"Very Unreal and Fantastic": Electric Cables Created by Bacteria
Researchers discovered bacteria at the ocean floor that conduct electrons at distances more than a centimeter through elaborate cables.
Publishing in Nature, Danish researchers with American colleagues determined that the seafloor is full of “live wires” that may play an essential role in ocean ecology, if not the ecology of the whole biosphere. These wires are formed by colonies of “novel members of the deltaproteobacterial family Desulfobulbaceae” that effectively form electrical cables, complete with insulation.
A few years ago, these researchers had detected electric currents in the ocean floor. How they were mediated, though, was unknown till now. In the Introduction to their paper, they explained why the current is necessary:
Marine sediments become anoxic because oxygen is consumed by microbial processes at the surface. Without available oxygen the microorganisms living below the surface are supposed to depend on energetically less favourable, anaerobic processes. Recently, however, electric currents have been found to directly connect oxygen reduction at the surface with sulphide oxidation in the subsurface, even when oxygen and sulphide are separated by more than 1 cm. Half of the sediment oxygen consumption can be driven by electrons transported from below. The spatial separation of oxidation and reduction processes invokes steep pH gradients leading to distinct dissolutions and precipitations of minerals. Microbial activity apparently drives the electrochemical half-reactions and the establishment of electron-conducting structures through the sediment.
Science Daily reported on this discovery on Oct. 24, saying that a mystery of electrical conductivity in the seafloor has been solved by the discovery of these bacteria. “They make up a kind of live electric cable that no one had ever imagined existed,” the article said. It quoted one of the researchers’ reactions: “On the one hand, it is still very unreal and fantastic. On the other hand, it is also very tangible,” said Professor at Aarhus University, Lars Peter Nielsen.
Another interesting summary can be found (appropriately) on Wired.com. The article includes six illustrations and photographs of the “marvelous microbes.” Even though they are 1/100 the diameter of the human hair, they have an elaborate structure with 15 to 17 channels down their exteriors that match up from cell to cell, forming a continuous protective sheath, like insulation. Their smallness should not diminish what they accomplish:”Were bacteria the size of humans, the signals would be making a journey 12 miles long.” The fragile cables break easily, but because they are alive, they can grow and regenerate themselves, unlike man-made cables.
A single teaspoon of mud from the seafloor contains at least a half mile of these living cables. Moreover, the researchers found these in sediments from widely distributed samples, suggesting that much of the planet conducts electricity from the anoxic layer to the oxic layer. The electrical charge circuit is completed by ions in seawater, producing water in the process. This has led the researchers to speculate on their role in planetary ecology. In their concluding discussion, they asked follow-up questions and paid a compliment to evolution for creating electrical engineers:
Bacterial micro-cables represent a hitherto unknown lifestyle, which immediately raises many intriguing questions for further research: How are energy conservation and growth allocated among the cells? What is their genetic and metabolic diversity? How are filament division and dispersal controlled? What is the molecular and electronic basis of the electron transport? How widespread are they in nature? Transmission improvement and control of electric currents have been major drivers for electronic innovation. It appears that biological evolution has worked successfully in the same direction.
Wired.com‘s article said, “It’s possible that, at the microbial level, the deep seafloor is humming with current.” The final caption recognized the planetary implications of the living power grid:
With so much electricity being transferred, are other organisms tapping the lines? Might the Desulfobulbaceae be a power source for entire as-yet-unappreciated deep-sea microbial ecologies, which in turn shape some of the planet’s fundamental biogeochemical processes? That’s “an interesting possibility,” said Nielsen, but it’s still speculation.
Less speculatively, the Desulfobulbaceae are definitely breaking down iron sulfides and carbonates in deeper sediment, while generating iron oxide and magnesium calcite at the surface, Nielsen said. The latter are important compounds for life in the oceans above, and ultimately on land. If the new Desulfobulbaceae are as widespread and populous as they seem, they could be an important component of life’s deep-time cycles.
In the Editor’s Summary at Nature.com,the editors added a biomimetic angle to the story:
A major challenge for multicellular organisms is that of supplying every cell with food and oxygen. Nils Risgaard-Petersen and colleagues report a surprising solution to the problem, arrived at by multicelluar filamentous Desulfobulbaceae bacteria several centimetres long, living in the upper layers of marine sediments sampled in Aarhus Bay, Denmark. These organisms seem to function as living electric cables, transporting electrons from sulphides generated in organic matter in deeper anoxic sediments to the oxygen available in the surface layers. These living micro-cables raise a host of topics for future research, and could also find technological applications.
The original paper by researchers at Aarhus University in Denmark was published by Nature on Nov. 8, though posted online on Oct. 24. Finding bacteria that form insulated electrical cables that may play a fundamental role in the ecology of the planet goes to show how much remains to be discovered about the “primitive” microbes surrounding us. Source: Pffefer, Larson et al., “Filamentous bacteria transport electrons over centimetre distances,” Nature 491, 08 November 2012, pp. 218–221, doi:10.1038/nature11586.
It will be interesting to see if similar electrical cabling occurs in other contexts, such as in the soil networks known to connect plants with each other. This intriguing discovery is another example of the empirical trend against evolution: the closer scientists look at the microbial world, the more complex and interconnected it is found to be, and the less plausible the evolutionary just-so stories become. These bacteria appear to exist not only for their own sakes, but also to enable nutrient cycles that affect the whole biosphere. How would the first organisms survive without them? How did they form such elaborate structures? Evolutionists can’t just wave their hands and say they “evolved to” conduct electricity more effectively by transmitting electrons through their interiors, and then “evolved to” add insulating sheaths for “transmission improvement.” No teleology allowed for Darwinists. Their critics can rejoice at here another fine example of sophisticated design, not only in the bacteria themselves, but also in their functional role for their ecology, and possibly the biogeochemical balance of the entire world.