Standoffish electrons typically keep one another at arm’s length, repelling their neighbors. But surprisingly, under certain circumstances, this repulsion can cause pairs of electrons to soften their stance toward one another and attract instead, new research shows. The effect may be the key to someday producing a new type of high-temperature superconductor, scientists report in the July 21 Nature.
Though the effect was first predicted over 50 years ago, previous attempts to coerce electrons to behave in this chummy way have failed. Like charges repel, so negatively charged electrons ordinarily rebuff one another. But now researchers have validated the counterintuitive idea that an attraction between electrons can emerge. “Somehow, you have [this] magic that out of all this repulsion you can create attraction,” says study coauthor Shahal Ilani, a physicist at the Weizmann Institute of Science in Rehovot, Israel. Ilani and colleagues produced the effect in a bare-bones system of electrons in carbon nanotubes. Operating at temperatures just above absolute zero, the system is made up of two perpendicular carbon nanotubes — hollow cylinders of carbon atoms — about 1 nanometer in diameter.
Two electrons sit at sites inside the first nanotube. Left to their own devices, those two electrons repel one another. A second nanotube, known as the “polarizer,” acts as the “glue” that allows the two electrons to attract. When the scientists brought the two nanotubes close together, says Ilani, “the electrons in the first nanotube changed their nature; they became attractive instead of repulsive.”
This flip is due to the nature of the polarizer. It contains one electron, which is located at one of two sites in the carbon nanotube — either between the first nanotube’s pair of electrons or farther away. The pair of electrons in the first nanotube repels the polarizer’s electron, kicking it from the near to the far site. And the electron’s absence leaves behind a positively charged vacancy, which attracts the pair of electrons toward it — and toward each other. It’s a “tour de force,” says Takis Kontos, a physicist at the École Normale Supérieure in Paris, who wrote a commentary on the paper in the same issue of Nature. Although the system the scientists created is very simple, he says, “the whole experiment built around it is extremely complex.” Electrons are known to attract in certain situations. In conventional superconductors, electrons pair up due to their interactions with ions in the material. This buddy system allows superconductors to conduct electricity without resistance. But such superconductors must be cooled to very low temperatures for this effect to occur.
But in 1964, physicist William Little of Stanford University theorized that electron pairs could likewise attract due to their interactions with other electrons, instead of ions. Such pairs should stay linked at higher temperatures. This realization sparked hopes that a material with these attracting electrons could be a room-temperature superconductor, which would open up a wealth of technological possibilities for efficiently transmitting and storing energy.
It’s yet to be seen whether the effect can produce a superconductor, and whether such a superconductor might work at higher temperatures — the new discovery shows only that the attraction can occur due to electrons’ repulsion. It’s “the first important step,” says Ilani. Now, scientists can start thinking of how to build “interesting new materials that are very different than what you can find in nature.”
U.S. drivers love to hit the road. The problem is doing so safely.
In 2013, 32,894 people in the United States died in motor vehicle crashes. Although down since 2000, the overall death rate — 10.3 per 100,000 people — tops 19 other high-income countries, the U.S. Centers for Disease Control and Prevention reported July 8. Belgium is a distant second with 6.5 deaths per 100,000. Researchers reviewed World Health Organization and other data on vehicle crash deaths, seat belt use and alcohol-impaired driving in 2000 and 2013. Canada had the highest percentage of fatal crashes caused by drunk drivers: 33.6 percent. New Zealand and the United States tied for second at 31 percent. But Canada and 16 other countries outperformed the United States on seat belt use — even though, in 2013, 87 percent of people in the United States reported wearing safety belts while riding in the front seat.
Spain saw the biggest drop — 75 percent — in its crash death rate. That country improved nearly all aspects of road safety, including decreasing alcohol-impaired driving and increasing seat belt use, the researchers say.
Thirst drove one of the last populations of woolly mammoths to extinction.
A small group of holdouts on an isolated Alaskan island managed to last about 8,000 years longer than most of their mainland-dwelling brethren. But by about 5,600 years ago, the island’s lakes — the only source of freshwater — became too small to support the mammoths (Mammuthus primigenius), scientists report online the week of August 1 in the Proceedings of the National Academy of Sciences. “I don’t think I’ve ever seen something so conclusive about an extinction before,” says Love Dalén, an evolutionary geneticist at the Swedish Museum of Natural History in Stockholm who was not involved in the research. The study highlights “how sensitive small populations are and how easily they can become extinct.”
Surprisingly recent woolly mammoth bones had previously been discovered in a cave on St. Paul Island, which became isolated from the mainland roughly 14,000 years ago. Since there’s no evidence that prehistoric humans lived on St. Paul, the find provided a chance to study extinction in the absence of human influence, says Russell Graham, a paleontologist at Penn State who led the study.
The scientists extracted a core of sediment from a lake bed near the cave to see how environmental conditions had changed over the last 11,000 years. The team found remnants of ancient plants, animals and fungi in the sediment — including traces of mammoth DNA in some layers. By analyzing and dating the different sediment layers, the team could infer when and how the mammoths went extinct.
“We initially thought that vegetation change and habitat would be the major driving factor,” Graham says. Instead, his team found a wealth of evidence — including an increase in salt-tolerant algae and crustaceans 6,000 years ago — suggesting freshwater shortages as the culprit. A warmer climate after the last Ice Age ended contributed to the St. Paul mammoths’ downfall. Sea level rise shrank the mammoths’ island habitat and cut into their freshwater supplies by raising the water table and making the lake saltier over time, the team concluded. Warmer, drier conditions also caused water to evaporate more quickly from the lake surface.
The study highlights an often-overlooked vulnerability of island and coastal communities. Some islands in the South Pacific are currently experiencing similar freshwater shortages thanks to rising seas, Graham says – and Florida could be next in line. That’s particularly bad news for large island-dwelling and coastal mammals, which tend to need more water to survive than smaller species.
In a few highly specialized laboratories, scientists bombard matter with the world’s most powerful electrical pulses or zap it with sophisticated lasers. Other labs squeeze heavy-duty diamonds together hard enough to crack them.
All this is in pursuit of a priceless metal. It’s not gold, silver or platinum. The scientists’ quarry is hydrogen in its most elusive of forms.
Several rival teams are striving to transform hydrogen, ordinarily a gas, into a metal. It’s a high-stakes, high-passion pursuit that sparks dreams of a coveted new material that could unlock enormous technological advances in electronics. “Everybody knows very well about the rewards you could get by doing this, so jealousy and envy [are] kind of high,” says Eugene Gregoryanz, a physicist at the University of Edinburgh who’s been hunting metallic hydrogen for more than a decade.
Metallic hydrogen in its solid form, scientists propose, could be a superconductor: a material that allows electrons to flow through it effortlessly, with no loss of energy. All known superconductors function only at extremely low temperatures, a major drawback. Theorists suspect that superconducting metallic hydrogen might work at room temperature. A room-temperature superconductor is one of the most eagerly sought goals in physics; it would offer enormous energy savings and vast improvements in the transmission and storage of energy.
Metallic hydrogen’s significance extends beyond earthly pursuits. The material could also help scientists understand our own solar system. At high temperatures, compressed hydrogen becomes a metallic liquid — a form that is thought to lurk beneath the clouds of monstrous gas planets, like Jupiter and Saturn. Sorting out the properties of hydrogen at extreme heat and high pressure could resolve certain persistent puzzles about the gas giants. Researchers have reported brief glimpses of the liquid metal form of hydrogen in the lab — although questions linger about the true nature of the material.
While no lab has yet produced solid metallic hydrogen, the combined efforts of many scientists are rapidly closing in on a more complete understanding of the element itself — as well as better insight into the complex inner workings of solids. Hydrogen, the first element in the periodic table and the most common element in the universe, ought to be easy to understand: a single proton paired with a single electron. “What could be more simple than an assembly of electrons and protons?” asks theoretical physicist Neil Ashcroft of Cornell University. But at high pressures, the physics of hydrogen rapidly becomes complex.
At room temperature and atmospheric pressure, hydrogen is a gas. But like other materials, altered conditions can transform hydrogen into a solid or a liquid. With low enough temperatures or a sufficiently forceful squeeze, hydrogen shape-shifts into a solid. Add heat while squeezing, and it becomes a liquid.
If subjected to still more extreme conditions, hydrogen can — at least theoretically — undergo another transformation, into a metal. All metals have one thing in common: They conduct electricity, due to free-flowing electrons that can go where they please within the material. Squeeze anything hard enough and it will become a metal. “Pressure does a great job of dislodging the outer electrons,” Ashcroft says. This is what scientists are aiming to do with hydrogen: create a sloshing soup of roving electrons in either a liquid or a solid.
When hydrogen is compressed, many atoms begin to interact with one another, while paired in molecules of two hydrogen atoms each. The underlying physics becomes a thorny jumble. “It is amazing; the stuff takes up incredibly complex arrangements in the solid state,” says Ashcroft, the first scientist to propose, in 1968, that metallic hydrogen could be a high-temperature superconductor.
Hydrogen’s complexity fascinates scientists. “It’s not just the metallization question that’s of interest to me,” says Russell Hemley, a chemist at the Carnegie Institution for Science in Washington, D.C., and Lawrence Livermore National Laboratory in California. Studying the intricacies of hydrogen’s behavior can help scientists refine their understanding of the physics of materials.
In 1935, when physicists Eugene Wigner and Hillard Bell Huntington of Princeton University first predicted that compressed solid hydrogen would be metallic, they thought the transition to a metal might occur at a pressure 250,000 times that of Earth’s atmosphere. That may sound like a lot, but scientists have since squeezed hydrogen to pressures more than 10 times as high — and still no solid metal.
Scientists originally expected that the transition would be a simple flip to metallic behavior. Not so, says theoretical physicist David Ceperley of the University of Illinois at Urbana-Champaign. “Nature has a lot more possibilities.” Solid hydrogen exists in multiple forms, each with a different crystal structure. As the pressure climbs, the wily hydrogen molecules shift into ever-more-complex arrangements, or phases. (For physicists, the “phase” of matter goes deeper than the simple states of solid, liquid or gas.) The number of known solid phases of hydrogen has grown steadily as higher pressures are reached, with four phases now well established. The next phase scientists find could be a metal — they hope.
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Timeline: The race to make metallic hydrogen Rival research teams are rushing to transform solid or liquid hydrogen into a metal. With each experiment, the pressure rises. They have two very different aims: a room-temperature superconductor and a window into the gas giants. If solid metallic hydrogen turns out to be a room-temperature superconductor, it would have to be crushed to work, making it impractical for many applications. But if hydrogen could hold its metallic form after the pressure is released, as some researchers have suggested, “it would be revolutionary,” says physicist Isaac Silvera, who leads the metallic hydrogen hunt at Harvard University. Such a material could be used in electrical wires to reduce loss of energy and decrease the world’s power consumption. And it might lead to efficient, magnetically levitated trains and technological advances in nuclear fusion, supercomputing and more.
While one group of would-be metallurgists is searching for solid metal, other investigators seek the scientifically intriguing liquid hydrogen metal. Their techniques differ in timescale and size. To produce liquid metal, scientists violently slam hydrogen for fractions of a second at a time, using enormous machines at national laboratories. Scientists searching for a solid metal, on the other hand, use fist-sized devices to capture hydrogen between the tips of two tiny diamonds and slowly squeeze.
Diamonds have it rough Crushing an ethereal, normally gaseous substance between two diamonds sounds nearly impossible. Such tricky experiments make for a field where researchers are in regular disagreement over their latest results. “We’re still missing high-quality, reliable data,” says physicist Alexander Goncharov. “The issue is the experiments are too challenging.”
In his office at the Geophysical Laboratory of the Carnegie Institution, Goncharov opens a desk drawer and pulls out a device called a diamond anvil cell. The cylinder of metal is small enough for Goncharov to cradle in his palm. Bits of precisely machined steel and tough tungsten carbide are held together with four screws. Through portals in the top and bottom, bright sparkles shimmer: diamonds.
Inside the capsule, two diamonds taper to tiny points a few hundredths of a millimeter wide. They pinch the material within, squashing it at over a million times atmospheric pressure. The gap between the minuscule anvils can be as small as a few thousandths of a millimeter, about the size of a human red blood cell.
Once they’ve been pressurized, diamond anvil cells will hold the pressure almost indefinitely. The prepared cells can be carried around — inspected in the laboratory, transported to specialized facilities around the world — or simply stored in a desk drawer. Goncharov regularly travels with them. (Tip from the itinerant scientist: If questions arise at airport security, “never use the word ‘diamonds.’ ”) The diamond anvil can squeeze more than hydrogen — materials from iron to sodium to argon can be crushed in the diamond vise. To identify new, potentially metallic phases of solid hydrogen within the pressurized capsules, scientists shine laser light onto the material, measuring how molecules vibrate and rotate — a technique called Raman spectroscopy (SN: 8/2/08, p. 22). If a new phase is reached, molecules shift configurations, altering how they jiggle. Certain types of changes in how the atoms wobble are a sign that the new phase is metallic. If the material conducts electricity, that’s another dead giveaway. A final telltale sign: The normally translucent hydrogen should acquire a shiny, reflective surface.
Significant hurdles exist for diamond anvil cell experiments. Diamonds, which cost upwards of $600 a pop, can crack under such intense pressures. Hydrogen can escape from the capsule, or diffuse into the diamonds, weakening them. So scientists coat their diamonds with thin layers of protective material. The teams each have their own unique recipe, Goncharov says. “Of course, everyone believes that their recipe is the best.”
Three phases of solid hydrogen have been known since the late 1980s. With the discovery of a fourth phase in 2011, “the excitement was enormous,” Gregoryanz says. In Nature Materials, Mikhail Eremets and Ivan Troyan at the Max Planck Institute for Chemistry in Mainz, Germany, reported that a new phase appeared when they squashed room-temperature hydrogen to over 2 million times atmospheric pressure. Goncharov, Gregoryanz and colleagues created the new phase and deduced its structure in Physical Review Letters in 2012. In phase IV, as it’s known, hydrogen arranges itself into thin sheets — somewhat like the single-atom-thick sheets of carbon known as graphene, the scientists wrote.
Progress doesn’t come easy. With each new paper, scientists disagree about what the results mean. When Eremets and colleagues discovered the fourth phase, they thought they also had found metallic hydrogen (SN: 12/17/11, p. 9). But that assertion was swiftly criticized, and it didn’t stand up to scrutiny.
The field has been plagued by hasty claims. “If you look at the literature for the last 30 years,” Gregoryanz says, “I think every five years there is a claim that we finally metallized hydrogen.” But the claims haven’t been borne out, leaving scientists perpetually skeptical of new results.
In a recent flurry of papers, scientists have proposed new phases — some that might be metallic or metal-like precursors to a true metal — and they are waiting to see which claims stick. Competing factions have volleyed papers back and forth, alternately disagreeing and agreeing.
A paper from Gregoryanz’s group, published in Nature in January, provided evidence for a phase that was enticingly close to a metal (SN Online: 1/6/16), at more than 3 million times atmospheric pressure. But other scientists disputed the evidence. In their own experiments, Eremets and colleagues failed to confirm the new phase. In a paper posted online at arXiv.org just days after Gregoryanz’s paper was published, Eremets’ team unveiled hints of a “likely metallic” phase, which occurred at a different temperature and pressure than Gregoryanz’s new phase.
A few months later, Silvera’s group squeezed hydrogen hard enough to make it nearly opaque, though not reflective — not quite a metal. “We think we’re just below the pressure that you need to make metallic hydrogen,” Silvera says. His findings are consistent with Eremets’ new phase, but Silvera disputes Eremets’ speculations of metallicity. “Every time they see something change they call it metallic,” Silvera says. “But they don’t really have evidence of metallic hydrogen.”
All this back and forth may seem chaotic, but it’s also a sign of a swiftly progressing field, the researchers say. “I think it’s very healthy competition,” Gregoryanz says. “When you realize that somebody is getting ahead of you, you work hard.”
The current results are “not very well consistent, so everybody can criticize each other,” Eremets says. “For me it’s very clear. We should do more experiments. That’s it.”
There are signs of progress. In 2015, Eremets and colleagues discovered a record-breaking superconductor: hydrogen sulfide, a compound of hydrogen and sulfur. When tightly compressed into solid form, hydrogen sulfide superconducts at temperatures higher than ever seen before: 203 kelvins (−70° Celsius) (SN: 8/8/15, p. 12).
Adding sulfur to the mix stabilizes and strengthens the hydrogen structure but doesn’t contribute much to its superconducting properties. Hydrogen sulfide is so similar to pure hydrogen, Eremets says, that, “in some respects we already found superconductivity in metallic hydrogen.”
Brief glimmers Giant, gassy planets are chock-full of hydrogen, and the element’s behavior under pressure could explain some of these planets’ characteristics. A sea of flowing liquid hydrogen metal may be the source of Jupiter’s magnetic field (SN: 6/25/16, p. 16). Learning more about metallic hydrogen’s behavior deep inside such planets could also help resolve a long-standing puzzle regarding Saturn: The ringed behemoth is unexpectedly bright. The physics of hydrogen’s interactions with helium inside the planet could provide the explanation.
Using a radically different set of technologies, a second band of scientists is on the hunt for such liquid metallic hydrogen. These researchers have gone big, harnessing the capabilities of new, powerful machines designed for nuclear fusion experiments at government-funded national labs. These experiments show the most convincing evidence of metallic behavior so far — but in hydrogen’s liquid, not solid, form. These enormous machines blast hydrogen for brief instants, temporarily sending pressures and temperatures skyrocketing. Such experiments reach searing temperatures, thousands of kelvins. With that kind of heat, metallic hydrogen appears at lower, more accessible pressures. Creating such conditions requires sophisticated equipment. The Z machine, located at Sandia National Laboratories in Albuquerque, generates extremely intense bursts of electrical power and strong magnetic fields; for a tiny instant, the machine can deliver about 80 terawatts (one terawatt is about the total electrical power–generating capacity in the entire United States).
A group of scientists recently used the Z machine to launch a metal plate into a sample of deuterium — an isotope of hydrogen with one proton and one neutron in its nucleus — generating high pressures that compressed the material. The pummeled deuterium showed reflective glimmers of shiny metal, the scientists reported last year in Science. “It starts out transparent, it goes opaque, and then later we see this reflectivity increase,” says Marcus Knudson of Sandia and Washington State University in Pullman.
Another group is pursuing a different tactic, using some of the most advanced lasers in the world, at the National Ignition Facility at Lawrence Livermore. Scientists there zap hydrogen to produce high pressures and temperatures. Though the conclusions of this experiment are not yet published, says physicist Gilbert Collins of Lawrence Livermore, one of the leaders of the experiment, “we have some really beautiful results.”
The first experiment to show evidence of liquid metallic hydrogen was performed at Lawrence Livermore in the 1990s. A team of physicists including William Nellis, now at Harvard, used a sophisticated gunlike apparatus to shoot projectiles into hydrogen at blisteringly fast speeds. The resulting hydrogen briefly conducted electricity (SN: 4/20/96, p. 250).
These experiments face hurdles of their own — it’s a struggle to measure temperature in such systems, so scientists calculate it rather than measuring it directly. But many researchers are still convinced by these results. Metallic hydrogen “certainly has been produced by shock techniques,” Cornell’s Ashcroft says.
Some scientists still have questions. “It’s certainly difficult to tell if something is a metal or not at such high temperature,” Collins says. Although they need high temperatures to reach the metal liquid phase, some physicists define a metal based on its behavior at a temperature of absolute zero. Current experiments hit high pressures at temperatures as close to zero as possible to produce relatively cool liquid metallic hydrogen.
Scientists who conduct palm-sized diamond anvil cell experiments refuse to be left out of the liquid-metal action. They’ve begun to use laser pulses to heat and melt hydrogen crammed into the cells. The results have stirred up new disagreements among competing groups. In April’s Physical Review B, Silvera and coauthors reported forming liquid metallic hydrogen. But under similar conditions, Goncharov and others found only semiconducting hydrogen, not a metal. They reported their results in Physical Review Letters in June.
“There’s kind of a crisis now with these different experiments,” says Illinois theorist Ceperley. “And there’s a lot of activity trying to see who’s right.” For now, scientists will continue refining their techniques until they can reach agreement.
The major players have managed to reach consensus before. Four phases of solid hydrogen are now well established, and researchers agree on certain conditions under which solid hydrogen melts.
Solid metallic hydrogen, however, has perpetually seemed just out of reach, as theoretical predictions of the pressure required to produce it have gradually shifted upward. As the goalposts have moved, physicists have reached further, achieving ever-higher pressures. Current theoretical predictions put the metal tantalizingly close — perhaps only an additional half a million times atmospheric pressure away.
The quest continues, propelled by a handful of hydrogen-obsessed scientists.
“We all love hydrogen,” Collins says. “It has the essence of being simple, so that we think we can calculate something and understand it, while at the same time it has such a devious nature that it’s perhaps the least understandable material there is.”
As our first beach vacation with two little kids loomed, I had to do one of those chores that sounds easy but turns out to be anything but. I had to buy sunscreen. It seems like the task should take five minutes on Amazon. But as any parent with an internet connection knows, the choice is fraught.
You can pick from formulas that block rays with chemicals or minerals such as zinc oxide. SPFs can surpass 100. There are lotions and sprays, “organic” and “natural,” “sensitive” and “sport.” Some are marketed specifically for kids. Some are endorsed by various interest groups. And then there’s the cost. Highly rated sunscreens on Amazon vary in cost by 3,000 percent. Amid the chaos, I ended up picking an SPF 30 and being done with it.
With the beach vacation behind us, I’ve had the presence of mind to take a clear-eyed look at the sunscreen boondoggle. It seems that my trouble was in some ways a mess of my own making. I was distracted by zippy marketing words that obscured the core attributes of a good sunscreen. It turns out that the task can be pretty simple, if you keep a few key things in mind.
Look for SPF of 30 or higher. The sun protection factor is a measurement that tells you how long the sunscreen will protect your skin from sunburn-causing ultraviolet-B rays, as compared to no sunscreen at all. Sunscreens with an SPF of 30 will protect you from UV-B rays for 30 times longer than normal. Say you’d normally burn after 20 minutes in the sun without any sunscreen. After you correctly apply a sunscreen with SPF 30, you’d be able to go 10 hours. Sunscreens with an SPF of 30 will block 97 percent of UV-B rays. There may be diminishing returns as the SPF number goes up, though. There’s little evidence that SPFs over 50 offer increasing protection.
Make sure the sunscreen says “broad spectrum” on the label. That means the sunscreen will thwart both UV-A and UV-B rays. UV-A rays are thought to be responsible for deep skin damage, while UV-Bs are the ones that cause sunburns. Both flavors of the sun’s rays can increase the risk of skin cancer.
Choose one that’s water resistant. That doesn’t mean that water won’t wash it off. No sunscreen is completely waterproof, a fact that means sunscreens are no longer allowed to make that claim.
Don’t necessarily trust the ratings. Of the sunscreens in the top 1 percent on Amazon, a full 40 percent of them failed to meet the criteria set out by the American Academy of Dermatology — SPF of 30 or higher, broad spectrum and water resistant, a recent JAMA Dermatology paper found.
Use it. As study coauthor Steve Xu of Northwestern University says, “Picking the right product is only the first step. Using it correctly is just as important.” Put sunscreen on to your kids before they go outside, so the sunscreen can soak in. Make sure to cover all exposed skin, including the tops of ears and toes. And reapply every two hours, or immediately after your kids get out of water.
Those are the main points. Of course, you could choose to wade through a lot more weeds in the decision. Sunscreens based on physical blockers, such as zinc oxide or titanium dioxide, reflect the sun’s rays. Chemical blockers such as oxybenzone absorb the rays and get rid of the extra energy in harmless ways. Mineral-based sunscreens may be less likely to irritate babies’ and children’s skin than chemical blockers, for instance.
The jury is still out on spray sunscreen, which aerosolizes the particles and promises fewer child chase-downs. The FDA has called for more data to evaluate those. And then there’s the question of sunscreen for babies younger than six months. Most sources say that when possible, opt for shade and hats instead of sunscreen for the littlest babies.
So as you prepare for your time in the sun, stick to a few basic facts to help you choose a sunscreen. Instead, apply the time you save toward forcing cute sunhats on your squirmy kids.
Fractions of a second after food hits the mouth, a specialized group of energizing nerve cells in mice shuts down. After the eating stops, the nerve cells spring back into action, scientists report August 18 in Current Biology. This quick response to eating offers researchers new clues about how the brain drives appetite and may also provide insight into narcolepsy.
These nerve cells have intrigued scientists for years. They produce a molecule called orexin (also known as hypocretin), thought to have a role in appetite. But their bigger claim to fame came when scientists found that these cells were largely missing from the brains of people with narcolepsy. People with narcolepsy are more likely to be overweight than other people, and this new study may help explain why, says neuroscientist Jerome Siegel of UCLA. These cells may have more subtle roles in regulating food intake in people without narcolepsy, he adds.
Results from earlier studies hinted that orexin-producing nerve cells are appetite stimulators. But the new results suggest the opposite. These cells actually work to keep extra weight off. “Orexin cells are a natural obesity defense mechanism,” says study coauthor Denis Burdakov of the Francis Crick Institute in London. “If they are lost, animals and humans gain weight.”
Mice were allowed to eat normally while researchers eavesdropped on the behavior of their orexin nerve cells. Within milliseconds of eating, orexin nerve cells shut down and stopped sending signals. This cellular quieting was consistent across foods. Peanut butter, mouse chow, a strawberry milkshake and a calorie-free drink all prompted the same response. “Foods with different flavors and textures had a similar effect, implying that it is to do with the act of eating or drinking, rather than with what is being eaten,” Burdakov says. When the eating ended, the cells once again resumed their activity. When Burdakov and colleagues used a genetic technique to kill orexin nerve cells, mice ate more food than normal, behavior that led to weight gain, the team found. But a reduced-calorie diet slimmed these mice down. The results suggest that giving orexin to people who lack it may reduce obesity. But that might not be a good idea. An overactive orexin system has been tied to stress and anxiety, Burdakov says. Orexin’s link to stress raises a different possibility —that anxiety can be reduced by curbing orexin nerve cell activity. “And our study suggests that the act of eating can do just that,” Burdakov says. “This provides a candidate explanation for why people turn to eating at times of anxiety.”
Thirsty zebra finches “drink” their body fat. The songbirds are the first birds shown to get through a day without water by breaking down adipose tissue to stay hydrated, says evolutionary physiologist Ulf Bauchinger.
Two earlier tests of deprived birds summoning water from their tissues report that birds rely on protein. But zebra finches (Taeniopygia guttata) coped with one-day droughts in the lab not by breaking down such tissues as muscle but with the safer choice of metabolizing fat, say Bauchinger, Joanna Rutkowska and their colleagues at Jagiellonian University in Kraków, Poland. In comfortable temperatures and humidity, the little birds (averaging 13.5 grams in weight) produced about 0.444 grams of water metabolically. That boost would have taken large amounts of fleshy moist protein, equivalent to one-third the mass of their flight muscles or three times the mass of their hearts, the researchers say online August 31 in the Journal of Experimental Biology. “Exciting,” says Alexander Gerson of the University of Massachusetts Amherst, whose own work has shown birds taking the protein route. Gerson’s interest in animals deriving water by metabolizing body parts traces to research on migratory birds surviving several thousand kilometers of flight across the Sahara. His wind-tunnel tests of five-hour flights in dry air suggested that birds were fueling their flight with energy from fat reserves but were supplementing with water produced by breaking down protein.
What deprived birds do when they’re not migrating, however, might involve different trade-offs. But Gerson’s work with house sparrows kept from water still showed evidence of metabolizing proteins.
Unlike house sparrows, zebra finches have an evolutionary history of life in dry places, such as arid Australia. To see their water-management techniques, the researchers in Poland created total food and/or water shortages for lab birds just doing mundane finch things in cages instead of crossing a desert.
All the birds reached the end of their bad day without signs of dehydration, the researchers found. But 12 birds deprived of food and water showed more total fat loss than another 12 birds allowed to drink but not eat. Parched finches had 42 percent less fat than birds that had access to drinking water. Measures of lost lean tissue, including protein-rich muscle, barely differed.
Other bird species might respond to water shortages in the same way, Rutkowska speculates. Her test method differs a bit from the sparrow work. Gerson muses that zebra finches, with arid lands in their native range, might have different thresholds for metabolizing fat versus protein than house sparrows do.
For humans, Rutkowska says she gets asked about implications for dieting. Her answer: Sorry, no evidence of miracle shortcuts here.
Few people today could recite the scientific accomplishments of 19th century physician Julius Petri. But almost everybody has heard of his dish.
For more than a century, microbiologists have studied bacteria by isolating, growing and observing them in a petri dish. That palm-sized plate has revealed the microbial universe — but only a fraction, the easy stuff, the scientific equivalent of looking for keys under the lamppost.
But in the light — that is, the greenhouse-like conditions of a laboratory — most bacteria won’t grow. By one estimate, a staggering 99 percent of all microbial species on Earth have yet to be discovered, remaining in the shadows. They’re known as “microbial dark matter,” a reference to astronomers’ description of the vast invisible matter in space that makes up most of the mass in the cosmos. In the last decade or so, though, scientists have developed new tools for growing bacteria and collecting genetic data, allowing faster and better identifications of microbes without ever removing them from natural conditions. A device called the iChip, for instance, encourages bacteria to grow in their home turf. (That device led to the discovery of a potential new antibiotic, in a time when infections are fast outwitting all the old drugs.) Recent genetic explorations of land, water and the human body have raised the prospect of finding hundreds of thousands of new bacterial species.
Already, the detection of these newfound organisms is challenging what scientists thought they knew about the chemical processes of biology, the tree of life and the manner in which microbes live and grow. The secrets of microbial dark matter may redefine how life evolved and exists, and even improve the understanding of, and treatments, for many diseases.
“Everything is changing,” says Kelly Wrighton, a microbiologist at Ohio State University in Columbus. “The whole field is full of enthusiasm and discovery.” Counter culture Microbiologists have in the past discovered new organisms without petri dishes, but those experiments were slow going. In one of her first projects, Tanja Woyke analyzed the bacterial community huddled inside a worm that lives in the Mediterranean Sea. Woyke, a microbiologist at the U.S. Department of Energy’s Joint Genome Institute in Walnut Creek, Calif., and colleagues published the report in Nature in 2006. It was two years in the making.
They relied on metagenomics, which involves gathering a sample of DNA from the environment — in soil, water or, in this case, worm insides. After extracting the genetic material of every microbe the worm contained, Woyke and colleagues determined the order, or sequences, of all the DNA units, or bases. Analyzing that sequence data allowed the researchers to infer the existence of four previously unknown microbes. It was a bit like obtaining boxes of jigsaw puzzle pieces that need assembly without knowing what the pictures look like or how many different puzzles they belong to, she says. The project involved 300 million bases and cost more than $100,000, using the time-consuming methods available at the time. Just as Woyke was wrapping up the worm endeavor, new technology came online that gave genetic analysis a turbo boost. Sequencing a genome — the entirety of an organism’s DNA — became faster and cheaper than most scientists ever predicted. With next-generation sequencing, Woyke can analyze more than 100 billion bases in the time it takes to turn around an Amazon order, she says, and for just a few thousand dollars. By scooping up random environmental samples and searching for DNA with next-generation sequencing, scientists have turned up entirely new phyla of bacteria in practically every place they look. In 2013 in Nature, Woyke and her colleagues described more than 200 members of almost 30 previously unknown phyla. Finding so many phyla, the first big groupings within a kingdom, tells biologists that there’s a mind-boggling amount of uncharted diversity.
Woyke has shifted from these broad genetic fishing expeditions to working on individual bacterial cells. Gently breaking them open, she catalogs the DNA inside. Many of the organisms she has found defy previous rules of biological chemistry. Two genomes taken from a hydrothermal vent in the Pacific Ocean, for example, contained the code UGA, which stands for the bases uracil, guanine and adenine in a strand of RNA. UGA normally separates the genes that code for different proteins, acting like a period at the end of a sentence. In most other known species of animal or microbe, UGA means “stop.” But in these organisms, and one found about the same time in a human mouth, instead of “stop,” the sequence codes for the amino acid glycine. “That was something we had never seen before,” Woyke says. “The genetic code is not as rigid as we thought.”
Other recent finds also defy long-held notions of how life works. This year in the ISME Journal, Ohio State’s Wrighton reported a study of the enzyme RubisCO taken from a new microbial species that had never been grown in a laboratory. RubisCO, considered the most abundant protein on Earth, is key to photosynthesis; it helps convert carbon from the atmosphere into a form useful to living things. Because the majority of life on the planet would not exist without it, RubisCO is a familiar molecule — so familiar that most scientists thought they had found all the forms it could take. Yet, Wrighton says, “we found so many new versions of this protein that were entirely different from anything we had seen before.”
The list of oddities goes on. Some newly discovered organisms are so small that they barely qualify as bacteria at all. Jillian Banfield, a microbiologist at the University of California, Berkeley, has long studied the microorganisms in the groundwater pumped out of an aquifer in Rifle, Colo. To filter this water, she and her colleagues used a mesh with openings 0.2 micrometers wide — tiny enough that the water coming out the other side is considered bacteria-free. Out of curiosity, Banfield’s team decided to use next-generation sequencing to identify cells that might have slipped through. Sure enough, the water contained extremely minuscule sets of genes. “We realized these genomes were really, really tiny,” Banfield says. “So we speculated if something has a tiny genome, the cells are probably pretty tiny, too.” And she has pictures to prove it. Last year in Nature Communications, she and her team published the first images (taken with an electron microscope) and detailed description of these ultrasmall microbes (see, right). They are probably difficult to isolate in a petri dish, Banfield says, because they are slow-growing and must scavenge many of the essential nutrients they need from the environment around them. Part of the price of a minigenome is that you don’t have room for the DNA to make everything you need to live.
Relationship status: It’s complicated Banfield predicts that an “unimaginably large number” of species await in every cranny of the globe — soil, rocks, air, water, plants and animals. The human microbiome alone is probably teeming with unfamiliar microbial swarms. As a collection of organisms that live on and in the body, the human microbiome affects health in ways that science is just beginning to comprehend (SN: 2/6/16, p. 6).
Scientists from UCLA, the University of Washington in Seattle and colleagues recently offered the most detailed descriptions yet of a human mouth bacterium belonging to a new phylum: TM7. (TM stands for “Torf, mittlere Schicht,” German for a middle layer of peat; organisms in this phylum were first detected in the mid-1990s in a bog in northern Germany.) German scientists found TM7 by sifting through soil samples, using a test that’s specific for the genetic information in bacteria. In the last decade, TM7 species have been found throughout the human body. An overabundance of TM7 appears to be correlated with inflammatory bowel disease and gum disease, plus other conditions.
Until recently, members of TM7 have stubbornly resisted scientists’ efforts to study them. In 2015, Jeff McLean, a microbiologist at the University of Washington, and his collaborators finally isolated a TM7 species in a lab and deciphered its full genome. To do so, the team combined the best of old and new technology: First the researchers figured out how to grow most known oral bacteria together, and then they gradually thinned down the population until only two species remained: TM7 and a larger organism.
“The really remarkable thing is we finally found out how it lives,” McLean says, and why it wouldn’t grow in the lab. They discovered that this species of TM7, like the miniature bacteria in Colorado groundwater, doesn’t have the cellular machinery to get by on its own. Even more unusual, these bacteria pilfer missing amino acids and whatever else they need by latching on, like parasites, to a larger bacterium. Eventually they can kill their host. “We think this is the first example of a bacterium that lives in this manner,” McLean says.
He expects to see more unusual relationships among microbes as the dark matter comes to light. Many have evaded detection, he suspects, because of their small size (sometimes perhaps mistaken for bacterial debris) and dependence on other organisms for survival. In 2013 in the Proceedings of the National Academy of Sciences, McLean and colleagues were the first to describe a member of another uncultivated phylum, TM6. They found this group growing in the slime in a hospital sink drain. Later studies determined that the organism lives by tucking itself inside an amoeba. One of the greatest hopes for microbial dark matter exploration is that newly found microbes might provide desperately needed antibiotics. From the 1940s to the 1960s, scientists discovered 10 new classes of drugs by testing chemicals found in soil and elsewhere for action against common infections. But only two classes of medically important antibiotics have been discovered in the last 30 years, and none since 1997. Some major infections are at the brink of being unstoppable because they’ve become resistant to most existing drugs (SN Online: 5/27/16). Many experts think that natural sources of antibiotics have been exhausted.
Maybe not. In 2015, a research team led by scientists from Northeastern University in Boston captured headlines after describing in Nature a new chemical extracted from a ground-dwelling bacterium in Maine. The scientists isolated the organism using the iChip, a thumb-sized tool that contains almost 400 separate wells, each large enough to hold only an individual bacterial cell plus a smidgen of its home dirt. The bacteria grow on this scaffold in part because they never leave their natural surroundings. In lauding the discovery, Francis Collins, director of the National Institutes of Health, called the iChip “an ingenious approach that enhances our ability to search one of nature’s richest sources of potential antibiotics: soil.” So far, the research team has discovered about 50,000 new strains of bacteria.
One strain held an antibiotic, named teixobactin (SN: 2/7/15, p. 10). In laboratory experiments, it killed two major pathogens in a way that did not appear easily vulnerable to the development of resistance. Most antibiotics work by disrupting a microbe’s survival mechanism. Over time, the bacteria genetically adapt, find a work-around and overcome the threat. This new antibiotic, however, prevents a microbe from assembling the molecules it needs to form an outer wall. Since the antibiotic interrupts a mechanical process and not just a specific chemical reaction, “there’s no obvious molecular target” for resistance, says Kim Lewis, a microbiologist at Northeastern. Everything is illuminated Some microbiologists feel like astronomers who, after years of staring up into the dark, were just handed the Hubble Space Telescope. Billions of galaxies are coming into view. Banfield expects this new microbial universe to be mapped over the next few years. Then, she says, an even more exciting era begins, as science explores how these dark matter bacteria make a living. “They are doing a lot of things, and we have no idea what,” she says.
Part of the excitement comes from knowing that microbes have a history of granting unexpected solutions to problems that scientists never expected to solve. Consider that the enzyme that makes the laboratory technique PCR possible came from organisms that live inside the thermal vents at Yellowstone National Park. PCR, which works like a photocopier to make multiple copies of DNA segments, is now used across a range of situations, from diagnosing cancer to paternity testing. CRISPR, a powerful gene-editing technology, relies on “molecular scissors” that were found in bacteria (SN: 9/3/16, p. 22).
Banfield estimates that 30 to 50 percent of newly discovered organisms contain proteins that never met a petri dish. Their function in the chemistry of life is an obscure mystery. Since microbes are the world’s most abundant organism, Banfield says, “the vast majority of life consists of biochemistry we don’t understand.” But once we do, the future could be very bright.
In a recent poll, more than four-fifths of U.S. adults could not name a living scientist. Of those who could, the plurality (40 percent) named Stephen Hawking. (The next highest response was Neil deGrasse Tyson, followed by Jane Goodall.) No offense to the rightfully famous Hawking, but at Science News we would like to change these results. Why aren’t more scientists, particularly those who are young and accomplished, household names? Where, we want to know, are the Taylor Swifts of science?
You’ll find some of them below. For the second year in a row, Science News is highlighting 10 early- and mid-career scientists on their way to widespread acclaim. The SN 10: Scientists to Watch includes a laser physicist with laserlike focus, a materials scientist challenging what it means to be alive and a computational biologist willing to get personal with his microbiome, among many others who are making important advances in their chosen fields.
Though none of these scientists have recorded hit singles — at least not that our reporting uncovered — all were nominated by a Nobel laureate or recently elected member of the National Academy of Sciences. And all were age 40 or younger at the time of nomination.
These remarkable individuals have diverse personalities and talents: They are tenacious and creative, practical-minded and dreamers. They are lab animals and data heads. Some seek simplicity, others complexity. If there is one unifying trait, though, it would have to be their passion — a quality so cliché among successful scientists that it has to be true. As Marie Curie famously wrote in a letter to her sister, “Sometimes my courage fails me and I think I ought to stop working…. But I am held by a thousand bonds.” She did not know, she confessed, whether she could live without the laboratory.
After a year caring for patients at the heart of Brazil’s Zika epidemic, pediatric neurologist Vanessa van der Linden has seen some of the worst cases.
She was one of the first researchers to link Zika virus to microcephaly, a now well-known birth defect marked by a small, misshapen head and, sometimes, a forehead that slopes backward. Babies with the defect can have other symptoms, too: Van der Linden has seen 24-hour crying bouts, spasms, extreme irritability and difficulty swallowing. But microcephaly is just the tip of the Zika iceberg, she said September 22 at a workshop hosted by the National Institutes of Health in North Bethesda, Md. That’s something public health officials have been warning about for months. Now, scientists have begun to describe a head-to-toe assortment of health problems linked to Zika virus infection in utero; they’re calling it congenital Zika syndrome.
Still, the full scope of the problem, including the threat of more subtle neurologic disorders such as learning disabilities or developmental delays, remains murky, says Peter Hotez, a pediatrician and microbiologist at Baylor College of Medicine in Houston.
“That’s the big unknown: There’s probably a spectrum of illness,” similar to autism, he says. And it could take years for scientists to sort it all out.
It’s a problem that Brazil is facing now, and one that Puerto Rico has just begun grappling with.
As of September 23, the U.S. territory had reported 22,358 confirmed cases of Zika infection. Of these cases, 1,871 are pregnant women. Carmen Zorrilla, an obstetrician-gynecologist at the University of Puerto Rico’s Maternal-Infant Studies Center who has examined some of these women and their babies, emphasizes the importance of following up on all babies exposed to Zika in the womb — even those without apparent birth defects. “Even if they are born normal,” she said, “it doesn’t mean they’ll be OK.”
Insidious problems At the workshop, Zorrilla described the case of one of the first Puerto Rican babies born to a mother diagnosed with Zika. The baby didn’t have microcephaly, but she did have another unusual problem: She couldn’t open her eyes. A bad case of conjunctivitis (pinkeye) left her needing help opening her eyelids every morning — even 27 days after birth. Zorrilla can’t say for sure whether the problem was related to Zika, but “it really concerned me,” she said. “This is the first baby I’ve seen with conjunctivitis that lasted for so long.”
The case may be another clue that Zika’s assaults on the body are widespread. And Zorrilla can expect to see more cases soon. Ultrasound examinations of 228 women in Puerto Rico with confirmed Zika infection have spotted brain abnormalities in 13 fetuses, including one with microcephaly.
Another observation could hint at problems yet to come: Most of the Zika-exposed fetuses tended to have slightly smaller heads than average, although “still within the normal limits,” Zorrilla said. But measurements of leg bones and stomach size indicate that the rest of the body is growing normally. Implications remain unclear, but the findings — preliminary results from Alberto de la Vega, also an obstetrician-gynecologist at the University of Puerto Rico — are the latest in a litany of anomalies linked to Zika.
Long-term problems aren’t unusual in babies infected with a different kind of virus that causes microcephaly. Like Zika, cytomegalovirus can infect babies in the womb. Most CMV-infected babies don’t have any obvious symptoms, but asymptomatic kids may have problems as they grow, including intellectual disabilities, hearing loss or cerebral palsy, researchers suggested in the October Brain and Development.
Beyond microcephaly, scientists have recently described other symptoms linked to Zika infection. In some babies, for example, Zika seems to damage hearing. Of 70 Zika-exposed infants born with microcephaly, 10 percent had some hearing loss, researchers noted in a Sept. 2 report published by the U.S. Centers for Disease Control and Prevention. Zika can leave a mark on the eyes, too. More than a third of 29 babies with microcephaly had some sort of eye oddity, including mottled pigmenting and withered tissue, researchers reported in May in JAMA Ophthalmology.
Van der Linden has also observed a link between Zika and a deformity called arthrogryposis, where a child’s joints can be stuck in contorted positions — even in babies without microcephaly. The condition might stem from problems with infected babies’ motor neurons, the nerve cells that relay messages from the brain to the muscles, van der Linden and colleagues suggested August 9 in BMJ.
She has even seen babies born with normal head circumferences who later develop microcephaly or other brain defects. One mother, she says, came in five months after giving birth because she thought her baby wasn’t developing normally. Like children with congenital Zika syndrome, the baby’s head scans revealed “the same pattern of brain damage,” van der Linden says. This pattern includes a malformed cerebral cortex, the wrinkled outer layer of the brain, and calcifications, strange lumps of calcium deposited within the tissue.
Infiltrating the brain Scientists still don’t know exactly how Zika damages the brain, but they have some ideas.
One recent report found that the virus can infiltrate and kill both neuroepithelial stem cells, which give rise to all sorts of brain cells, and radial glial cells, which can generate newborn neurons and help guide them to their proper place in the brain.
Zika also hinders these cells’ ability to split into new cells, Yale University neuroscientist Marco Onorati and colleagues reported September 6 in Cell Reports. Stem cells at work in the fetal brain eventually give rise to structures responsible for thought and memory and learning, raising concerns of a cascade of problems down the road. “This is a virus that blocks the development of the fetal brain,” Hotez says. “That’s about the worst thing you can possibly imagine.”
And fetuses might not be the only ones at risk, he points out. “Kids in the first years of life also have growing, developing brains,” he says. “What if they get infected with Zika?”
It’s not an easy question to answer. But another disease could offer clues.
Malaria, for example, can cause severe neurological problems. In children, a condition called cerebral malaria may be linked to mental health disorders such as attention-deficit/hyperactivity disorder, antisocial behavior and depression, researchers reported in March in Malaria Journal.
Researchers will also need to watch out for long-term troubles in Zika-exposed babies born with no obvious symptoms, says the CDC’s Sonja Rasmussen. “We don’t want to make families too scared,” she says. “But we do recognize the possibility of later-on seizures or developmental delay.”
Since most people don’t show signs of Zika infection, pinpointing the total number of pregnant women (and babies) exposed to the virus may be impossible.
In the Americas, at least, the number is probably enormous. Tens of thousands of children may eventually suffer some sort of neurologic or psychiatric illness triggered by Zika, Hotez predicted in a paper published in JAMA Pediatrics in August.
Van der Linden can’t say whether the babies she has seen have learning disabilities or psychiatric illnesses, or other more subtle cognitive problems — most of her patients are between 9 months and 1 year old.
But she plans to follow these patients, and the babies who appeared normal at birth, for years. “We need time to better understand the disease,” she says.
Hotez agrees: “It’s going to take a generation of pediatric neurologists and infectious disease experts to figure this out.”
