Biology

Electric bacteria found in the human gut

An artist's rendition of Listeria bacteria, which have been found to produce electricity
An artist's rendition of Listeria bacteria, which have been found to produce electricity
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An artist's rendition of Listeria bacteria, which have been found to produce electricity
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An artist's rendition of Listeria bacteria, which have been found to produce electricity
A "battery" made by tapping into the electrogenic bacteria
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A "battery" made by tapping into the electrogenic bacteria

The diverse microbes that live in our gut keep turning up new surprises. In recent years this tiny ecosystem has been found to influence our health in some pretty profound ways, and different species have been implicated in all kinds of diseases throughout the body. But now researchers at UC Berkeley have found that some species of gut-dwelling bacteria can generate electricity.

Electric bacteria have been known about for quite a while, but this is the first time they've been found in the human body. Normally, these little lightning bugs reside in lakes, soil, around hydrothermic vents and particularly in acidic environments. We've even put them to work helping us ferment cheese, yoghurt and alcohol, purify water, and make batteries.

Among the gut bacteria found to be electrogenic were species like Listeria monocytogenes, Clostridium perfringens, Enterococcus faecalis, streptococcus and Lactobacilli. This motley crew is mostly pathogenic, responsible for food-borne illnesses, diarrhea, gangrene, hospital-acquired infections and even miscarriages. Lactobacilli, meanwhile, is a probiotic, often found in yogurt.

"The fact that so many bugs that interact with humans, either as pathogens or in probiotics or in our microbiota or involved in fermentation of human products, are electrogenic – that had been missed before," says Dan Portnoy, an author of the study. "It could tell us a lot about how these bacteria infect us or help us have a healthy gut."

But it's not just a matter of finding new tricks in old bacteria – these species were found to use a completely different mechanism to previously-known electrogenic bacteria. Electrons produced in cells through metabolism need to be removed, and while we air-breathing creatures use our friend oxygen, electrogenic bacteria have developed a way to "breathe" minerals like iron or manganese. A series of chemical reactions use those minerals to carry electrons out of the cells, which takes the form of a tiny electrical current.

A "battery" made by tapping into the electrogenic bacteria
A "battery" made by tapping into the electrogenic bacteria

The electric gut bacteria have been found to use a much simpler "electron transfer chain" than others. Instead of iron or oxygen, these bacteria seem to be able to use flavin molecules – derivatives of vitamin B2 – when they are plentiful in the environment around them. And it's only been seen so far in gram-positive bacteria – those with a single cell wall – which should make electron transfer easier than in species with two cell walls.

"It seems that the cell structure of these bacteria and the vitamin-rich ecological niche that they occupy makes it significantly easier and more cost effective to transfer electrons out of the cell," saysSam Light, first author of the study. "Thus, we think that the conventionally studied mineral-respiring bacteria are using extracellular electron transfer because it is crucial for survival, whereas these newly identified bacteria are using it because it is 'easy.'"

Using an electrode, the team measured the strength of the electric current that these bacteria produce, and found it to be up to 500 microamps. That puts them on an equal footing with other known electrogenic bacteria.

The discovery could lead to new ways to manipulate gut bacteria to improve our health or fight disease – or just make tastier cheese or yogurt.

The research was published in the journal Nature.

Source: UC Berkeley

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