Living power cables discovered

Years ago, Danish scientists from Aarhus University discovered a seemingly inexplicable electric current on the sea floor. Now new experiments have revealed that these currents are mediated by a hitherto unknown type of long, multicellular bacteria that act as living power cables.

The Desulfobulbus bacterial cells, which are only a few thousandths of a millimetre long each, are so tiny that they are invisible to the naked eye. And yet, under the right circumstances, they form a multicellular filament that can transmit electrons across a distance as large as 1 cm as part of the filament’s respiration and ingestion processes.

The discovery was made by scientists at Aarhus University in Denmark and USC and published in Nature on 24 October.

The team studied bacteria living in marine sediments that power themselves by oxidising hydrogen sulfide. Cells at the bottom live in a zone that is poor in oxygen but rich in hydrogen sulfide, and those at the top live in an area rich in oxygen but poor in hydrogen sulfide.

The solution? They form long chains that transport individual electrons from the bottom to the top, completing the chemical reaction and generating life-sustaining energy.

Aarhus and USC researchers collaborated to use physical techniques to evaluate the long-distance electron transfer in the filamentous bacteria. Moh El-Naggar, assistant professor of physics at the USC Dornsife College of Letters, Arts and Sciences, and his colleagues had previously used scanning-probe microscopy and nanofabrication methods to describe how bacteria use nanoscale structures called ‘bacterial nanowires’ to transmit electrons many body lengths away from cells.

“Until we found the cables, we imagined something cooperative where electrons were transported through external networks between different bacteria. It was indeed a surprise to realise that it was all going on inside a single organism,” said Lars Peter Nielsen of the Aarhus Department of Bioscience and a corresponding author of the Nature paper.

“You have feeder cells on one end and breather cells on the other, allowing the whole living cable to survive,” El-Naggar said.