New Extremeophiles: living on electrons (Introduction)

by David Turell , Friday, September 08, 2017, 22:04 (2633 days ago) @ David Turell

New research:

https://www.quantamagazine.org/electron-eating-microbes-found-in-odd-places-20160621/?u...

"early surveys suggest a potential microbial bounty. A recent sampling of microbes collected from the seafloor near Catalina Island, off the coast of Southern California, uncovered a surprising variety of microbes that consume or shed electrons by eating or breathing minerals or metals.

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"Though eating electricity seems bizarre, the flow of current is central to life. All organisms require a source of electrons to make and store energy. They must also be able to shed electrons once their job is done. In describing this bare-bones view of life, Nobel Prize-winning physiologist Albert Szent-Györgyi once said, “Life is nothing but an electron looking for a place to rest.”

"Humans and many other organisms get electrons from food and expel them with our breath. The microbes that El-Naggar and others are trying to grow belong to a group called lithoautotrophs, or rock eaters, which harvest energy from inorganic substances such as iron, sulfur or manganese. Under the right conditions, they can survive solely on electricity.

"The microbes’ apparent ability to ingest electrons — known as direct electron transfer — is particularly intriguing because it seems to defy the basic rules of biophysics. The fatty membranes that enclose cells act as an insulator, creating an electrically neutral zone once thought impossible for an electron to cross. “No one wanted to believe that a bacterium would take an electron from inside of the cell and move it to the outside,”

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"In the 1980s, Nealson and others discovered a surprising group of bacteria that can expel electrons directly onto solid minerals. It took until 2006 to discover the molecular mechanism behind this feat: A trio of specialized proteins sits in the cell membrane, forming a conductive bridge that transfers electrons to the outside of cell. (Scientists still debate whether the electrons traverse the entire distance of the membrane unescorted.)

"Inspired by the electron-donators, scientists began to wonder whether microbes could also do the reverse and directly ingest electrons as a source of energy. Researchers focused their search on a group of microbes called methanogens, which are known for making methane. Most methanogens aren’t strict metal eaters. But in 2009, Bruce Logan, an environmental engineer at Pennsylvania State University, and collaborators showed for the first time that a methanogen could survive using only energy from an electrode. The researchers proposed that the microbes were directly sucking up electrons, perhaps via a molecular bridge similar to the ones the electron-producers use to shuttle electrons across the cell wall

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"The microbe Spormann studied, Methanococcus maripaludis, excretes an enzyme that sits on the electrode’s surface. The enzyme pairs an electron from the electrode with a proton from water to create a hydrogen atom, which is a well-established food source among methanogens. “Rather than having a conductive pathway, they use an enzyme,” said Daniel Bond, a microbiologist at the University of Minnesota Twin Cities. “They don’t need to build a bridge out of conductive materials.”

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"Spormann and others still believe that methanogens and other microbes can directly suck up electricity, however. “This is an alternative mechanism to direct electron transfer, it doesn’t mean direct electron transfer can’t exist,” .... Spormann said his team has already found a microbe capable of taking in naked electrons. But they haven’t yet published the details.

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"The different varieties of bacteria that Rowe collected thrive under different electrical conditions, suggesting they employ different strategies for eating electrons. “Each bacteria had a different energy level where electron uptake would happen,” Rowe said. “We think that is indicative of different pathways.”

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"Given the bounty from these early experiments, it seems that scientists have only scratched the surface of the microbial diversity that thrives beneath the planet’s shallow exterior. The results could give clues to the origins of life on Earth and beyond. One theory for the emergence of life suggests it originated on mineral surfaces, which could have concentrated biological molecules and catalyzed reactions. New research could fill in one of the theory’s gaps — a mechanism for transporting electrons from mineral surfaces into cells."

Comment: These are amazing organisms which may well offer new approaches to origin of life research. Various forms of electrical charges, like the potassium ions, play major role in living organisms.