bacteria drive electric mud

The Scientist | Underwater mud can conduct electricity, possibly with the help of bacteria in the sediment -- a result that helps explain the large amount of electrical activity researchers have detected in ocean sediments, a study published in this week's in Nature reports.

The finding could change how researchers think about microbes' contributions to geochemical processes.

"It's an interesting and important contribution," said Dirk de Beer from the Max Planck Institute for Marine Microbiology, who was not involved in the study. The findings show that processes crucial for life in underwater environments, such as oxidation and reduction reactions, "run faster than we think they can, and in places where we don't expect them," said de Beer.

Researchers made the discovery, because, like many great scientist, they got lazy about cleaning their petri dishes, said lead author Lars Peter Nielsen from Aarhus University in Denmark. "We had some stinky mud standing in the lab," said Nielsen, and they noticed that the sulfides -- "the stinky part" in the upper centimeter of the mud -- changed color over time, indicating that the sulfide had been oxidized. Sulfides are present in mud that lacks oxygen, which should have been true of all the mud in Nielsen's petri dish save that at the very surface, and yet as far as a centimeter down, the sulfur had been converted into elemental sulfur -- a process that requires an electron acceptor like oxygen.

When they depleted oxygen from the surface water, sulfide levels in the mud rose, and when oxygen was bubbled back into the water, the sulfide levels dropped. Oxygen can't diffuse into the mud as quickly as this fluctuation took place; instead, the researchers showed a link between this change and the movement of electrons.

Nielsen and his colleagues believe that conductance is driven by bacteria stratified in different layers of the sediment. The bacteria at the surface, with access to oxygen, respire, consuming the electrons. Those electrons are produced by the bacteria in the sulfur rich lower sediments as they convert food into energy. "One will eat, the other will breathe and together they will share the energy," said Nielsen. Fist tap Dale.