{{short description|Species of bacteria from Desulfobulbaceae family}} thumb|Cable bacteria in between two layers of sediment split apart inside a glass cylinder.|300x300px
'''Cable bacteria''' are filamentous bacteria that conduct electricity across distances over 1 cm in sediment and groundwater aquifers.<ref name="Nielsen2010">{{cite journal | vauthors = Nielsen LP, Risgaard-Petersen N, Fossing H, Christensen PB, Sayama M | title = Electric currents couple spatially separated biogeochemical processes in marine sediment | journal = Nature | volume = 463 | issue = 7284 | pages = 1071–4 | date = February 2010 | pmid = 20182510 | doi = 10.1038/nature08790 | bibcode = 2010Natur.463.1071N | s2cid = 205219761 }}</ref><ref name="Pfeffer2012">{{cite journal | vauthors = Pfeffer C, Larsen S, Song J, Dong M, Besenbacher F, Meyer RL, Kjeldsen KU, Schreiber L, Gorby YA, El-Naggar MY, Leung KM, Schramm A, Risgaard-Petersen N, Nielsen LP | display-authors = 6 | title = Filamentous bacteria transport electrons over centimetre distances | journal = Nature | volume = 491 | issue = 7423 | pages = 218–21 | date = November 2012 | pmid = 23103872 | doi = 10.1038/nature11586 | bibcode = 2012Natur.491..218P | s2cid = 205231198 }}</ref> Cable bacteria allow for long-distance electron transport, which connects electron donors to electron acceptors, connecting previously separated oxidation and reduction reactions.<ref name="Nielsen_2015">{{cite journal | vauthors = Nielsen LP, Risgaard-Petersen N | title = Rethinking sediment biogeochemistry after the discovery of electric currents | journal = Annual Review of Marine Science | volume = 7 | pages = 425–42 | date = 2015 | pmid = 25251266 | doi = 10.1146/annurev-marine-010814-015708 | bibcode = 2015ARMS....7..425N }}</ref> Cable bacteria couple the reduction of oxygen<ref name="Pfeffer2012" /> or nitrate<ref>{{cite journal | vauthors = Marzocchi U, Trojan D, Larsen S, Meyer RL, Revsbech NP, Schramm A, Nielsen LP, Risgaard-Petersen N | display-authors = 6 | title = Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment | journal = The ISME Journal | volume = 8 | issue = 8 | pages = 1682–90 | date = August 2014 | pmid = 24577351 | doi = 10.1038/ismej.2014.19 | pmc = 4817607 | bibcode = 2014ISMEJ...8.1682M }}</ref> at the sediment's surface to the oxidation of sulfide<ref name="Pfeffer2012" /> in the deeper, anoxic, sediment layers.
[[File:Cable diagram.svg|thumb|Diagram demonstrating cable bacteria metabolism in surface sediment. Hydrogen sulfide (H{{sub|2}}S) is oxidized in the sulfidic sediment layer, and the resulting electrons (e<sup>−</sup>) are conducted up through the cable bacteria filament to the oxic layer and used to reduce molecular oxygen (O{{sub|2}}).|333x333px]] ==Discovery== Long-distance electrical conductance in sediment was first observed in 2010 as a spatial separation of sulfide oxidation and oxygen reduction in marine sediment that was interrupted and re-established at a rate faster than could be explained by chemical diffusion.<ref name="Nielsen2010" /> It was later found that this electrical conductance could be observed across a non-conductive layer of glass microspheres, where the only possible conductive structures were filamentous bacteria belonging to the family Desulfobulbaceae.<ref name="Pfeffer2012" />
The conductivity of single, live filaments was later demonstrated by observing the oxidation state of cytochromes using Raman microscopy.<ref name="Bjerg2018">{{cite journal | vauthors = Bjerg JT, Boschker HT, Larsen S, Berry D, Schmid M, Millo D, Tataru P, Meysman FJ, Wagner M, Nielsen LP, Schramm A | display-authors = 6 | title = Long-distance electron transport in individual, living cable bacteria | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 115 | issue = 22 | pages = 5786–5791 | date = May 2018 | pmid = 29735671 | doi = 10.1073/pnas.1800367115 | pmc = 5984516 | bibcode = 2018PNAS..115.5786B | doi-access = free }}</ref> The same phenomenon was later observed in freshwater sediments<ref name="Risgaard-Petersen2015">{{cite journal | vauthors = Risgaard-Petersen N, Kristiansen M, Frederiksen RB, Dittmer AL, Bjerg JT, Trojan D, Schreiber L, Damgaard LR, Schramm A, Nielsen LP | display-authors = 6 | title = Cable Bacteria in Freshwater Sediments | journal = Applied and Environmental Microbiology | volume = 81 | issue = 17 | pages = 6003–11 | date = September 2015 | pmid = 26116678 | doi = 10.1128/AEM.01064-15 | pmc = 4551263 | bibcode = 2015ApEnM..81.6003R }}</ref> and groundwater aquifers.<ref name="Müller2016">{{cite journal | vauthors = Müller H, Bosch J, Griebler C, Damgaard LR, Nielsen LP, Lueders T, Meckenstock RU | title = Long-distance electron transfer by cable bacteria in aquifer sediments | journal = The ISME Journal | volume = 10 | issue = 8 | pages = 2010–9 | date = August 2016 | pmid = 27058505 | doi = 10.1038/ismej.2015.250 | pmc = 4939269 | bibcode = 2016ISMEJ..10.2010M }}</ref> Within a 15 cm thick top layer of sediment, cable bacteria densities providing total length of up to 2 km per square centimeter of surface have been observed.<ref name="Schauer2014">{{cite journal |vauthors=Schauer R, Risgaard-Petersen N, Kjeldsen KU, Tataru Bjerg JJ, B Jørgensen B, Schramm A, Nielsen LP |date=June 2014 |title=Succession of cable bacteria and electric currents in marine sediment |journal=The ISME Journal |volume=8 |issue=6 |pages=1314–22 |doi=10.1038/ismej.2013.239 |pmc=4030233 |pmid=24451206|bibcode=2014ISMEJ...8.1314S }}</ref> thumb|Model representation of a cable bacteria cell<ref>{{Cite journal |last1=Cornelissen |first1=Rob |last2=Bøggild |first2=Andreas |last3=Thiruvallur Eachambadi |first3=Raghavendran |last4=Koning |first4=Roman I. |last5=Kremer |first5=Anna |last6=Hidalgo-Martinez |first6=Silvia |last7=Zetsche |first7=Eva-Maria |last8=Damgaard |first8=Lars R. |last9=Bonné |first9=Robin |last10=Drijkoningen |first10=Jeroen |last11=Geelhoed |first11=Jeanine S. |last12=Boesen |first12=Thomas |last13=Boschker |first13=Henricus T. S. |last14=Valcke |first14=Roland |last15=Nielsen |first15=Lars Peter |date=2018-12-20 |title=The Cell Envelope Structure of Cable Bacteria |journal=Frontiers in Microbiology |volume=9 |article-number=3044 |doi=10.3389/fmicb.2018.03044 |doi-access=free |issn=1664-302X |pmc=6307468 |pmid=30619135}}</ref>|300x300px ==Morphology== Cable bacteria filaments have a diameter of 1–4 μm and lengths of over 1 cm.<ref name=":1">{{Cite journal |last1=Boschker |first1=Henricus T. S. |last2=Cook |first2=Perran L.M. |last3=Polerecky |first3=Lubos |last4=Eachambadi |first4=Raghavendran Thiruvallur |last5=Lozano |first5=Helena |last6=Hidalgo-Martinez |first6=Silvia |last7=Khalenkow |first7=Dmitry |last8=Spampinato |first8=Valentina |last9=Claes |first9=Nathalie |title=Efficient long-range conduction in cable bacteria through nickel protein wires |journal=Nature Communications |date=2021 |volume=12 |issue=1 |article-number=3996 |doi=10.1038/s41467-021-24312-4 |pmid=34183682 |pmc=8238962 |biorxiv=10.1101/2020.10.23.351973 }}</ref> The individual cells in the filaments are rod-shaped with an average length of 3 μm.<ref name="Pfeffer2012" /> As Gram-negative bacteria, they have two cell-enveloping membranes, with each cell having its own individual inner cell membrane, but the outer cell membrane is shared by all cells in a filament.<ref name="Pfeffer2012" /> In the common periplasm there are around 15–60<ref name="Pfeffer2012" /><ref name=":1" /> electron-conducting fibers with a diameter of around 50 nm, which are visible from the outside as parallel, longitudinal ribs. They consist of proteins that are rich in nickel and sulfur, are electrically insulated, and run the entire length of the cell filament.<ref name=":1" />
== Distribution == Cable bacteria are generally found in reduced sediments.<ref name=":02"/> They can be present as a single filament or as an agglomeration of filaments.<ref name=":02">{{cite journal | vauthors = Scholz VV, Müller H, Koren K, Nielsen LP, Meckenstock RU | title = The rhizosphere of aquatic plants is a habitat for cable bacteria | journal = FEMS Microbiology Ecology | volume = 95 | issue = 6 | date = June 2019 | article-number = fiz062 | pmid = 31054245 | doi = 10.1093/femsec/fiz062 | pmc = 6510695 }}</ref> Cable bacteria have been identified as being intertwined with the root hairs of aquatic plants and are present in the rhizosphere.<ref name=":02" /> Their distribution ranges a gradient of salinities; they are present in freshwater, saltwater lakes, and marine habitats.<ref>{{cite journal | vauthors = Trojan D, Schreiber L, Bjerg JT, Bøggild A, Yang T, Kjeldsen KU, Schramm A | title = A taxonomic framework for cable bacteria and proposal of the candidate genera Electrothrix and Electronema | journal = Systematic and Applied Microbiology | volume = 39 | issue = 5 | pages = 297–306 | date = July 2016 | pmid = 27324572 | pmc = 4958695 | doi = 10.1016/j.syapm.2016.05.006 | bibcode = 2016SyApM..39..297T | url = }}</ref><ref>{{cite journal | vauthors = Risgaard-Petersen N, Kristiansen M, Frederiksen RB, Dittmer AL, Bjerg JT, Trojan D, Schreiber L, Damgaard LR, Schramm A, Nielsen LP | display-authors = 6 | title = Cable Bacteria in Freshwater Sediments | journal = Applied and Environmental Microbiology | volume = 81 | issue = 17 | pages = 6003–11 | date = September 2015 | pmid = 26116678 | pmc = 4551263 | doi = 10.1128/AEM.01064-15 | bibcode = 2015ApEnM..81.6003R | veditors = Kostka JE }}</ref> Cable bacteria have been identified in a diverse range of climatic conditions worldwide,<ref name="Burdorf2017">{{cite journal | vauthors = Burdorf LD, Tramper A, Seitaj D, Meire L, Hidalgo-Martinez S, Zetsche EM, etal | date = 2017 | title = Long-distance electron transport occurs globally in marine sediments. | journal = Biogeosciences | volume = 14 | issue = 3 | pages = 683–701 | doi = 10.5194/bg-14-683-2017 | bibcode = 2017BGeo...14..683B | doi-access = free }}</ref> including Denmark,<ref name="Pfeffer2012" /><ref name="Risgaard-Petersen2015" /> the Netherlands,<ref name="Malkin2014">{{cite journal |display-authors=6 |vauthors=Malkin SY, Rao AM, Seitaj D, Vasquez-Cardenas D, Zetsche EM, Hidalgo-Martinez S, Boschker HT, Meysman FJ |date=September 2014 |title=Natural occurrence of microbial sulphur oxidation by long-range electron transport in the seafloor |journal=The ISME Journal |volume=8 |issue=9 |pages=1843–54 |doi=10.1038/ismej.2014.41 |pmc=4139731 |pmid=24671086|bibcode=2014ISMEJ...8.1843M }}</ref> Japan,<ref name="Trojan2016" /> Australia,<ref>{{Cite web | first = Bridie | last = Smith | name-list-style = vanc | work = The Age |url=https://www.theage.com.au/technology/shock-as-scientists-find-electric-bacteria-in-the-yarra-20141205-121751.html|title=Shock as scientists find 'electric' bacteria in the Yarra| date = December 5, 2014 }}</ref> and the United States.<ref name="Larsen2014">{{cite journal | vauthors = Larsen S, Nielsen LP, Schramm A | title = Cable bacteria associated with long-distance electron transport in New England salt marsh sediment | journal = Environmental Microbiology Reports | volume = 7 | issue = 2 | pages = 175–9 | date = April 2015 | pmid = 25224178 | doi = 10.1111/1758-2229.12216 | bibcode = 2015EnvMR...7..175L }}</ref>[[File:Electronema candidate specie.jpg|thumb|''Ca.'' Electronema sp. |300x300px]]
==Motility== Cable bacteria lack flagella, but are capable of gliding motility<ref name=":03" /> by propelling themselves forward through the excretion of substances.<ref name=":0">{{cite journal | vauthors = Kjeldsen KU, Schreiber L, Thorup CA, Boesen T, Bjerg JT, Yang T, Dueholm MS, Larsen S, Risgaard-Petersen N, Nierychlo M, Schmid M, Bøggild A, van de Vossenberg J, Geelhoed JS, Meysman FJ, Wagner M, Nielsen PH, Nielsen LP, Schramm A | display-authors = 6 | title = On the evolution and physiology of cable bacteria | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 116 | issue = 38 | pages = 19116–19125 | date = September 2019 | pmid = 31427514 | pmc = 6754541 | doi = 10.1073/pnas.1903514116 | bibcode = 2019PNAS..11619116K | doi-access = free }}</ref> Cable bacteria have been observed to move as fast as 2.2 μm/s, with an average speed of 0.5 μm/s.<ref name=":03">{{cite journal | vauthors = Bjerg JT, Damgaard LR, Holm SA, Schramm A, Nielsen LP | title = Motility of Electric Cable Bacteria | journal = Applied and Environmental Microbiology | volume = 82 | issue = 13 | pages = 3816–21 | date = July 2016 | pmid = 27084019 | pmc = 4907201 | doi = 10.1128/AEM.01038-16 | bibcode = 2016ApEnM..82.3816B | veditors = Drake HL }}</ref> Speed of motility in cable bacteria is not related to size of the bacteria.<ref name=":03" /> The average distance a cable bacterium glides is approximately 74 μm without interruption.<ref name=":03" />
Cable bacteria filaments tend to bend in half, and their movement is led by the apex of the bend as opposed to leading with one tip of the filament.<ref name=":03" /> Twisting to move through rotational gliding is rare, but does occur.<ref name=":03" />
Cable bacteria likely engage in oxygen chemotaxis, as they are observed to move when in anoxic or hypoxic environments, and cease gliding when contact with oxygen is made.<ref name=":03" /> Although motility is important for other microorganisms, once cable bacteria are located in a place that connects oxygen to sulfide, they no longer need to move.<ref name=":03" /> The reduced need for motility could explain why the cable bacteria genome contains fewer operons related to chemotaxis than other Desulfobulbaceae.<ref name=":0" /> [[File:Interactions between reef-building bivalves and cable bacteria.jpg|thumb|Interactions between reef-building bivalves and cable bacteria<ref>{{Cite journal |last1=Malkin |first1=Sairah Y. |last2=Seitaj |first2=Dorina |last3=Burdorf |first3=Laurine D. W. |last4=Nieuwhof |first4=Sil |last5=Hidalgo-Martinez |first5=Silvia |last6=Tramper |first6=Anton |last7=Geeraert |first7=Naomi |last8=De Stigter |first8=Henko |last9=Meysman |first9=Filip J. R. |date=2017 |title=Electrogenic Sulfur Oxidation by Cable Bacteria in Bivalve Reef Sediments |journal=Front. Mar. Sci. |volume=4 |page=28 |doi=10.3389/fmars.2017.00028 |doi-access=free |bibcode=2017FrMaS...4...28M |issn=2296-7745}}</ref>|300x300px]]
==Taxonomy== The two candidate genera of cable bacteria until now described: ''Electrothrix'' containing four candidate species, found in marine or brackish sediments, and ''Electronema'' containing two candidate species, found in freshwater sediments, seem to be a monophyletic group.<ref name="Trojan2016">{{cite journal | vauthors = Trojan D, Schreiber L, Bjerg JT, Bøggild A, Yang T, Kjeldsen KU, Schramm A | title = A taxonomic framework for cable bacteria and proposal of the candidate genera Electrothrix and Electronema | journal = Systematic and Applied Microbiology | volume = 39 | issue = 5 | pages = 297–306 | date = July 2016 | pmid = 27324572 | pmc = 4958695 | doi = 10.1016/j.syapm.2016.05.006 | bibcode = 2016SyApM..39..297T }}</ref> In 2025 the ''Electrothrix'' genera has added newly described ''Electrothrix yaqonensis'' ''specie''.<ref>{{Cite journal |last1=Hiralal |first1=Anwar |last2=Ley |first2=Philip |last3=van Dijk |first3=Jesper R. |last4=Li |first4=Cheng |last5=Pankratov |first5=Dmitrii |last6=Alingapoyil Choyikutty |first6=Jiji |last7=Pankratova |first7=Galina |last8=Geelhoed |first8=Jeanine S. |last9=Vasquez-Cardenas |first9=Diana |last10=Reimers |first10=Clare E. |last11=Meysman |first11=Filip J. R. |date=2025-04-22 |title=A novel cable bacteria species with a distinct morphology and genomic potential |journal=Applied and Environmental Microbiology |volume=91 |issue=5 |article-number=e02502-24 |language=EN |doi=10.1128/aem.02502-24 |issn=0099-2240 |doi-access=free |pmid=40261324 |pmc=12093952 |bibcode=2025ApEnM..91E2502H }}</ref>
Freshwater and marine cable bacteria have been found to be 88% similar based on 16S ribosomal RNA comparisons.<ref name="Cable Bacteria Take a New Breath Us">{{cite journal |vauthors=Meysman FJ |date=May 2018 |title=Cable Bacteria Take a New Breath Using Long-Distance Electricity |journal=Trends in Microbiology |volume=26 |issue=5 |pages=411–422 |doi=10.1016/j.tim.2017.10.011 |pmid=29174100 |bibcode=2018TrMic..26..411M }}</ref> These genera are classified within the family Desulfobulbaceae, phylum Desulfobacterota.<ref name=":0" /> Cable bacteria are defined by their function rather than their phylogeny, and it is possible that further cable bacteria taxa will be discovered.
==Ecological significance== Cable bacteria strongly influence the geochemical properties of the surrounding environment. Their activity promotes the oxidation of iron at the surface of the sediment, and the resulting iron oxides bind phosphorus-containing compounds<ref name="Sulu-Gambari2016">{{cite journal | vauthors = Sulu-Gambari F, Seitaj D, Meysman FJ, Schauer R, Polerecky L, Slomp CP | title = Cable Bacteria Control Iron-Phosphorus Dynamics in Sediments of a Coastal Hypoxic Basin | journal = Environmental Science & Technology | volume = 50 | issue = 3 | pages = 1227–33 | date = February 2016 | pmid = 26720721 | doi = 10.1021/acs.est.5b04369 | bibcode = 2016EnST...50.1227S | hdl = 1874/329820 | hdl-access = free }}</ref> and hydrogen sulfide,<ref name="Seitaj2015">{{cite journal | vauthors = Seitaj D, Schauer R, Sulu-Gambari F, Hidalgo-Martinez S, Malkin SY, Burdorf LD, Slomp CP, Meysman FJ | display-authors = 6 | title = Cable bacteria generate a firewall against euxinia in seasonally hypoxic basins | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 43 | pages = 13278–83 | date = October 2015 | pmid = 26446670 | doi = 10.1073/pnas.1510152112 | pmc = 4629370 | bibcode = 2015PNAS..11213278S | doi-access = free }}</ref> limiting the amount of phosphorus and hydrogen sulfide in the water. Phosphorus can cause eutrophication, and hydrogen sulfide can be toxic to marine life, meaning that cable bacteria play an important role in maintaining marine ecosystems in coastal areas.
The presence of cable bacteria can lead to a decrease in methane emissions from saturated soils. The transfer of electrons through cable bacteria allows the sulfate reduction that occurs in inundated soils to be balanced by sulfide oxidation. Oxidation is possible because of the release of electrons through the cable bacteria filaments. Through this balance, sulfate remains readily available for sulfate reducing bacteria, which out compete methanogens. This causes a decrease in production of methane by methanogens.<ref>{{cite journal | vauthors = Scholz VV, Meckenstock RU, Nielsen LP, Risgaard-Petersen N | title = Cable bacteria reduce methane emissions from rice-vegetated soils | journal = Nature Communications | volume = 11 | issue = 1 | article-number = 1878 | date = April 2020 | pmid = 32313021 | doi = 10.1038/s41467-020-15812-w | pmc = 7171082 | bibcode = 2020NatCo..11.1878S }}</ref>
==Practical applications== Cable bacteria have been found associated with benthic microbial fuel cells, devices that convert chemical energy on the ocean floor to electrical energy.<ref name="Reimers2017">{{cite journal | vauthors = Reimers C, Li C, Graw M, Schrader P, Wolf M | author-link1=Clare Reimers|title=The Identification of Cable Bacteria Attached to the Anode of a Benthic Microbial Fuel Cell: Evidence of Long Distance Extracellular Electron Transport to Electrodes | journal = Frontiers in Microbiology | volume = 8 | article-number = 2055 | date = 2017 | pmid = 29114243 | doi = 10.3389/fmicb.2017.02055 | pmc = 5660804 | doi-access = free }}</ref> In the future, cable bacteria may play a role in increasing the efficiency of microbial fuel cells deployed in sedimentary environments. Cable bacteria have also been found associated with a bioelectrochemical system that enhances the degradation of marine sediment contaminated by hydrocarbons <ref name="Matturo2017">{{cite journal | vauthors = Matturro B, Cruz Viggi C, Aulenta F, Rossetti S | title = Cable Bacteria and the Bioelectrochemical Snorkel: The Natural and Engineered Facets Playing a Role in Hydrocarbons Degradation in Marine Sediments | journal = Frontiers in Microbiology | year = 2017 | volume = 8 | article-number = 952 | pmid = 28611751 | doi = 10.3389/fmicb.2017.00952 | pmc = 5447156 | doi-access = free }}</ref> and thus may play a role in future oil spill cleanup technologies.
== See also == * Biodegradable electronics * Electric bacteria
== References == {{Reflist}}
== External links == *{{Commons category-inline}}
Category:Microorganisms Category:Bacteria Category:Environmental microbiology Category:Thermodesulfobacteriota