[ad_1]
Researchers at the University of California (UC) in Berkeley said they discovered a bacterium that frequently causes diarrhea Listeria monocytogenes, produces electricity using an entirely different method of known electrogenic bacteria, and that hundreds of other bacterial species use this same process. Their study ("An extracellular electron transfer mechanism based on flavins in various Gram-positive bacteria"), published online in Nature, will be good news for those currently trying to create live batteries from microbes. These "green" bioenergy technologies could, for example, generate electricity from bacteria in waste treatment plants.
"Extracellular electron transfer (EET) describes microbial bioelectrochemical processes in which electrons are transferred from the cytosol to the outside of the cell. Mineral-releasing bacteria use elaborate electron transfer mechanisms based on heme, but the existence and mechanical basis of the other TSEs remains largely unknown. Here we show that the pathogen of food origin Listeria monocytogenes uses a distinctive flavine EET mechanism to deliver electrons to iron or an electrode. By performing a genetic screen before to identify L. monocytogenes mutants with reduced extracellular activity of ferric iron reductase, we identified an eight-gene locus responsible for EET. This locus encodes a specialized NADH dehydrogenase that separates EET from aerobic respiration by channeling electrons to a discrete pool of quinones located on the membrane. Other proteins facilitate the assembly of an abundant extracellular flavoprotein which, coupled with flavin shuttles of free molecules, mediates the transfer of electrons to extracellular acceptors, "the researchers write.
"This system thus establishes a simple electron path consistent with the unique membrane structure of the Gram-positive cell. The activation of EET promotes growth on non-fermentable carbon sources and a mutant EET exhibits a defect of competition in the gastrointestinal tract of the mouse. Orthologues of the genes responsible for EET are present in hundreds of Firmicutes phylum species, including many pathogens and commensal members of the gut microbiota, and correlate with EET activity. in the strains analyzed. These results suggest a greater prevalence of EET-based growth capacities and establish a previously underestimated relevance for electrogenic bacteria in various environments, including host-associated microbial communities and infectious diseases.
Many of these sparkling bacteria are part of the human intestinal microbiome, and many, like the virus responsible for listeriosis, a foodborne illness, which can also cause miscarriages, are pathogenic. The bacteria that cause gangrene (Clostridium perfringens) and nosocomial infections (Enterococcus faecalis) and some pathogenic streptococcal bacteria also produce electricity. Other electrogenic bacteria, like lactobacilli, are important in the fermentation of yogurt, and many are probiotics.
"The fact that so many bugs that interact with humans, whether as pathogens or in probiotics or in our microbiota or involved in the fermentation of human products, are electrogenic – this had been forgotten before," says Dan Portnoy, Dr. UC Berkeley, Professor of Molecular and Cell Biology and Plant and Microbial Biology: "That could tell us a lot about how these bacteria infect us or help us have a healthy gut."
The bacteria generate electricity to eliminate the electrons produced during the metabolism and to promote the production of energy. While animals and plants transfer their electrons to oxygen inside each cell's mitochondria, bacteria in oxygen-free environments, including our guts, but also alcoholic and cheese fermentation tanks and the acid mines must find another electron acceptor. In geological environments, it was often a mineral, for example iron or manganese, outside the cell. In a sense, these bacteria "breathe" iron or manganese.
The transfer of electrons out of the cell to a mineral requires a cascade of special chemical reactions, the extracellular electron transfer chain, which transports the electrons in the form of a tiny electrical current. Some scientists have used this chain to make a battery: stick an electrode in a bottle containing these bacteria and you will be able to generate electricity.
The newly discovered extracellular electron transfer system is actually simpler than the already known transfer chain, and appears to be used by bacteria only when necessary, perhaps when oxygen levels are down, according to the research team. Until now, this simpler electron transfer chain has been found in single cell walled bacteria – microbes classified as Gram-positive bacteria – that live in a flavin-rich environment, derived from the vitamin B2.
"It seems that the cellular structure of these bacteria and the vitamin-rich ecological niche they occupy make it much easier and more cost-effective to transfer the electrons from the cell," says Sam Light, the postdoctoral author. companion. "Thus, we believe that the classically studied mineral-breathing bacteria use extracellular electron transfer because it is crucial for survival, whereas these newly identified bacteria use it because they are" easy "."
To see how robust this system is, Dr. Light is associated with Caroline Ajo-Franklin, Ph.D., a scientist at the Lawrence Berkeley National Laboratory, who explores the interactions between living microbes and inorganic materials for applications. possible in carbon capture and sequestration. and production of bio-solar energy. She used an electrode to measure the electrical current flowing from the bacteria (up to 500 microamperes), confirming that it is actually electrogenic. In fact, they produce about as much electricity – about 100,000 electrons per second per cell – as the known electrogenic bacteria.
Dr. Light is particularly intrigued by the presence of this system in Lactobacillus, essential bacteria for the production of cheese, yoghurt and sauerkraut. Perhaps, he suggests, the transport of electrons plays a role in the taste of cheese and sauerkraut.
"It's a big part of the physiology of bacteria that people do not realize and that could be manipulated," he says.
Drs. Light and Portnoy have many more questions about how and why these bacteria have developed such a unique system, for example simplicity, it is easier to transfer electrons through a cell wall than by two, and to take advantage of the flavin molecules the electrons seem to have allowed these bacteria to find a way to survive in oxygen-rich and oxygen-poor environments.
[ad_2]
Source link
