Research from CEM: Laser light maps electrons’ way through cable bacteria

23. May 2018

Using laser light, researchers from the Center for Electromicrobiology (CEM) at Aarhus University examined the loss of voltage in the newly discovered cable bacteria. The study was recently published in the journal PNAS.

A single cable bacteria filament about 1 centimenter long. (Foto: Jesper Tataru Bjerg)

Head of center Lars Peter Nielsen, Professor Andreas Schramm, and Ph.D. student Jesper Tataru Bjerg, from the Center for Electromicrobiology (CEM) at Aarhus University, in collaboration with researchers from Austria and the Netherlands, have used laser light to examine the loss of voltage in the peculiar electric bacteria called cable bacteria.

Cable bacteria are around one centimeter long, are shaped like thin threads, and consist of thousands of cells surrounded by a joint outer cape with electric wires. The life form lives on the bottoms of seas, lakes, and streams and was discovered approximately seven eight ago by head of center Lars Peter Nielsen and colleagues. The cable bacteria transport electrons from the oxygen-free mud on the bottom of the sea up to the mud’s surface that is rich with oxygen, only a few centimeters higher. In that way, the cable bacteria are able to eat at one end and breathe at the other, an ability that is unique.

Around eight years ago, Professor Lars Peter Nielsen and his research team discovered the living electric “cables” on the bottom of Aarhus Bay. In the video, hundreds of cable bacteria are shown, appearing in the bottom of the sediment and moving upward in an attempt to find oxygen. (Video: Aarhus University)

Through laser spectrometry, in this case the so-called Raman spectroscopy, the researchers have used laser light to examine the molecules of the bacteria and to measure their energy levels. With laser light, the researchers can investigate the bacteria’s transportation of electrons over millimeter-wide distances, the biggest distance measured in a living organism so far. From the measurements, the researchers can also calculate a loss of voltage in every single cable bacterium. In that way, they can measure how far the bacteria can go in the oxygen-free seabed without losing their ability to transport electricity.

“They’ll be in trouble if they stretch further than 3 cm downwards into the sediment. In principle, the individual bacteria can be longer than 3 cm, but then they must meander up and down, so that they alternate between the oxygen-rich and oxygen-free environments in the sediment,” explained Professor Schramm to Aarhus University.

As part of the experiment, the research team removed the end of the cable bacteria that releases oxygen to the surface and thereby created a sort of power cut in the microscopic form of life. The result was that the bacteria’s ability to transport the electrons decreased drastically in the remaining part of the bacteria.

“Our measurements showed the lowest potential in the cells at the end where electrons from the food source were being loaded, and the highest potential at the opposite end, where the electrons were being unloaded to oxygen,” Nielsen said to Aarhus University and adds:

“This is the first time that electron transport has been demonstrated in individual cable bacteria,” Nielsen said to Aarhus University.

Read more about the research at Aarhus University here

The scientific article can be found at PNAS here