Tag Archives: phosphorus

Phosphate compounds may have arrived on Earth delivered by comets, such as comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/NAVCAM

Key ingredient for life on Earth may have come from outer space

Phosphates, essential ingredients for DNA-based life forms, may have originated from space, according to a new study that recreated the formation of the molecules in a laboratory setting. The life-seeding phosphates would have then made their way to Earth through asteroids and comets that impacted the planet billions of years ago.

Phosphate compounds may have arrived on Earth delivered by comets, such as comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/NAVCAM.

Without phosphates and diphosporic acid, living things wouldn’t be able to synthesize DNA. They are the main components of chromosomes, thread-like structures in which the DNA is packaged. Phosphorus is also part of adenosine triphosphate (ATP), which stores energy in the cell and powers cellular processes. Bones and teeth are also made up of phosphorus.

A long-standing debate among scientists is whether these chemical compounds were forged on Earth or someplace else in the universe, hitching a ride on cosmic bodies that collided with our planet.

Although the debate sounds impossible to solve, researchers at the University of Hawaii at Manatoa have now offered compelling evidence that phosphates can be generated in space.

For their experiment, the researchers worked with the chemical phosphine, which is derived from phosphorus and can be found in the atmospheres of planets such as Jupiter or Saturn, but also those of comets such as the famous 67P/Churyumov-Gerasimenko, explored by the Rosetta spacecraft in 2016.

First, the team recreated icy grains — the kind typically found in interstellar space — in a vacuum chamber where the temperature sat  just 5 degrees Kelvin above absolute zero (-450°F/-267.7°C). Then, they added water, carbon dioxide and — very carefully because it is highly toxic — phosphine. Finally, the researchers fired ionized radiation — the kind found in cosmic rays — at this, triggering chemical reactions that formed phosphoric acid and diphosphoric acid.

“On Earth, phosphine is lethal to living beings,” said Andrew Turner, lead author of the study in Nature Communications, in a statement. “But in the interstellar medium, an exotic phosphine chemistry can promote rare chemical reaction pathways to initiate the formation of biorelevant molecules such as oxoacids of phosphorus, which eventually might spark the molecular evolution of life as we know it.”

In deep space, it’s reasonable to assume such nanoparticles became embedded in large objects like asteroids and comets, which would have eventually made their way to Earth.

“Since comets contain at least partially the remnants of the material of the protoplanetary disk that formed our solar system, these compounds might be traced back to the interstellar medium wherever sufficient phosphine in interstellar ices is available,” said Cornelia Meinert of the University of Nice.

The findings appeared in the journal Nature Communications.

The forests won’t fix our CO2 problem — in fact, they’ll scrub less than we assumed

Carbon dioxide absorption by growing biosphere may have been overestimated up to now, a new study concludes. This is due to previous estimates not taking into account the limiting factor of essential nutrients on plant development.

Image via Pixabay.

One effect of rising concentrations of CO2 in our atmosphere is that plants have more of the gas — a prime source of carbon — to metabolize, improving growth rates. It also raises average temperatures in cold areas, promoting plant growth. Satellite imagery has shown that while growth has declined in some areas, our planet is getting greener overall.

Climate scientists have pointed out that this increased quantity of plants will be able to scrub even more CO2 out of the atmosphere, forming a natural carbon sink, and helping mitigate our emissions. But they have overestimated just how much the biosphere will grow, and thus how much more carbon it will soak. By testing the effect of higher CO2 levels on forests growing in tropical and subtropical soils, a team from the Western Sydney University in Australia has found that the biosphere will likely grow less than what previous estimates have projected.

Plenty of carbon, scarce phosphorus

The team, led by David Ellsworth of Western Sydney University in Australia, says that forests will absorb around a tenth less CO2 than previously expected, meaning CO2 levels will rise even faster than our current models predict. The main limiting factor opposing CO2’s fertilizing effect is the lack of phosphorous in tropical and subtropical regions, they explain.

To determine how much the biosphere will grow, the team artificially raised CO2 levels in six plots of a mature eucalyptus forest near Sydney, which were growing in characteristically phosphorus-poor soil. The plots were covered in a mix of individuals of diverse species and ages.

Previous similar work in temperate forests (whose soils are much richer in phosphorus) found that CO2 increase could boost growth by as much as 20%. Ellsworth’s team found no evidence of growth boost in their plots at all. They attribute this difference to the limiting effect of phosphorous (a key nutrient) on growth. The results are backed by previous results, showing plant growth in the past 30 years didn’t see as much an increase as we estimated.

Another (very) limiting factor is human activity. Although some forests will grow faster if left to their own devices, we have a pretty consistent habit of cutting them down. Martin Brandt et al. show that while there’s overall more woody vegetation in Africa, the effects of warmer climate and rising levels of CO2 are offset by deforestation for raw materials and arable land in highly populated, humid areas, leading to a decrease in woody vegetation for these regions. The biggest increase in forests was seen in dry areas with low human populations, but it’s unclear if this makes up for the losses in vegetation elsewhere.

Ellsworth also points out that an increase in plant growth doesn’t necessarily translate to an increase in CO2 absorption and storage by plants.

Where does this leave us? Well, while it would be a nice turn of events it seems unlikely that the trees will clean our mess. So overall the situation takes a turn for the worse. Our best bet, as up to now, is to limit emissions and find ways to sequester CO2. In the meantime, we should also try as much as possible to mitigate the damage.

The full paper “Elevated CO2 does not increase eucalypt forest productivity on a low-phosphorus soil” has been published in the journal Nature Climate Change.

 

Illustration of early Earth. Peter Sawyer / Smithsonian Institution.

Meteorites crashing into early Earth might have supplied all the precious biocompatible phosphorus

Illustration of early Earth. Peter Sawyer / Smithsonian Institution.

Illustration of early Earth. Peter Sawyer / Smithsonian Institution.

Life on this planet has been remarkable in its ability to diverge into so many directions. Plants, bacteria, blue whales, triceratops, tardigrades, humans. But all of these millions of species of life — some expired, others still around — are built from the same six essential elemental ingredients: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. Some of these elements were here from the very beginning when the planet formed its crust. The origin of at least one of these critical elements for life, phosphorus, is still very debatable though. Was it always here or did it arrive later ferried by meteorites and other cosmic bodies which impacted the ancient Earth? A new research seems to point to the latter conclusion, and how they got there is interesting — to say the least.

Connecting the dots

Phosphorus, the 11th most common element on earth, is essential for the creation of DNA, cell membranes, and for bone and teeth formation in humans. It is vital for food production since it is one of three nutrients (nitrogen, potassium and phosphorus) used in commercial fertilizer. Phosphorus cannot be manufactured or destroyed, and there is no substitute or synthetic version of it available.

 

 

For all its life bearing properties, though, the vast majority of phosphorus on Earth is in the form of inert phosphates which are insoluble in water and hence can’t react with organic molecules. How is it that something so essential and ubiquitous in biochemistry is so rare in Earth’s crust?

Image of schreibersite grain present in a thin-section of the enstatite meteorite, KLE 98300. Credit: Virginia Smith, UA Lunar & Planetary Laboratory

Image of schreibersite grain present in a thin-section of the enstatite meteorite, KLE 98300. Credit: Virginia Smith, UA Lunar & Planetary Laboratory

One possible explanation might lie in schreibersite [(Fe, Ni)3P], a mineral commonly found in meteorites ranging from chondrites to stony-iron pallasites. In 2004, Matthew Pasek, then an astrobiologist and geochemist from the University of South Florida, proposed that this mineral could be the original source of life-forming phosphorus. That’s because schreibersite contains a phosphorus ion bounded to a metal, hence it’s more reactive.

This hypothesis has been very difficult to test, however. Naturally-formed schreibersite is very difficult to source or expensive if bought from private meteorite collectors. So, Pasek and colleagues decided its best to synthesize it.

Natural schreibersite is made of iron, phosphorus and nickel, but most experiments use a synthetic schreibersite that only has iron and phosphorus. This variation is easily sourced as a byproduct of iron manufacturing.

Previously, scientists found that the mineral reactors with organics to form chemical bonds with oxygen — one of the first steps required for phosphorus’ integration in biological systems. This seems to validate Pasek’s hypothesis, however critics were quick to note that since it doesnt’ have nickel, there’s no cigar. Nickel, some claim, might alter the mineral’s chemistry and make it non-reactive.

Finally, Pasek and his colleagues at University of Arizona have addressed this criticism by developing a synthetic form of schreibersite that includes nickel, as described in a recent paper published in the journal Physical Chemistry Chemical Physics.

After exposing the nickel-rich mineral to water, phosphorus–oxygen (P–O) bonds formed on the surface of the schreibersite. Phosphorus bioavailability confirmed!

Pasek next to a tube that contains a meteorite sample dissolved in fresh water. Credit: University of Arizona

Pasek next to a tube that contains a meteorite sample dissolved in fresh water. Credit: University of Arizona

“Biological systems have a phosphorus atom surrounded by four oxygen atoms, so the first step is to put one oxygen atom and one phosphorous atom together in a single P–O bond,” Pasek explains.

Terry Kee, a geochemist at the University of Leeds and president of the Astrobiology Society of Britain, has conducted his own extensive work with schreibersite and, along with Pasek, is one of the original champions of the idea that it could be the source of life’s phosphorus.

“The bottom line of what [La Cruz and Pasek] have done is that it appears that this form of nickel-flavored synthetic schreibersite reacts pretty much the same as the previous synthetic form of schreibersite,” said Terry Kee, a geochemist at the University of Leeds and president of the Astrobiology Society of Britain, who was not involved in this study.

Pasek says meteorites would have impacted shallow pools of water that dotted ancient Earth. Subjected to evaporation and rehydration cycles, these pools would have offered the necessary conditions for the phosphorus to leach out of the mineral. Specifically, as the mineral dries, molecules join together into longer chains, but when the mineral is wet again the chains become mobile, bumping into other chains. When the pool dries out again, the chains bond and build ever larger structures.

“The reactions need to lose water in some way in order to build the molecules that make up life,” says Pasek. “If you have a long enough system with enough complex organics then, hypothetically, you could build longer and longer polymers to make bigger pieces of RNA. The idea is that at some point you might have enough RNA to begin to catalyze other reactions, starting a chain reaction that builds up to some sort of primitive biochemistry, but there’s still a lot of steps we don’t understand.”

We’re not done yet, though. Kee points out that besides meteorites, hydrothermal vents might also be a viable source. Research so far suggests that deep sea volcanic vents can produce iron-nickel alloys like awaruite. Though we haven’t yet, it’s possible some day we’ll discover schreibersite in some of these vents. Maybe, both sources worked together.

“If it could be shown that schreibersite can be produced in the conditions found in vents—and I think those conditions are highly conducive to forming schreibersite—then you’ve got the potential for a lot of interesting phosphorylation chemistry to take place,” says Kee.

 

 

transmission electron micrograph of the bacterium strain GFAJ-1+As/-P GFAJ-1 shows internal vacuole-like structures in an undated photograph released by NASA

New study debunks preposterous claims of arsenic-thriving bacteria

In 2010, a NASA study published in the journal Science heralded the discovery of a bacteria, called GFAJ-1, which the authors at the time claimed it substitutes arsenic for phosphorus to survive. This contravened with the elemental recipe for life, where phosphorus is essential, stirring a wave of controversy within scientific community, as it would mandate a reformulation of the basic requirements for life on Earth. Recently, two separate and independent studies found that the claims were erroneous, disproving the paper.

transmission electron micrograph of the bacterium strain GFAJ-1+As/-P GFAJ-1 shows internal vacuole-like structures in an undated photograph released by NASA

transmission electron micrograph of the bacterium strain GFAJ-1+As/-P GFAJ-1 shows internal vacuole-like structures in an undated photograph released by NASA.

The bacterium was found in Mono Lake, California. The lake doesn’t have any outlet to the ocean, which has lead along many thousand of years to an unusually salty body of water with high arsenic and mineral levels. Thus, a totally unique ecosystem was also formed. It’s  these truly unique conditions that sparked NASA’s interest, as it resembles patches of Mars or even early Earth.

In the lake, scientists discovered the GFAJ-1 bacteria, which was found to be able to survive despite having arsenic in its DNA and cell membranes instead of phosphorus – a controversial claim, by all means.

Science has found that there are six critical elements indispensably required for life: carbon, hydrogen, nitrogen, oxygen, phosphorous and sulphur. Arsenic, though rather similar to sulphur, is not only missing from the aforementioned list, but poisonous for most living organisms. So, you can imagine what kind of uprising the claim that an organism which incorporates poison into its DNA stirred into the scientific community at the time. It had alien written all over it, and enthusiasts were quick to jump on the bandwagon.

From extraterrestrial back to terrestrial

The claim had to be confirmed by other separate, independent studies before it could have been deemed as a discovery. Two were recently published, both of which found flaws in the original paper.

One of the papers found that the bacterium was not really replacing phosphorus with arsenic throughout its DNA, but “may sometimes assimilate arsenate into some small molecules in place of phosphate.” The other paper tackled another significant claim; in the original paper from 2010, the authors stressed that the phosphor present in the samples was simply too low to accommodate life at all. The group, lead by Tobias Erb from the Institute of Microbiology, found that organism was incapable of surviving without some amount of the substance.

Some scientists, and science journalists alike, were quick to bash the authors of the original paper, lead by Felisa Wolfe-Simon of NASA’s Astrobiology Institute. Phrases like “bad science”, “sloppy research” and the likes were thrown a lot these past few days. I, for one, don’t agree. While I believe that the research could have been checked and even interpreted a lot more conservative, the finding is still important due to the very nature of this extraordinary organism. All the worse was for the better, if you’d like to see the half full side of the glass, since more attention has been directed towards it.

GFAJ-1 is a veritable extremophile. A survivor. It “is likely adept at scavenging phosphate under harsh conditions, which would help to explain why it can grow even when arsenic is present within the cells,” one of the journal entries reads; and what follows couldn’t better resonate with my own thoughts:

“The scientific process is a naturally self-correcting one, as scientists attempt to replicate published results,” it added.

Both studies were published in the journal Science.

source: 1 and 2

The interior spongy bone of a rabbit femoral head. (c) Yale University

New MRI technique allows 3-D imaging of non-living material

Researchers at Yale University have successfully mange to utilize a novel MRI technique to 3-D image the insides of hard and soft solids, like bone and tissue, opening the way for a new array of applications, like previously difficult to image dense objects.

 The interior spongy bone of a rabbit femoral head. (c) Yale University Typically, magnetic resonance imaging (MRI) can produce a 3-D image of an object by using an array of powerful magnets and bursts of radio waves which target hydrogen atoms in the respective object. These hydrogen atoms absorb the radio waves, and then emit them back, revealing their precise location. A computer then interprets these signals and “paints” a picture. It’s a very simple, yet highly productive technique, which is why MRI is so popular, especially in the medical field. However, it’s greatest disadvantage is that it needs a lot of hydrogen to read an object, and as such it only works on water-rich materials, like flesh or the human brain. Bones, very tough materials, rocks or basically almost anything that’s non-living can’t be imaged through MRI, until so far at least.

The Yale scientists have developed a new method for MRI imaging, which they call “quadratic echo MRI of solids,” that works by targeting phosphorus atoms instead of hydrogen atoms. A more complicated sequence of radio waves pulses are fired for them to interact with phosphorus, a fairly abundant element in many biological samples, allowing for high-spatial-resolution imaging.

In the paper published recently in the journal PNAS, the Yale team report on various experiments designed to generated 3D MRIs using the phosphorus technique. They thus performed high-resolution 3D images of ex vivo animal bone and soft tissue samples, including cow bone and mouse liver, heart, and brains.

“This study represents a critical advance because it describes a way to ‘see’ phosphorus in bone with sufficient resolution to compliment what we can determine about bone structure using x-rays,” said Insogna, a professor at Yale School of Medicine and director of the Yale Bone Center. “It opens up an entirely new approach to assessing bone quality.”

The researchers say this new type of MRI would complement traditional MRI, not supplant it. MRI of solids should also be possible with elements other than phosphorus, they say.

The researchers believe this new type of MRI imaging should be used to complement the traditional MRI already in place, and claim that MRI imaging of solids through other elements other than hydrogen or phosphorus should be possible. The quadratic echo MRI technique, however, can’t be used on living beings – for one it generates way too much heat. Immediate applications include archaeology, geology, oil drilling.