 2 S) is oxidized in the sulphide-containing layer ("sulphidic sediment") and the electrons (e - ) generated in the process are conducted along the cable bacterial filament to the oxygen-rich sediment layer ("oxic sediment"). Molecular oxygen (O 2 ) is reduced here .

Discovery and occurrence

The process of electron transfer over long distances was discovered in 2010 in an experiment in which the spatially separated sulfide oxidation and oxygen reduction were interrupted and restored. The speed of the measured rates could not be explained by diffusion processes alone . In a later experiment, filamentous bacteria of the Desulfobulbaceae family were identified as the only possible electronic conductors . The electrical conductivity of individual bacterial filaments was later determined by observing the oxidation status of the cytochromes with the aid of Raman microscopy . Since their discovery in marine sediments, cable bacteria have also been detected in a groundwater aquifer and freshwater sediments worldwide. Densities of up to 2 km cable bacterial filaments per square centimeter of sediment surface were detected.

morphology

Cable bacterial filaments have a diameter of 0.4-1.7 µm and lengths of over 1 cm. The individual cells in the filaments are rod-shaped with an average length of 3 µm and 15-58 rib-like ridges that run lengthwise along the entire filament and are arranged around the cells. It is believed that these rib-like structures are related to the electrically conductive properties of cable bacteria. Another special feature of cable bacteria is that, as Gram-negative bacteria, they have two cell-enveloping membranes and each individual cell has its own inner cell membrane in a filament, but the outer cell membrane is divided by all cells in a filament.

Taxonomy

Two Candidatus genera have been described: Electrothrix with four Candidatus species in marine and brackish habitats and Electronema with two Cadidatus species from freshwater sediments. Both genera are classified in the Desulfobulbaceae family. Since cable bacteria are defined by their function rather than their phylogeny , it is possible that more taxa will be discovered in the future.

Ecological importance

Cable bacteria influence the geochemical properties of their environment. They oxidize iron on the sediment surface, creating iron oxides that can bind phosphorus- containing compounds and hydrogen sulfide . This limits the freely available proportion of phosphorus and hydrogen sulfide in the water. Since phosphorus can cause eutrophication and hydrogen sulfide is toxic to many living things, cable bacteria play an important role in maintaining the balance in ecosystems.

application

Cable bacteria have been found in association with benthic microbial fuel cells . These are instruments that can convert chemical energy on the ocean floor into electrical energy . In the future it is conceivable that cable bacteria will be used to increase the efficiency of such microbial fuel cells. Cable bacteria are also related to a bioelectrochemical system for breaking down hydrocarbon contamination in marine sediments. A future application of cable bacteria in bioremediation after oil spills would therefore be conceivable.

distribution

Cable bacteria have been found in various climate zones and ecosystems around the world, including Denmark, the Netherlands, Germany, Japan, Australia and the USA.

References

  1. ↑ Lars Peter Nielsen, Nils Risgaard-Petersen, Henrik Fossing, Peter Bondo Christensen, Mikio Sayama: Electric currents couple spatially separated biogeochemical processes in marine sediment . In: Nature . tape 463 , no. 7284 , 2010, ISSN  0028-0836 , p. 1071-1074 , doi : 10.1038 / nature08790 .
  2. ↑ a b c d e Christian Pfeffer, Steffen Larsen, Jie Song, Mingdong Dong, Flemming Besenbacher: Filamentous bacteria transport electrons over centimeter distances . In: Nature . tape 491 , no. 7423 , November 2012, ISSN  0028-0836 , p. 218–221 , doi : 10.1038 / nature11586 .
  3. ↑ Jesper T. Bjerg, Andreas Schramm, Lars Peter Nielsen, Michael Wagner, Filip JR Meysman, Paula Tataru: Long-distance electron transport in individual, living cable bacteria . In: Proceedings of the National Academy of Sciences . tape 115 , no. 22 , May 29, 2018, ISSN  0027-8424 , p. 5786-5791 , doi : 10.1073 / pnas.1800367115 , PMID 29735671 , PMC 5984516 (free full text) - ( pnas.org [accessed May 9, 2019]).
  4. ↑ a b Hubert Müller, Rainer U. Meckenstock, Tillmann Lueders, Lars Peter Nielsen, Lars Riis Damgaard, Christian Griebler: Long-distance electron transfer by cable bacteria in aquifer sediments . In: The ISME Journal . tape 10 , no. 8 , August 2016, ISSN  1751-7370 , p. 2010–2019 , doi : 10.1038 / ismej.2015.250 , PMID 27058505 , PMC 4939269 (free full text).
  5. ↑ a b Nils Risgaard-Petersen, Lars Peter Nielsen, Andreas Schramm, Lars Riis Damgaard, Lars Schreiber, Daniela Trojan: Cable Bacteria in Freshwater Sediments . In: Appl. Environ. Microbiol. tape 81 , no. 17 , September 1, 2015, ISSN  0099-2240 , p. 6003-6011 , doi : 10.1128 / AEM.01064-15 , PMID 26116678 , PMC 4551263 (free full text) - ( asm.org [accessed May 9, 2019]).
  6. ^ A b Regina Schauer, Lars Peter Nielsen, Andreas Schramm, Bo B. Jørgensen, Jesper J. Tataru Bjerg, Kasper U. Kjeldsen: Succession of cable bacteria and electric currents in marine sediment . In: The ISME Journal . tape 8 , no. 6 , June 2014, ISSN  1751-7370 , p. 1314-1322 , doi : 10.1038 / ismej.2013.239 , PMID 24451206 , PMC 4030233 (free full text).
  7. ↑ a b Sairah Y Malkin, Filip JR Meysman, Henricus TS Boschker, Silvia Hidalgo-Martinez, Eva-Maria Zetsche, Diana Vasquez-Cardenas: Natural occurrence of microbial sulfur oxidation by long-range electron transport in the seafloor . In: The ISME Journal . tape 8 , no. September 9 , 2014, ISSN  1751-7370 , p. 1843–1854 , doi : 10.1038 / ismej.2014.41 , PMID 24671086 , PMC 4139731 (free full text).
  8. ↑ Daniela Trojan, Lars Schreiber, Jesper T.Bjerg, Andreas Bøggild, Tingting Yang, Kasper U. Kjeldsen, Andreas Schramm: A Taxonomic Framework for Cable Bacteria and Proposal of the Candidate Genera Electrothrix and Electronema . In: Systematic and Applied Microbiology . tape 39 , no. 5 , July 2016, ISSN  0723-2020 , doi : 10.1016 / j.syapm.2016.05.006 .
  9. ↑ Fatimah Sulu-Gambari, Dorina Seitaj, Filip JR Meysman, Regina Schauer, Lubos Polerecky: Cable Bacteria Control Iron-Phosphorus Dynamics in Sediments of a Coastal Hypoxic Basin . In: Environmental Science & Technology . tape 50 , no. 3 , February 2, 2016, ISSN  0013-936X , p. 1227-1233 , doi : 10.1021 / acs.est.5b04369 .
  10. ↑ Filip JR Meysman, Caroline P. Slomp, Laurine DW Burdorf, Sairah Y. Malkin, Silvia Hidalgo-Martinez: Cable bacteria generate a firewall against euxinia in seasonally hypoxic basins . In: Proceedings of the National Academy of Sciences . tape 112 , no. 43 , October 27, 2015, ISSN  0027-8424 , p. 13278–13283 , doi : 10.1073 / pnas.1510152112 , PMID 26446670 , PMC 4629370 (free full text) - ( pnas.org [accessed May 9, 2019]).
  11. ^ David L. Correll: The Role of Phosphorus in the Eutrophication of Receiving Waters: A Review . In: Journal of Environment Quality . tape 27 , no. 2 , 1998, ISSN  0047-2425 , p. 261 , doi : 10.2134 / jeq1998.00472425002700020004x .
  12. ↑ Michael Wolf, Paul S. Schrader, Michael F. Graw, Cheng Li, Clare E. Reimers: The Identification of Cable Bacteria Attached to the Anode of a Benthic Microbial Fuel Cell: Evidence of Long Distance Extracellular Electron Transport to Electrodes . In: Frontiers in Microbiology . tape 8 , 2017, ISSN  1664-302X , doi : 10.3389 / fmicb.2017.02055 , PMID 29114243 , PMC 5660804 (free full text).
  13. ↑ Simona Rossetti, Federico Aulenta, Carolina Cruz Viggi, Bruna Matturro: Cable Bacteria and the Bioelectrochemical Snorkel: The Natural and Engineered Facets Playing a Role in Hydrocarbons Degradation in Marine Sediments . In: Frontiers in Microbiology . tape 8 , 2017, ISSN  1664-302X , doi : 10.3389 / fmicb.2017.00952 , PMID 28611751 , PMC 5447156 (free full text).
  14. ↑ Filip JR Meysman, Henricus TS Boschker, Eva-Maria Zetsche, Silvia Hidalgo-Martinez, Lorenz Meire: Long-distance electron transport occurs globally in marine sediments . In: Biogeosciences . tape 14 , no. 3 , February 10, 2017, ISSN  1726-4170 , p. 683-701 , doi : 10.5194 / bg-14-683-2017 .
  15. ^ Daniela Trojan, Lars Schreiber, Jesper T. Bjerg, Andreas Bøggild, Tingting Yang, Kasper U. Kjeldsen, Andreas Schramm: A taxonomic framework for cable bacteria and proposal of thecandidate genera Electrothrix and Electronema. 2016, accessed May 9, 2019 .
  16. ↑ Bridie Smith: Shock as scientists find 'electric' bacteria in the Yarra. December 5, 2014, accessed May 9, 2019 .
  17. ^ Steffen Larsen, Lars Peter Nielsen, Andreas Schramm: Cable bacteria associated with long-distance electron transport in New England salt marsh sediment . In: Environmental Microbiology Reports . tape 7 , no. 2 , 2015, ISSN  1758-2229 , p. 175-179 , doi : 10.1111 / 1758-2229.12216 .