National Geographic News

A microscopic image shows bacteria covered in electrically conductive grains.

Image courtesy Souichiro Kato

Charles Q. Choi

for National Geographic News

Published June 8, 2012

Bacteria can use minerals in soil as electrical grids, which helps the microbes generate chemicals they need to survive, a new study says.

The process involves different bacterial species trading electrons—negatively charged subatomic particles.

Electrons are key to all life-forms, from microbes to people. For instance, the human body constantly swaps electrons from one compound to another to help assemble and dismantle vital chemicals, such as natural sugars.

(Related: "Can Sugar Make You Stupid? 'High Concern' in Wake of Rat Study.")

Scientists had known that different species of microorganisms can work together by trading electrons, helping each species process food sources they couldn't otherwise digest easily.

These cooperative interactions were known to happen either via direct contact or by piggybacking electrons on molecules spread through the microbes' surroundings.

But the new work is the first to show that microbes can use conductive minerals as "wires" for boosting their electrical transfers.

"Since microbes have evolved in environments where there exist plenty of conductive mineral particles, it is not surprising that microbes have abilities to utilize mineral particles for various purposes, including electron transfer," said study co-author Kazuya Watanabe, a microbiologist at the Tokyo University of Pharmacy and Life Sciences.

"Electric currents between microbes are very small," he added. "No one gets shocked with electricity in soil."

Microbes Share to Aid Digestion

Watanabe and colleagues investigated two species of soil bacteria, Geobacter sulfurreducens and Thiobacillus denitrificans.

The former bacterium can more easily eat acetate—a common building block of biosynthesis—by ripping electrons off the compound. The latter species can live off the nitrogen-based compound nitrate by adding in electrons.

(Related: "New Bacteria Found on Titanic; Eat Metal.")

In lab experiments, the researchers found that these microbes tended to exchange electrons only after conductive grains of magnetite or hematite were added to their growth solutions.

The conductive minerals were often seen firmly stuck on the surfaces of the bacteria and sometimes were built up as connections between cells.

According to the study team, the findings could explain how bacteria in marine sediments can apparently exchange electrons over centimeters—huge distances for the tiny life-forms.

(Also see "Drug-Resistant Bacteria Found in Four-Million-Year-Old Cave.")

However, it's hard to believe that the conductive grains can transfer electrons over such distances without help, said microbial ecologist Lars Peter Nielsen at Aarhus University in Denmark.

Perhaps the bacteria are somehow actively arranging the grains to serve as electrical conductors, said Nielsen, who did not participate in the new research.

In addition, follow-up research needs to be done to see how bacteria actually use conductive minerals in the wild, said Gemma Reguera, an environmental microbiologist at Michigan State University.

Such work could help improve microbial fuel cells, which use microorganisms to generate electricity from chemical sludge, she said.

The electric bacteria research was detailed online this week in the Proceedings of the National Academy of Sciences.



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