After several decades, researchers are finally getting a grasp on when an odd and destructive type of oxygen arises in chemical reactions in living cells and certain batteries.

Not all oxygen molecules are created equal. In some, their two most energetic electrons have opposite values of quantum spin while in others their spins match. When they are opposites, the molecule is known as “singlet oxygen”, which is highly reactive so it can cause toxic changes in proteins and fats within cells and eat away parts of some batteries. Since the 1960s, chemists have been working to determine when exactly this evil twin of the oxygen that we happily breathe arises in chemical reactions. at the Institute of Science and Technology Austria and his colleagues have now figured it out.

They carried out a series of experiments that started with a molecule of superoxide – a compound that contains oxygen and participates in chemical reactions used by mitochondria to power cells – and ended with the production of oxygen in either form. While cells have enzymes that help this process, the team tried different “mediator” molecules. This allowed them to record oxygen-making reactions with a broad range of driving forces, or energy differences that force the reaction to happen in the first place. They discovered that it is exactly this driving force that matters – for singlet oxygen to form, this force had to get very high.

“There was really truly a fierce debate about whether or not it [singlet oxygen] forms in the environment of cells. Up to now it has never been clarified,” says Freunberger.

Because mitochondria have high pH values that keep the driving force low, the new work implies that singlet oxygen is not produced in high quantities within these cellular powerhouses, which protects the cell from damage.

at ETH Zürich in Switzerland says that the question of singlet oxygen production has consequences beyond biology. “Wherever it’s generated it can damage or react with things that are in the neighbourhood,” he says. The analysis in the new study pertains to certain kinds of batteries and could be part of an explanation for why they sometimes corrode from the inside, says McNeill.

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Piping an oxygen-rich liquid through the anus could be a life-saver. A new treatment for failing lungs that involves such a process has been successfully tested in pigs.

People with low blood oxygen levels may be treated in intensive care by being put on a ventilator, which blows air into their lungs. But this usually requires sedation and can injure delicate lung tissue. “It can be really damaging,” says at the Tokyo Medical and Dental University.

Takebe wondered if people could absorb oxygen through their intestines, which happens in some freshwater fish. In mammals, the rectum is lined with a thin membrane that allows absorption of certain compounds into the bloodstream, and doctors already exploit this by giving some medicines as suppositories.

Takebe’s team tested the idea on pigs by giving them enemas of a type of fluid called a perfluorocarbon, which can hold high levels of oxygen. Such fluids have been investigated as a way of breathing liquid, and are already used to help protect the lungs of premature babies, so are likely to be non-toxic when used in this novel way, says Takebe.

The researchers anaesthetised four pigs and put them on a ventilator that gave them a lower breathing rate than normal, so their blood oxygen levels fell. When they gave two of the pigs enemas of the oxygenated fluid, replaced once an hour, their blood oxygen levels rose significantly after each infusion. The same effect happened when the fluid was delivered by a tube surgically inserted into the rectums of the other two pigs.

If there is a similar-sized effect in people, it would be enough to provide a medical benefit, says Takebe. He thinks the approach could be especially useful in low-income countries that have fewer intensive care facilities. “Ventilators are super-expensive and need a number of medical staff to manage,” he says. “This is just a simple enema.”

One problem is that gut function may be impaired in people sick enough to need intensive care, which can cause diarrhoea, says at Imperial College London. “It’s too early to say if this has got any legs,” he says.

“This is a provocative idea and those first encountering it will express astonishment,” wrote�� at Yale School of Medicine in an article accompanying the paper. But the idea of faecal transplants for people with recurrent intestinal infections also met initial resistance for “aesthetic reasons” yet is now accepted, he added.

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It may have been unexpectedly easy for the air to become rich in oxygen. A new simulation of the rise of oxygen suggests that it was driven by the planet itself, and needed little help from living organisms.

The finding implies that planets with oxygen-rich atmospheres could be more common than we thought. “It’s easier, not just for our planet, but possibly for others as well,” says Lewis Alcott at the University of Leeds, UK, one of the authors of the work.

For the first two billion years of Earth’s history, there was no oxygen in the air. That changed with the Great Oxidation Event around 2.4 billion years ago, when low levels of oxygen first appeared. This has often been attributed to the evolution of photosynthetic bacteria that release oxygen as a waste product.

: once between 800 and 540 million years ago, and again 450-400 million years ago.

We have previously tried to explain the oxidation events by linking them to major evolutionary shifts or tectonic activity, says co-author Simon Poulton, also at the University of Leeds. For instance, the final rise has been linked to the spread of land plants.

However, Alcott, Poulton and their colleague Benjamin Mills say there is no need to invoke any such dramatic events, other than the initial evolution of photosynthetic bacteria. They have shown that the behaviour of the planet is enough to explain the stepwise rises in oxygen levels.

The key is that Earth’s mantle has been gradually cooling since the planet formed, and as it cools, it releases fewer volcanic gases such as carbon monoxide, which react with oxygen and remove it from the air. When the team modelled how this shift affected the cycling of oxygen around the planet, they observed three sharp increases in oxygen that corresponded to the known oxidation events.

The initial Great Oxidation Event came about because the oxygen from bacteria overwhelmed the volcanic gases in the air. Levels then held steady for millions of years, because any extra oxygen reacted with minerals on land.

In the model, the second rise happened because the extra oxygen changed the nature of phosphorus-containing materials, making them more likely to be buried in sediments. Phosphorus is a vital nutrient, so this change meant fewer organisms that would otherwise have taken in oxygen could survive, allowing more oxygen to escape into the air and into surface layers of the sea. The same process led to a third sharp rise in oxygen, when it reached the deep ocean.

The same processes would play out on any planet that has oceans and continents, and where oxygen-releasing photosynthesis has evolved, says Poulton.

You may be able to thank the Milky Way’s spiral arms for supplying Earth with a fair share of the vital element at our planet’s birth.

Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium. It arises mainly in massive stars, which forge the element during their brief lives and then cast it into space when they explode.

But a galaxy’s spiral arms also help spread the wealth, says����at the Max Planck Institute for Astronomy in Heidelberg, Germany.

He and his colleagues have measured oxygen levels throughout a galaxy named NGC 1365 located 60 million light years away in the constellation Fornax. It has two gargantuan spiral arms joined together by a bar of older stars, all embedded in a huge disc of stars and interstellar gas and dust. As viewed from Earth, the galaxy rotates clockwise, but most of the stars and gas revolve faster than the spiral arms themselves.

Ho’s team has discovered that oxygen is 60 per cent more abundant in the spiral arms than in gas that has just passed through them.

��“To the best of our knowledge, this is the most extreme case so far,” Ho says.��In contrast, using older instruments, astronomers have failed to detect any variations in oxygen levels as one proceeds clockwise around most spiral galaxies.

We can’t see our galaxy from the outside, so it’s harder to do this in the Milky Way. Nevertheless, there are hints of such variation in our galaxy too.

In a spin

“It’s certainly a fascinating observation,” says at IBM Research in Yorktown Heights, New York.�� “It would not have been predicted, I think, and that’s why it’s so interesting.”�� Understanding the result, he says, will require simulations that incorporate spiral arms, star formation, supernova explosions and oxygen enrichment.

Ho thinks that as gas that has just passed through a spiral arm revolves toward the next arm, massive stars within the gas explode, raising the oxygen level. The next generation of newborn stars inherit this oxygen and raise the level further when they explode.��The abundance rises until the gas levels reach a peak in the next spiral arm before turbulence again begins to dilute it.

Then turbulence in the spiral arm mixes the oxygen-rich gas with other gas, diluting it.��That explains why gas that has just passed through a spiral arm is lowest in oxygen.

By spreading the oxygen around, however, the spiral arms help distribute the element far and wide so that oxygen eventually makes its way into future generations of stars and planets elsewhere in the galaxy.

Reference:��ArXiv:����

Read more: Galaxy’s rapid growth spurt may have spawned 3000 suns per year

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We already know the naked mole rat is an animal superhero: it is long-lived for an animal of its size, rarely gets cancer and shrugs off some kinds of pain. Now the East African rodent turns out to have a metabolic trick that allows it to survive very low oxygen levels with no apparent ill effects.

To investigate how well naked mole rats (Heterocephalus glaber) tolerate low oxygen concentrations, a team of biologists first put them in a chamber with just 5 per cent oxygen, less than a quarter the amount found in air. Such conditions kill mice within 15 minutes (and we wouldn’t survive either).

But naked mole rats just carry on as normal. The first test was stopped after 5 hours when nothing happened, says at the University of Illinois at Chicago. “We were blown away.”

Next the team put mole rats in pure nitrogen, with no oxygen at all. This kills mice in about a minute. People pass out after a breath or two of pure nitrogen, and would probably die in under 10 minutes.

The naked mole rats, however, survived for at least 18 minutes. They stopped breathing after a few minutes, but their hearts kept beating and as soon as they were put back in normal air they revived.

Resurrection rodent

“They come back to life without any apparent problems,” says team member of the Max Delbrück Center for Molecular Medicine in Berlin, Germany.

Diving mammals such as whales can hold their breath for over an hour. But between dives they breathe normal air at the surface and store oxygen in their tissues to help them survive.

Naked mole rats, by contrast, live in underground colonies of up to 300 animals where oxygen is likely to always be in short supply.

“They live in really challenging conditions,” says of Queen Mary, University of London, who studies mole rats, but wasn’t involved in the research. The tunnels that connect colonies to the surface are narrow and can get completely blocked by heavy rain, he says.

What’s more, the animals tend to huddle together in nesting chambers. “They like to pile together in a big heap of naked mole rats,” he says.

Metabolic trick

So how do they cope with the resulting lack of oxygen? Partly by minimising their need for it. Naked mole rats burn little energy heating their bodies, instead staying at the same temperature as their burrows – around 30 °C.

They also have a low metabolism and go into a sort of suspended animation in zero oxygen. But a clever metabolic trick helps them survive, too.

Animal cells get their energy from “burning” the simple sugar glucose. When there is no oxygen, these cells must use far more glucose to get the same amount of energy, and the process produces lactic acid. High lactic acid levels can kill cells, says team member , also at the Max Delbrück Center, so a feedback system soon kicks in to shut down the process.

But if cells use the sugar fructose instead, they can bypass this system and keep producing energy.

And that’s exactly what naked mole rats do: they release fructose into their bloodstream when oxygen drops too low, and the sugar is taken up by heart and brain cells to keep critical systems running. “Obviously, the naked mole rats have a secret way to deal with lactate build-up,” says Reznick.

In theory, people might be able to use this trick too. Our cells can make the pumps required to take up fructose and the enzymes for using it, but normally have few, if any, of these proteins. Lewin is keen to study freedivers to see if their breath-holding training boosts their cells’ ability to use fructose.

Some fish and turtles overwinter for months in ice-covered ponds with low oxygen levels, but the cold helps minimise their need for oxygen. Besides naked mole rats, the epaulette shark is one of the few animals known to survive being deprived of oxygen at normal temperatures.