Living electric cables of bacteria
Living electric cables made from bacteria have been discovered on the sea bed.
The weird multi-cellular microbes are one centimetre long and a hundred times thinner than a human hair.
Each one functions as an electric cable containing a bundle of insulated wires - similar to the cables that run power to electric lights and appliances.
Scientists believe they are the source of mysterious electric currents on the ocean floor, identified for the first time nearly three years ago.
The cable bacteria, from the family Desulfobulbaceae, generate electricity by consuming oxygen from seawater.
This is used to power a process that releases energy from sulphur in mud on the sea bed.
Tens of thousands of miles of cable bacteria can live under a single square metre of the ocean floor, say the researchers, whose find is reported in the journal Nature.
Lead scientist Dr Nils Risgaard-Petersen, from Aarhus University in Denmark, said: "The incredible idea that these bacteria should be electric cables really fell into place when, inside the bacteria, we saw wire-like strings enclosed by a membrane."
Colleague Professor Lars Peter Nielsen, also from Aarhus University, said: "On the one hand, it is still very unreal and fantastic. On the other hand, it is also very tangible."
The scientists are now investigating how the cable bacteria function at the molecular level, and their potential role in the Earth's history.