Bacteria grids!

A wide variety of microbes can send electrons into, or accept electrons from, conducting materials. Most organisms internally generate energy by coupling the addition of electrons to one molecule with their removal from another. But some microbes must cooperate to generate the energy for life, swapping molecules or electrons with other species. Research published in Proceedings of the National Academy of Sciences on June 4 suggests the some bacteria do indeed build electricity-conducting grids in the wild.

Microbes use conductive minerals as electric wires for transferring electrons between each other, the team found.

The researchers tested a variety of solutions containing the soil bacteria Geobacter sulfurreducens and Thiobacillus denitrificans, which thrive by eating acetate and nitrate respectively, when they can find a spare electron or two. When the scientists placed either of these microbes alone into a solution containing the two compounds, nothing happened. Nor did the situation improve when both types of microbes were put together into this solution of their favorite foods, suggesting the organisms lacked the ability to directly transfer electrons between them.

But when the scientists added magnetite, an electricity-conducting iron-based mineral, the bacteria got to work eating, cooperating merrily by shuttling electrons back and forth via the magnetite grains. And, although the same effect could be had by adding the rusted red iron mineral hematite, which is a poor conductor, the resulting microbial growth was much smaller and slower (and non-existent when nonconductive aluminum minerals were tried).

Lessons out there for us energy-hungry humans? Meanwhile, here is a question for you: could energy rations be a good option in an energy scarce scenario?