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Electric Dirt is teeming with mysterious new bacteria that could rewrite textbooks

For Lars Peter Nielsen, it all started with the mysterious disappearance of hydrogen sulfide. The microbiologist collected black, smelly mud from the bottom of Aarhus Harbor in Denmark, threw it into large glass beakers and inserted special microsensors that detected changes in the chemical composition of the mud. 

At the beginning of the experiment, the composition was saturated with hydrogen sulfide – a source of odor and color of the sediment. But 30 days later, one strip of dirt turned pale, which indicates the loss of hydrogen sulfide. Eventually, the microsensors showed that the entire connection was gone. Given what scientists knew about the biogeochemistry of mud, recalls Nielsen at Aarhus University, “it didn’t make sense at all.”

The first explanation, he said, was that the sensors were wrong. But the reason turned out to be much more strange: the bacteria connecting the cells create electrical cables that can conduct current up to 5 centimeters through the dirt. 

An adaptation never seen before in microbes allows these so-called cable bacteria to overcome a major problem faced by many organisms living in mud: lack of oxygen. Its absence usually keeps bacteria from metabolizing compounds such as hydrogen sulfide for food. But cables, by binding microbes to oxygen-rich deposits, allow them to react over long distances.

When Nielsen first described the discovery in 2009, his colleagues were skeptical. Philip Meisman, a chemical engineer at the University of Antwerp, recalls thinking, “This is complete nonsense.” Yes, the researchers knew bacteria could conduct electricity, but not at the distances Nielsen suggested. “It was as if our own metabolic processes could affect a distance of 18 kilometers,” says microbiologist Andreas Teske of the University of North Carolina at Chapel Hill.

But the more researchers looked for “electrified” mud, the more they found it in both salt and fresh water. They also identified a second type of dirt-loving electrical microbe: nanowire bacteria, individual cells that grow protein structures that can move electrons over shorter distances. 

These nanowire microbes are found everywhere, including in the human mouth.

Discoveries are forcing researchers to rewrite textbooks; rethink the role of mud bacteria in the processing of key elements such as carbon, nitrogen and phosphorus; and review how they affect aquatic ecosystems and climate change. 

Scientists are also looking for practical applications, exploring the potential of bacteria containing cables and nanowires to combat pollution and power electronic devices. “We are seeing a lot more interactions within microbes and between microbes using electricity,” Meisman says. “I call it the electrical biosphere.”

Most cells thrive by taking electrons from one molecule, a process called oxidation, and transferring them to another molecule, usually oxygen, called reduction. The energy gained from these reactions governs other life processes. In eukaryotic cells, including our own, such “redox” reactions occur on the inner mitochondrial membrane, and the distance between them is tiny – only micrometers. This is why so many researchers have been skeptical about Nielsen’s claim that cable bacteria move electrons through a layer of dirt the size of a golf ball.

Disappearing hydrogen sulfide was the key to proving this. Bacteria make a compound in the mud, breaking down plant debris and other organic materials; in deeper deposits, hydrogen sulfide accumulates due to a lack of oxygen, which helps other bacteria break it down. However, hydrogen sulfide still disappeared in Nielsen’s beakers. Moreover, a rusty tint appeared on the surface of the dirt, which indicated the formation of iron oxide.

Waking up one night, Nielsen came up with a strange explanation: what if bacteria buried in the mud completed the redox reaction, somehow bypassing the oxygen-poor layers? What if, instead, they used the abundant supply of hydrogen sulfide as an electron donor, and then funneled the electrons up towards the oxygen-rich surface? There, in the oxidation process, rust is formed if iron is present.

Finding what carries these electrons has proven difficult. First, Niels Riesgaard-Petersen of Nielsen’s team had to rule out an easier possibility: metal particles in the sediment carry electrons to the surface and cause oxidation. He achieved this by inserting a layer of glass beads, which do not conduct electricity, into a column of dirt. Despite this obstacle, the researchers still found an electric current moving through the mud, suggesting that the metal particles were not conductive.

To see if a cable or wire was carrying electrons, the researchers then used tungsten wire to make a horizontal cut through the mud pillar. The current went out, as if a wire had been cut. Other work narrowed down the size of the conductor, suggesting that it should be at least 1 micrometer in diameter. “This is the usual size of bacteria,” says Nielsen.

Ultimately, electron micrographs revealed a likely candidate: long, thin bacterial fibers that appeared in a layer of glass beads inserted into beakers filled with mud from Aarhus Harbor. Each filament consisted of a stack of cells – up to 2,000 – enclosed in a ribbed outer membrane. In the space between this membrane and the cells stacked on top of each other, a plurality of parallel “wires” stretched the thread over its entire length. The cable-like appearance inspired the common name of the microbe.

Meisman, a former skeptic, was quickly converted. Shortly after Nielsen announced his discovery, Meismann decided to investigate one of his own samples of sea mud. “I noticed the same color changes in the sediment that he saw,” Meisman recalls. “It was Mother Nature’s direction to take it more seriously.”

His team began developing tools and methods for microbial research, sometimes working in conjunction with Nielsen’s group. It was hard going. Bacterial filaments tend to break down quickly after isolation, and standard electrodes for measuring currents in small conductors do not work. But once the researchers learned to pick out a single strand and quickly attach an individual electrode, “we saw really high conductivity,” Meisman says. Live cables can’t compete with copper wires, he said, but they match the conductors used in solar panels and mobile phone screens, as well as the best organic semiconductors.

The researchers also analyzed the anatomy of the cable bacteria. Using chemical baths, they isolated the cylindrical shell, finding that it contained 17 to 60 parallel fibers glued together inside. The shell is the source of conduction, Meisman and colleagues reported last year in Nature Communications. Its exact composition is still unknown, but it may be protein-based.

“It’s a complex organism,” says Nielsen, who now heads the Center for Electro-Microbiology, which was created in 2017 by the Danish government. Among the problems that the center solves is the mass production of microbes in culture. “If we had a pure culture, it would be much easier” to test ideas about cell metabolism and the effect of the environment on conduction, says Andreas Schramm from the center. The cultured bacteria will also make it easier to insulate cable wires and test potential bioremediation and biotechnology applications.

While researchers are puzzling over the bacteria in the cable, others are looking at another big player in electrical mud: nanowire-based bacteria that, instead of folding cells into cables, grow protein wires 20 to 50 nm long from each cell.

As with cable bacteria, the mysterious chemical composition of the deposits led to the discovery of nanowire microbes. In 1987, microbiologist Derek Lovley, now at the University of Massachusetts Amherst, tried to understand how phosphate from fertilizer wastewater – a nutrient that promotes algal blooms – is released from sediment under the Potomac River in Washington, DC. worked and began to weed them out of the dirt. After growing one, now called Geobacter Metallireducens, he noticed (under an electron microscope) that the bacteria had grown bonds with nearby iron minerals. He suspected that electrons were carried along these wires, and eventually figured out that Geobacter orchestrated chemical reactions in the mud, oxidizing organic compounds and transferring electrons to minerals.

Like Nielsen, Lovely faced skepticism when he first described his electrical microbe. Today, however, he and others have registered nearly a dozen types of nanowire microbes, finding them in environments other than dirt. Many carry electrons to and from particles in the sediment. But some rely on other microbes to receive or store electrons. This biological partnership allows both microbes to “engage in new kinds of chemistry that no organism can do alone,” says Victoria Orfan, a geobiologist at the California Institute of Technology. While cable bacteria solve their redox needs by transporting long distances into oxygenated mud, these microbes depend on each other’s metabolism.

Some researchers still debate how bacterial nanowires conduct electrons. Lovley and his colleagues are convinced that the key are chains of proteins called pilins, which are composed of circular amino acids. When he and his colleagues reduced the number of ringed amino acids in the pilin, the nanowires became less conductive. “It was really amazing,” says Lovely, because it is generally accepted that proteins are insulators. But others think that this question is far from being solved. Orphan, for example, says that although “there is overwhelming evidence … I still don’t think [the conduction of the nanowire] is well understood.”

What is clear is that electrical bacteria are everywhere. In 2014, for example, scientists found cable bacteria in three very different habitats in the North Sea: in a tidal salt swamp, in a seabed basin where oxygen levels drop to almost zero at some times of the year, and in a flooded muddy plain near the sea. … Coast. (They didn’t find them in a sandy area populated with worms that churn up sediments and disrupt cables.) Elsewhere, researchers have found DNA evidence of cable bacteria in deep, oxygen-poor ocean basins, hot spring areas, and cold conditions. spills, and mangroves and tidal banks in both temperate and subtropical regions.

Cable bacteria are also found in freshwater environments. After reading Nielsen’s articles in 2010 and 2012, a team led by microbiologist Rainer Meckenstock re-examined sediment cores drilled during a groundwater contamination survey in Düsseldorf, Germany. “We found [the cable bacteria] exactly where we thought we would find them,” at depths where oxygen was depleted, recalls Mekenstock, who works at the University of Duisburg-Essen.

Nanowire bacteria are even more widespread. Researchers have found them in soils, rice fields, deep bowels and even sewage treatment plants, as well as in freshwater and marine sediments. They can exist wherever biofilms are formed, and the ubiquity of biofilms is further evidence of the great role these bacteria can play in nature.

The wide range of electric mud bacteria also suggests that they play an important role in ecosystems. For example, by preventing the build-up of hydrogen sulfide, cable bacteria likely make dirt more habitable for other life forms. Meckenstock, Nielsen, and others have found them on or near the roots of seagrass and other aquatic plants, which release oxygen, which bacteria probably use to break down hydrogen sulfide. This, in turn, protects the plants from the toxic gas. The partnership “seems very characteristic of aquatic plants,” Meckenstock said.

Robert Aller, a marine biogeochemist at Stony Brook University, believes bacteria can also help many underwater invertebrates, including worms that build burrows that allow oxygenated water to enter the mud. He found cable bacteria sticking out from the sides of the worm tubes, presumably so they could use that oxygen to store electrons. In turn, these worms are protected from toxic hydrogen sulfide. “Bacteria make [the burrow] more livable,” says Aller, who described these links in a July 2019 article in Science Advances.

Microbes also alter the properties of dirt, says Saira Malkin, an ecologist at the University of Maryland’s Center for Environmental Sciences. “They’re especially effective … ecosystem engineers.” Cable bacteria “grow like wildfire,” she says; On tidal oyster reefs, she found, One cubic centimeter of mud may contain 2,859 meters of cables that cement the particles in place, possibly making the sediment more resistant to marine organisms.

The bacteria also alters the chemical composition of the dirt, making the layers closer to the surface more alkaline and the deeper ones more acidic, Malkin found. Such pH gradients can affect “numerous geochemical cycles,” including those associated with arsenic, manganese and iron, she said, creating opportunities for other microbes.

Because vast swathes of the planet are covered in mud, the researchers say, bacteria associated with cables and nanowires are likely to have an impact on the global climate. Nanowire bacteria, for example, can take electrons from organic materials such as dead diatoms and then transfer them to other bacteria that produce methane, a powerful greenhouse gas. Under various circumstances, cable bacteria can reduce methane production.

In the coming years, “we will see widespread recognition of the importance of these microbes to the biosphere,” says Malkin. A little over ten years after Nielsen noticed the mysterious disappearance of hydrogen sulfide from the Aarhus mud, he says: “It is dizzying to think about what we are dealing with here.”

Next up: a phone powered by microbial wires?

The pioneers of electrical microbes quickly thought about how to use these bacteria. “Now that we know that evolution has been able to create electrical wires, it would be a shame if we didn’t use them,” says Lars Peter Nielsen, a microbiologist at the University of Aarhus.

One possible application is the detection and control of pollutants. Cable microbes seem to thrive in the presence of organic compounds like oil, and Nielsen and his team are testing the possibility that the abundance of cable bacteria signals the presence of undiscovered pollution in aquifers. The bacteria do not directly degrade the oil, but they can oxidize the sulfide produced by other oily bacteria. They can also help clean up; rainfall recovers faster from crude oil contamination when it is colonized by cable bacteria, another research group reported in January in the journal Water Research. In Spain, a third team is investigating whether nanowire bacteria can accelerate the cleanup of polluted wetlands. And even before the nanowire bacteria were electric,

Electrical bacteria can also give rise to new technologies. They can be genetically modified to alter their nanowires, which can then be cut to form the backbone of sensitive wearable sensors, according to Derek Lovley, a microbiologist at the University of Massachusetts (UMass), Amherst. “We can design nanowires and adapt them to specifically bind compounds of interest.” For example, in the May 11 Lovely issue of Nano Research, UMass engineer Jun Yao and colleagues described a nanowire-based sensor that detects ammonia in concentrations needed for agricultural, industrial, environmental, and biomedical applications.

Created as a film, nanowires can generate electricity from moisture in the air. Researchers believe the film generates energy when a moisture gradient occurs between the top and bottom edges of the film. (The top edge is more exposed to moisture.) As the hydrogen and oxygen atoms of the water separate due to the gradient, charge is generated and electrons flow. Yao and his team reported in Nature on Feb.17 that such a film could create enough energy to light a light-emitting diode, and 17 such devices connected together could power a mobile phone. The approach is “a revolutionary technology for generating renewable, clean and cheap energy,” says Qu Liangti, a materials scientist at Tsinghua University. (Others are more careful noting

Ultimately, the researchers hope to harness the electrical abilities of bacteria without having to deal with picky microbes. Catch, for example, persuaded the common laboratory and industrial bacterium Escherichia coli to make nanowires. This should make it easier for researchers to mass-produce the structures and study their practical applications.

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Science & Technology

20 scientific predictions for the next 10 years

We are lucky to be born and live in an incredible time of development of science and technology. We know the approximate rate of development of both, but we have no idea what this rate will be by the end of our life. Things that have long been considered science fiction are becoming components of our lives every day. In the next ten years, the world may present us with gifts that cannot be refused.

The amazing thing about all these scientific discoveries is that they give rise to technologies that further accelerate technological progress. Our ability to innovate grows exponentially as the years go by. 

To give you an idea of ​​the significance of this progression, here are 20 scientific predictions that should occur by 2030.

1. Artificial intelligence (AI) will pass the Turing test, or in other words, the machine will prove that it can think independently.

2. Hyperloop (Elon Musk’s vacuum train project) will start passenger transportation.

3. Biosensors will go on sale, which will call an ambulance if the wearer suddenly becomes ill. In addition, they will remind you to take certain medications, assessing the current state of the body.

4. The level of air pollution will rise, but scientists will come closer to an effective solution to this global problem.

5. Self-driving car will remain a luxury.

6. The world average cost of solar panels will drop sharply, the transition to solar energy will be very rapid.

7. People will return to the moon and begin its consistent colonization.

8. Robots-killers (drones with weapons) will appear. Crime will reach a fundamentally new level. Investigations will come to a standstill.

9. In developed countries, life expectancy will rise sharply. Cancer will cease to be a fatal problem.

10. NASA’s James Webb Space Telescope will be launched, which will help discover hundreds of new earth-like planets and partially learn the chemical composition of their atmospheres.

11. Rapid development of the multi-billion dollar space tourism industry.

12. In the public domain there will be “sources” for printing clothes on a 3D printer. Tens of millions of workers from poor countries will be left without even this low-paying job.

13. If breast cancer is detected on time, the chance of cure will be 100%.

14. The United States will actively grow organs from stem cells from patients themselves. The donation will in fact be liquidated.

15. We will not find extraterrestrial life on Mars. We will probably find it on the moons of Jupiter or Saturn.

16. SpaceX regularly brings people into lunar orbit in preparation for a manned mission to Mars.

17. Global warming will release the oldest viruses. The Chinese coronavirus will seem like a childish joke.

18. The Internet will completely replace television and print media.

19. Tesla cars will become the world’s best-selling cars.

20. Mass DNA editing experiments will begin. Thanks to this, children will be born with “built-in” protection against a huge number of diseases.

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Designer has created a concept for the electric bike of the future

Futuristic motorcycles have become part of popular culture, associated with the concepts of the near future. They appeared in the film ” Tron: Legacy”, the anime “Akira” and in many video games from the “cyberpunk” genre. Recently, Russian designer Roman Dolzhenko presented his version of the bike of the future.

Russian designer has created a concept for the electric bike of the futureromorwise.com

MIMIC eBike – the concept of an electric superbike – originally existed as a sketch on a paper napkin. Later, the designer made the idea more realistic by rendering in 3DS max.

Minimalism prevails in motorcycle design. It lacks straight lines and protrusions. The dashboard of the bike is completely digital, and consists of a solid display showing basic information (speed and battery charge status).

Superbike MIMICromorwise.com

There are very few details about the superbike. Social network users are most often concerned about the question: how to turn the steering wheel with this design? The front wheel fairing and handlebar structure appear to be inactive. In an interview for InceptiveMind, Dolzhenko answered this question: the front of the motorcycle turns completely, but at a slight angle.

Superbike MIMICromorwise.com

There is no information on the cost of transport, capacity and production, which is not surprising. MIMIC eBike is just an extremely realistic concept art of the motorcycle of the future. Perhaps in a couple of years, some Elon Musk will adapt the MIMIC design for a real electric superbike.

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Genes work differently in men and women

All of our cells have the same genes. They can have mutations, however, both in the muscle cell and in the neuron there is a gene for the globin protein, an insulin gene, an acetylcholinesterase gene, etc. But is it worth reminding that a muscle cell is not like a nerve cell? The point is that genes work differently in different cells.

… although these differences should not be exaggerated – even the end sections of chromosomes, which determine biological age, look the same in men and women.

More than ten years ago, a large international team of researchers launched the GTEx (Genotype-Tissue Expression) project, the goal of which was to determine the activity of all genes in all human tissues and organs. Samples of 49 tissues were taken from 838 donors – dead healthy people, mostly elderly. First of all, the DNA was read from each of the donors. Second, the amount of different RNA was analyzed in each tissue. As you know, genetic information from genes in DNA is first read into the messenger RNA (mRNA) molecule, and then proteins are already synthesized on the mRNA molecule (for simplicity, we are not talking about a large class of RNAs that do not encode proteins and which themselves perform various important functions in the cell). The more active a gene is, the more mRNA is read from it. Therefore, by the level of different mRNAs, one can understand where which genes are more active,

The activity of a gene depends on special regulatory sequences, which are also recorded in the DNA – that is, some sections of DNA affect others. By comparing the genetic text in DNA with the amount of different RNAs in different people, one can understand which regulatory regions in DNA affect a particular gene. Such regions (or loci) in DNA are called eQTL, expression quantitative trait loci, which can be roughly translated as loci that determine the level of activity.

As a result of the work, a whole bundle of fifteen articles was recently published in Science , Science Advances , Cell and other journals. Now, using the map of tissue genetic activity for each gene, you can check how it should work in a particular organ or part of it (because several samples were taken from each organ). On the other hand, by looking for a regulatory region (eQTL) in a person’s genome, one can estimate how certain genes will work. It’s genes – because each regulatory eQTL affects more than two genes.

Another important result concerns telomeres, the ends of chromosomes that shorten with each cell division. Telomeres are often used to assess biological age: the shorter they are, the older the body is. But usually blood cells are taken to measure telomeres. What if different fabrics age differently?

The researchers estimated the length of the end sections of chromosomes in 23 tissues, and came to the conclusion that blood does indeed provide an indication of age in general: telomeres in blood cells shorten in proportion to telomeres in other tissues. At the same time, earlier studies were not confirmed, in which female telomeres were on average longer than male ones – that is, neither women nor men have telomere advantages. Which is curious in its own way, since it is believed that women generally live longer than men . This is probably because telomeres are a significant, but not the only indicator of age. In addition, it was not possible to see a strong shortening of telomeres in smokers (here it is worth noting that lung cancer can occur without telomere shortening).

By the way, about women and men. Gender differences are hard to ignore, and we all know that men and women have different sex chromosomes and that men and women have different hormones. Obviously, this should affect the work of genes. Indeed, researchers have found that 37% of our genes work differently in men and women in at least one tissue. Moreover, some genes, relatively speaking, “work” only in one sex. For example, men with different DPYSL4 gene variants will have different body fat percentages. But in women, the DPYSL4 gene does not affect body fat – this does not mean that the gene does not work, just the amount of adipose tissue depends on other genes. Similarly, in men with different variants of the CLDN7 genethere will be different birth weights. In women, birth weight is linked to another gene, HKDC1 .

Many genes, whose activity depends on sex, are associated with diseases, but their “sex” differences were still unknown. Obviously, this information is useful in personalized therapy, when the patient is being treated according to his individual genetic characteristics. However, the authors of the work note that although a lot of “sex-dependent” genes were found, their activity itself does not change very much. In general, the gender genetic differences between men and women are not very large. We emphasize that this is precisely if we take it as a whole – because the genes on which, say, primary and secondary sexual characteristics depend, work in men and women in very different ways.

What else affects gene activity? For example, age – but here there is a gap in the received data. Above we said that the samples were taken mostly from people in years; in addition, more material is needed to analyze age differences across the entire genome. (By the way, it is possible that sex differences are manifested in different ways at different ages.) Some experts, according to The Scientist portal , generally strongly doubt the reliability of the results, because samples were taken from the dead, and not from living people. On the other hand, where can we find healthy volunteers who would allow them to take a piece of tissue from the bowels of their own brain? Subsequent studies are likely to greatly adjust this map of tissue gene activity, but, one way or another, the new data will have something to compare with.

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