Wired like biology (Image: Steven Puetzer/Getty Images)

IT IS the ultimate in subsea communications: bacteria living in sulphurous mud beneath the seabed respire by transforming themselves into long, insulating cables and shuttling electrons from one to another. This phenomenon has now been imaged for the first time, allowing us to see how some microbes pull off such a feat.

Some bacteria get energy by oxidising the hydrogen sulphide gas in the sediment on the ocean floor. Because there is no oxygen in the sediment to accept the electrons that are produced, bacteria such as Geobacter grow tiny filaments along which the electrons travel until they reach the oxygen in the seawater. This allows the respiration reaction to be completed.

To find out how other bacteria solve this problem, Lars Peter Nielsen of Aarhus University in Denmark and colleagues used an electron microscope to image electrically conducting Desulfobulbus bacteria in sediment samples. They found that individual bacteria, despite being only 3 to 4 micrometres long, are capable of organising themselves into giant power cables made up of several thousand bacteria. These cables can stretch to around 1 centimetre in length, connecting the deepest bacteria living in low-oxygen conditions with those in high-oxygen areas (see diagram).


As the bacterial cells divide, the team found, they remain trapped end to end inside an ever-growing cable made up of their outer membranes. This sheath has internal fibrous ridges running along its length. It is unclear whether these fibres carry the electrons or act as insulation to help the electrons flow more quickly through the cells. Nielsen presented his group’s findings at the American Society for Microbiology’s general meeting in San Francisco this week.

The images show the extent of the bacteria-communications network – a cubic centimetre of sediment can contain up to 1 kilometre of compacted cable. As Desulfobulbaceae can span both the oxygen-poor and oxygen-rich regions of the seabed, the bacterial colony can monopolise sulphide oxidation in the soil, preventing other bacteria from using the resource. “It’s smart evolution,” says Prathap Parameswaran, who studies conducting microbes at Arizona State University in Phoenix.

It’s smart evolution -the electron-carrying wires let the bacteria monopolise the energy resource

The most important question to answer now is how the electrons are carried, says Yuri Gorby of the University of Southern California in Los Angeles. Once researchers understand the physics, they will be able to make “some remarkable biological achievements”, he says, ranging from understanding biogeochemical formations, creating medical devices that mimic the electron transmission, and using the bacteria to clean up contaminated areas.