How can electricity be generated from bacteria

Electricity generating bacteria

Bacteria could soon be the power plants of all human beings. Because some of them deal with electricity as naturally as we do with breathing air and bread rolls. Sometimes the rod-shaped unicellular organisms generate electricity during their metabolism, so they breathe it off like people do with carbon dioxide. Sometimes they literally eat it and turn it into high-energy molecules.

Electron breather and electron eater

"We have only known about the electron breather for about a decade, and the electron eater has only been known for a few years," says Alfred Spormann, environmental microbiologist at Stanford University in California. Spormann is one of the pioneers in a completely new field of research: electromicrobiology. He discovered many of these phenomena himself and is now trying to understand what molecular tools make these bacteria such electricity jugglers - and how they can be used for a clean energy system.

On a molecular scale, electricity is made up of migrating electrons. Such electron streams are - as astonishing as it sounds at first - the engine of life: with them all living cells generate energy inside them. Several molecules with an affinity for electrons are connected in series. With every jump of an electron from molecule to molecule, energy is released. For example, cells of plants and animals release electrons from sugar molecules to generate energy and pass them on to oxygen via an electron transport chain.

Electric microbes since the prehistoric times

Until recently, it was thought impossible for organisms to exchange these electrons with their environment. But that is exactly what those bacteria can do in which electromicrobiology is interested. To do this, they have so-called nanowires, for example. These miniature cables consist of cell membranes that are densely covered with electron transport proteins. The negatively charged electrons are passed along the membrane until they land on positively charged metal ions in the surrounding rock.

All known electric microbes come from the first days of life. At that time, there was no oxygen in the earth's atmosphere as a ready-to-use electron collector. So the first living beings had to come up with something else. Just like Shewanella oneidensis: The bacterium now lives in the seabed, where, depending on the location - too much fish droppings, too little light - the oxygen supply can be completely absent. Then it goes the good old way to get rid of its energetically exploited electrons. Via its conductive membrane processes, it uses the iron-rich sediments of the surrounding area as a depository.

Bacteria to generate electricity

This mechanism can be manipulated in such a way that a completely new source of electricity is created: All you have to do is lure the bacterium to the anode of a circuit with an appetizing portion of charge, feed it with sufficient organic material - and the single-cell organism lets plenty of electricity flow. There are many possible applications: Among other things, researchers are working on bacterial batteries and on solutions to generate electricity from human wastewater. Chinese environmental technologists from Hefei, for example, are trying to genetically modify the unicellular organisms so that they carry two different types of electron tunnels next to each other. They want to increase the electrical output of these "microbial fuel cells". Because they are not yet particularly effective. In the laboratory, the idea already works with lactic acid as bacterial feed - the practical test in the sewage treatment plant is still pending.

The other way round is also conceivable: converting electricity into valuable raw materials. Spormann has discovered a particularly promising way to get there in bacteria of the species Methanococcus maripaludis. They live deep in the soil of wet marshland, and it was previously believed that they only feed on carbon dioxide and hydrogen there. Apparently, however, they can also absorb electrons directly in order to make hydrogen themselves. Central to this is a previously unknown protein complex that functions like a drinking straw for electrons. With the help of the absorbed electricity and CO2, Methanococcus ultimately produces methane, i.e. natural gas. "We already have a lot of inquiries from energy companies," says the researcher happily.

Bacteria-based electricity storage

The bacteria could solve a central problem of the energy transition: solar collectors and wind turbines often collect much more electricity than they can put into the grid ad hoc. Millions of euros are simply lost, and the extremely fluctuating power generation also puts a strain on the grids. For this reason, people have been looking for an economical way of storing electricity for a long time. "These bacteria do just that," says Spormann. "And without the energy loss that you have to accept when operating biogas plants or the electrochemical synthesis of hydrogen for similar systems." The yield with which the injected electrons react to methane is over 90 percent.

There is already a company that uses bacteria-based electricity storage. But the bacteria from Electrochaea in Munich cannot be fed directly with electrons. You need hydrogen - which first has to be produced from water using solar power. Energy is lost in the process, and the company states its efficiency is 58 percent. "For me, our integrated system looks like the future," says Spormann confidently.

(bsc)

Comment on the post

Newsletter

Research & technology trends from the upcoming MIT Technology Review at a glance. Appears monthly.