A study published in Nature on Wednesday, September 12, 2018 indicates that a bacterium in our gut is capable of producing electricity. Scientists already knew about the existence of electrogenic bacteria (which produce electricity) in some mines and seabed. Nevertheless, nobody expected to find such bacteria within our gut microbiota.
The microbiota is the set of microorganisms (bacteria, viruses, fungus, yeast…) living in an environment called microbiome. Scientists at the University of California at Berkeley have discovered that the common Listeria monocytogenes that causes diarrhea can also create electricity. The most surprising is that the process used is different from conventional electrogenic bacteria.
While following Listeria monoctyotogenes, the researchers have also observed this phenomenon in other bacteria such as those that cause gangrene most often, nosocomial infections, yoghurt fermentation, as well as various infections (respectively Clostridium perfringens, Enterococcus faecalis, Lactobacilli and pathogenic strains of streptococci)
In general, the bacteria produce electricity in order to be able to eliminate the electrons produced by their metabolism as well as to contribute to the production of energy. Animals and plants, for their part, transfer their electrons to the oxygen (which is the final electron acceptor) present in the mitochondria of each cell (a mitochondrion is an organelle present in each of our cells which produces a significant quantity energy). But the bacteria may be in an oxygen-free environment. They must find another electron acceptor.
Thus, in a geological environment, the electrons will be transferred outside the bacteria to a mineral. The transfer of electrons to a mineral involves a cascade of chemical reactions called the “extracellular electron transport chain”. This chain transports the electrons in the form of a very weak electric current.
The extracellular electron transport of Listeria monocytogenes is much simpler than previously known. The type of transfer that it performs seems only possible for bacteria with a single cell wall. These bacteria are said to be Gram positive. For this transfer to take place, it is necessary that the bacterium is in an environment rich in Flavine which is a derivative of vitamin B2.
Sam Light, lead author of this study, said: “It seems that the cellular structure of these bacteria and the vitamin-rich ecological niche they occupy make electron transfer out of the cell much easier and more cost effective.” He added: “Thus, we believe that conventionally studied mineral bacteria use extracellular electron transfer because it is crucial for their survival, whereas these newly identified bacteria use it because it is ‘easy'”.
To quantify the electricity production of bacteria, the researchers used an electrode that plays the role of electron acceptor. Surveys have shown that the current produced by a bacterium can rise up to 500 microamperes. It produces as much electricity as a conventional electrogenic bacterium.
Professor Dan Portnoy, co-author of the study, states: “the fact that there are so many bacteria that interact with humans, whether as pathogens or in probiotics or in our microbiota or involved in fermentation of human-powered products […] could tell us a lot about how these bacteria infect us or help us have healthy intestines. “