New research uncovers a surprising fact about numerous types of gut bacteria: they can generate electricity.
Electrogenic bacteria are those that are able to produce a certain amount of electricity.
For this reason, ongoing research is looking into ways to use these microorganisms to develop alternative, more sustainable battery-like devices.
So far, electrogenic bacteria have been found in fairly specific natural environments, such as the sediments of various bodies of water.
These environments are typically anaerobic, meaning that they do not contain free oxygen. Now, for the very first time, researchers from the University of California, Berkeley have found that hundred of different bacteria in the human gut are also electrogenic.
These include many types of bacteria, from pathogenic ones that are capable of causing disease, to probiotic bacteria that promote gut health. Yet these gut bacteria produce electricity using a different mechanism than that used by known electrogenic bacteria from other environments.
The researchers — led by Prof. Dan Portnoy — report their important discovery in a study paper that appears in the journal Nature.
A surprising discovery
Prof. Portnoy and team explain that some of the strands of electricity-generating bacteria that they have now identified include Listeria monocytogenes (a common culprit in cases of diarrhea), Clostridium perfringens (which causes gangrene), and Enterococcus faecalis (a pathogen sometimes acquired during hospital stays).
However, numerous other electricity-producing bacteria in the gut are benign. Some of these are probiotics, the researchers observe, while others, such as the Lactobacilli strains, play a role in fermentation.
"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."
Prof. Dan Portnoy
This, he adds, "could tell us a lot about how these bacteria infect us or help us have a healthy gut."
Also, the scientists expect that their unexpected finding may also be helpful in future projects that aim to create microbial fuel cell, an innovative strategy to generate renewable energy.
The researchers explain that bacteria generate electricity as part of their metabolism, in a process that they compare to breathing.
However, whereas organisms such as plants and animals, which live in oxygen-rich environments, use oxygen to aid them in their metabolism, bacteria that reside in anaerobic environments must use other chemical elements.
So, bacteria that reside at the bottom of lakes typically use a mineral, such as iron or manganese, during their complex metabolic process, thereby generating electricity.
Gut bacteria: Electrogenic because it's 'easy?'
However, the electrogenic bacteria found in the gut seem to have a simpler electricity-generating process, and they use an organic compound known as flavin, which is a vitamin B-2 derivative.
"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," explains first study author Sam Light.
"Thus," he says, "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.'"
In collaboration with experts from the Lawrence Berkeley National Laboratory at the University of California, Light and colleagues conducted further tests to see how much electricity these gut bacteria are able to produce.
They found that gut bacteria generate almost as much electricity as other electrogenic bacteria: up to 100,000 electrons per second per cell.
In particular, they were surprised to find that Lactobacillus — a bacterial strand that plays a role in fermentation and is used to make cheese, yogurt, and sauerkraut — has electrogenic properties.
Now, Light and colleagues wonder whether these properties are at all relevant to the taste that Lactobacillus creates in food products obtained through fermentation.
"This is a whole big part of the physiology of bacteria that people didn't realize existed," Light concludes, "and that could be potentially manipulated."