Once again, laziness pays off. When microbiologist Lars Peter Nielsen and his team were studying marine sediments, they got a little sloppy about cleaning their beakers. But after letting samples sit around in the lab for a few weeks, they began to see weird chemical patterns in them that you just wouldn’t expect. As they saw changes in the surface of the mud quickly trigger other changes down below, the scientists came upon a startling idea: that the bacteria in the top layer and those deep down were somehow electrically linked. Their paper appears this week in Nature.
Specifically, Nielsen saw that hydrogen sulfide buried below the sediment’s surface (the stuff that makes it smell bad) was oxidizing and changing color. One problem, though: That shouldn’t be happening. Below the sediment surface there is plenty of hydrogen sulfide and carbon for bacteria to consume via oxidation, or removing electrons [Scientific American]. But the reaction can’t be sustained without access to dissolved oxygen, which carries away electrons produced by the reaction, and in these samples the oxygen was all up at the sediment’s surface. So the researchers hypothesize that the buried bacteria form a conductive chain to ferry the electrons up to the surface.
At first the team tried alternative explanations, but none seemed to fit. The distance was so great, and the response time so quick, that usual methods of chemical transport — molecular diffusion, or a slow drift from high to low concentration — couldn’t explain it [Wired.com]. For him, only the electrical linkage could explain a connection between bacteria separated by as much as a half inch (if you compare distance to body size, that half inch for a bacterium feels like what 12 miles would feel like to us humans).
How is this even possible? Researchers recently discovered that some bacteria have so-called nanowires, hair-like extensions on the cells’ surface that can conduct electricity. Nielsen and his colleagues speculate that these nanowires are responsible for conducting the electrons [The Scientist]. However, those tiny wires don’t explain how the connection bridges such great distances (in bacterial terms). Researchers outside the study told The Scientist that pyrite grains embedded in the mud could aid conductivity, or that some yet to be discovered mechanism is responsible.
The discovery has raised comparisons to the biological networks that wire the forest in the 3D blockbuster Avatar, and Nielsen admits it’s pretty cool. “One of my colleagues saw this, and immediately sent me a message: ‘You’ve discovered the secret of Avatar! Go see it!’ The similarities are quite striking” [Wired.com].
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Image: Nils Risgaard-Petersen