Ancient microbes may have been producing oxygen through photosynthesis a billion years earlier than we thought, which means oxygen was available for living organisms very close to the origin of life on earth. In a new article in Heliyon, a researcher from Imperial College London studied the molecular machines responsible for photosynthesis and found the process may have evolved as long as 3.6 billion years ago.

The crystal structure of Photosystem I (PDB ID: 1JB0) [Credit: Elsevier]

The author of the study, Dr. Tanai Cardona, says the research can help to solve the controversy around when organisms started producing oxygen -- something that was vital to the evolution of life on earth. It also suggests that the microorganisms we previously believed to be the first to produce oxygen -- cyanobacteria -- evolved later, and that simpler bacteria produced oxygen first.

"My results mean that the process that sustains almost all life on earth today may have been doing so for a lot longer than we think," said Dr. Cardona. "It may have been that the early availability of oxygen was what allowed microbes to diversify and dominate the world for billions of years. What allowed microbes to escape the cradle where life arose and conquer every corner of this world, more than 3 billion years ago."

Photosynthesis is the process that sustains complex life on earth -- all of the oxygen on our planet comes from photosynthesis. There are two types of photosynthesis: oxygenic and anoxygenic. Oxygenic photosynthesis uses light energy to split water molecules, releasing oxygen, electrons and protons. Anoxygenic photosynthesis use compounds like hydrogen sulfide or minerals like iron or arsenic instead of water, and it does not produce oxygen.

Previously, scientists believed that anoxygenic evolved long before oxygenic photosynthesis, and that the earth's atmosphere contained no oxygen until about 2.4 to 3 billion years ago. However, the new study suggests that the origin of oxygenic photosynthesis may have been as much as a billion years earlier, which means complex life would have been able to evolve earlier too.

A culture of Synechocystis sp. PCC 6803, a type of unicellular Cyanobacteria [Credit: Elsevier]

Dr. Cardona wanted to find out when oxygenic photosynthesis originated. Instead of trying to detect oxygen in ancient rocks, which is what had been done previously, he looked deep inside the molecular machines that carry out photosynthesis -- these are complex enzymes called photosystems. Oxygenic and anoxygenic photosynthesis both use an enzyme called Photosystem I. The core of the enzyme looks different in the two types of photosynthesis, and by studying how long ago the genes evolved to be different, Dr. Cardona could work out when oxidative photosynthesis first occurred.

He found that the differences in the genes may have occurred more than 3.4 billion years ago -- long before oxygen was thought to have first been produced on earth. This is also long before cyanobacteria -- microbes that were thought to be the first organisms to produce oxygen -- existed. This means there must have been predecessors, such as early bacteria, that have since evolved to carry out anoxygenic photosynthesis instead.

"This is the first time that anyone has tried to time the evolution of the photosystems," said Dr. Cardona. "The result hints towards the possibility that oxygenic photosynthesis, the process that have produced all oxygen on earth, actually started at a very early stage in the evolutionary history of life -- it helps solve one of the big controversies in biology today."

One surprising finding was that the evolution of the photosystem was not linear. Photosystems are known to evolve very slowly -- they have done so since cyanobacteria appeared at least 2.4 billion years ago. But when Dr. Cardona used that slow rate of evolution to calculate the origin of photosynthesis, he came up with a date that was older than the earth itself. This means the photosystem must have evolved much faster at the beginning -- something recent research suggests was due to the planet being hotter.

"There is still a lot we don't know about why life is the way it is and how most biological process originated," said Dr. Cardona. "Sometimes our best educated guesses don't even come close to representing what really happened so long ago."

Dr. Cardona hopes his findings may also help scientists who are looking for life on other planets answer some of their biggest questions.

Source: Elsevier [March 06, 2018]

ETH scientists have been able to prove that a protein structure widespread in nature – the amyloid – is theoretically capable of multiplying itself. This makes it a potential predecessor to molecules that are regarded as the building blocks of life.

Lakes in volcanic surroundings could have been the breeding ground for the first biochemical compounds around 4 to 4.5 billion years ago [Credit: Dhilung Kirat/Wikimedia, ETH Zurich]

Long regarded as a biological aberration, amyloids are fibrous aggregates of short protein fragments. Amyloids have a bad reputation because they are thought to be the cause of multiple neurodegenerative diseases, including Alzheimer’s, Parkinson’s and Creutzfeldt–Jakob disease.

It was only recently that researchers discovered that amyloids appear as structural and functional building blocks in a wide range of life forms, from bacteria, yeast and fungi to humans. In vertebrates, they play a role in the production of the pigment melanin, while yeast cells use amyloid aggregates to form a kind of molecular memory.

Catalysts in prebiotic evolution

Composed of short peptides, amyloid fibres can accelerate chemical reactions in a similar way to enzymes; they have thus been viewed for several years as candidates for the first precursor molecules of life. Until now, however, an important chemical property was lacking in the theory of amyloids role in abiogenesis: self-replication.

Left: electron micrograph of an amyloid fibre. In green is a diagram of the sheet structure characteristic for amyloids, consisting of multiple short peptide chains [Credit: Jason Greenwald/ETH Zurich]

Early proponents of the amyloid hypothesis include ETH Professor Roland Riek and his senior assistant Jason Greenwald, from the Laboratory of Physical Chemistry. In an experiment, they have now been able to show that amyloids can serve as a chemical template for the synthesis of short peptides. And the critical point: “This ability also potentially applies to the amyloid itself – meaning the molecules can self-replicate,” says Riek. The researchers reported their findings in a study in Nature Communications.

Template for self-replication

The ability to self-replicate is regarded as an essential prerequisite for every early form of life. By proving that amyloids self-replicate, Riek and his team have not only highlighted another amazing aspect of this commonly underestimated protein, but also filled in a previously missing link in the amyloid hypothesis’ argument.

Almost two years earlier, the ETH scientists had already proven in an experiment that amyloid structures can spontaneously form with astounding ease – from simple amino acids that probably already existed when the Earth was still lifeless, and under reaction conditions that appear very plausible for the primordial soup.

The self-replication mechanism of amyloid fibres depicted schematically: piece by piece, specific amino acids (coloured building blocks) settle at the right site and chemically combine. During the process, the growing amyloid serves as a template for itself [Credit: Lukas Frey/ETH Zurich]

The same is true for the newly discovered peptide synthesis: “The reaction mechanism seems to be of a general nature. It is stable over a wide range of temperatures and salt concentrations, in both acidic and alkaline environments,” explains Greenwald.

This discovery strengthens the researchers’ opinion that early in evolutionary history, amyloids could have played a central role in the development of early life forms as information carriers and catalytic units.

Not just an RNA world

Until now, however, the most widespread idea for the molecular beginnings of life has been the RNA hypothesis, which sees ribonucleic acid (RNA) as the only key player in the prebiotic primordial soup. This is because, like the genetic material DNA, RNA molecules can code information, and are also able to self-replicate.

The ETH researchers are now picking away at the prevailing dogma of an RNA-based world. They think that the amyloid hypothesis is more plausible; firstly, because RNA molecules with a biological function are much larger and more complex, so they are unlikely to form spontaneously under prebiotic conditions. “Additionally, amyloids are much more stable than early nucleic acid polymers, and they have a much simpler abiotic synthesis route compared to the complexity of known catalytic RNAs,” says Greenwald.

Riek adds: “We will never be able to prove which is true – to do so, we would have to turn back the last 4 to 4.5 billion years of evolution. However, we suspect that it was not one, but multiple molecular processes with various predecessor molecules that were involved in the creation of life.”

Author: Michael Keller | Source: ETH Zurich [February 22, 2018]

In popular culture, asteroids play the role of apocalyptic threat, get blamed for wiping out the dinosaurs -- and offer an extraterrestrial source for mineral mining.

Credit: Pixabay

But for researcher Nicholas Hud, asteroids play an entirely different role: that of time capsules showing what molecules originally existed in our solar system. Having that information gives scientists the starting point they need to reconstruct the complex pathway that got life started on Earth.

Director of the NSF-NASA Center for Chemical Evolution at the Georgia Institute of Technology, Hud says finding molecules in asteroids provides the strongest evidence that such compounds were present on the Earth before life formed. Knowing what molecules were present helps establish the initial conditions that led to the formation of amino acids and related compounds that, in turn, came together to form peptides, small protein-like molecules that may have kicked off life on this planet.

"We can look to the asteroids to help us understand what chemistry is possible in the universe," said Hud. "It's important for us to study materials from asteroids and meteorites, the smaller versions of asteroids that fall to Earth, to test the validity of our models for how molecules in them could have helped give rise to life. We also need to catalog the molecules from asteroids and meteorites because there might be compounds there that we had not even considered important for starting life."

Hud will be a panelist at a press briefing "Asteroids for Research, Discovery, and Commerce" on February 17 at the 2018 annual meeting of the American Association for the Advancement of Science (AAAS) in Austin, Texas.

NASA scientists have been analyzing compounds found in asteroids and meteorites for decades, and their work provides a solid understanding for what might have been present when the Earth itself was formed, Hud says.

"If you model a prebiotic chemical reaction in the laboratory, scientists can argue about whether or not you had the right starting materials," said Hud. "Detection of a molecule in an asteroid or meteorite is about the only evidence everyone will accept for that molecule being prebiotic. It's something we can really lean on."

The Miller-Urey experiment, conducted in 1952 to simulate conditions believed to have existed on the early Earth, produced more than 20 different amino acids, organic compounds that are the building blocks for peptides. The experiment was kicked off by sparks inside a flask containing water, methane, ammonia and hydrogen, all materials believed to have existed in the atmosphere when the Earth was very young.

Nicolas Hud, director of the NSF-NASA Center for Chemical Evolution at the Georgia Institute of Technology [Credit: Fitrah Hamid, Georgia Tech]

Since the Miller-Urey experiment, scientists have demonstrated the feasibility of other chemical pathways to amino acids and compounds necessary for life. In Hud's laboratory, for instance, researchers used cycles of alternating wet and dry conditions to create complex organic molecules over time. Under such conditions, amino acids and hydroxy acids, compounds that differ chemically by just a single atom, could have formed short peptides that led to the formation of larger and more complex molecules -- ultimately exhibiting properties that we now associate with biological molecules.

"We now have a really good way to synthesize peptides with amino acids and hydroxy acids working together that could have been common on the early Earth," he said. "Even today, hydroxy acids are found with amino acids in living organisms -- and in some meteorite samples that have been examined."

Hud believes there are many possible ways that the molecules of life could have formed. Life could have gotten started with molecules that are less sophisticated and less efficient than what we see today. Like life itself, these molecules could have evolved over time.

"What we find is that these compounds can form molecules that look a lot like modern peptides, except in the backbone that is holding the units together," said Hud. "The overall structure can be very similar and would be easier to make, though it doesn't have the ability to fold into as complex structures as modern proteins. There is a tradeoff between the simplicity of forming these molecules and how close these molecules are to those found in contemporary life."

Geologists believe the Earth was very different billions of years ago. Instead of continents, there were islands protruding from the oceans. Even the sun was different, producing less light but more cosmic rays -- which could have helped power the protein-forming chemical reactions.

"The islands could have been potential incubators for life, with molecules raining down from the atmosphere," Hud said. "We think the key process that would have allowed these molecules to go to the next stage is a wet-dry cycling like what we are doing in the lab. That would have been perfect for an island out in the ocean."

Rather than a single spark of life, the molecules could have evolved slowly over time in gradual progression that may have taken place at different rates in different locations, perhaps simultaneously. Different components of cells, for example, may have developed separately where conditions favored them before they ultimately came together.

"There is something very special about peptides, nucleic acids, polysaccharides and lipids and their ability to work together to do something they couldn't have done separately," he said. "And there could have been any number of chemical processes on the early Earth that never led to life."

Knowing what conditions were like on the early Earth therefore gives scientists a stronger foundation for hypothesizing what could have taken place, and could offer hints to other pathways that may not have been considered yet.

"There are probably a lot more clues in the asteroids about what molecules were really there," said Hud. "We may not even know what we should be looking for in these asteroids, but by looking at what molecules we find, we can ask different and more questions about how they could have helped get life started."

Source: Georgia Institute of Technology [February 17, 2018]

Life as we know it originated roughly 3.5 to 4 billion years ago in the form of a prebiotic ("before life") soup of organic molecules that somehow began to replicate themselves and pass along a genetic formula. Or so goes the thinking behind the RNA World, one of the most robust hypotheses of the origin of life.

Researchers find that the amino acid arginine may have played a more important role in the chemical origins of life [Credit: University of California - Santa Barbara]

Researchers at UC Santa Barbara have now found evidence that the amino acid arginine (or its prebiotic world equivalent) may have been a more important ingredient in this soup than previously thought.

"People tend to think of arginine as not being prebiotic," said Irene Chen, a biophysicist whose research focuses on the chemical origins of life. "They tend to think of the simpler amino acids as being plausible, such as glycine and alanine." Arginine, by contrast, is relatively more complex, and was therefore thought to have entered the game at a later stage.

Primordial Earth, according to the RNA World theory, had the conditions to host several types of biomolecules, including nucleic acids (which become genetic material), amino acids (which eventually link to form the proteins that are responsible for structure and function of cells) and lipids (which store energy and protect cells). Under what circumstances and how these biomolecules worked together is a source of ongoing investigation for researchers of the origins of life.

For their investigation, the UCSB scientists analyzed a dataset of in vitro evolved complexes of proteins and aptamers (short RNA and DNA molecules that bind to specific target proteins).

"We were looking at the interface for which properties favored binding," said Celia Blanco, a postdoctoral researcher in the Chen Lab, and lead author of a paper that appears in the journal Current Biology. In vitro evolution was an important factor when selecting these evolutionarily independent complexes, she pointed out, to avoid the confounding effects resulting from biological evolution and to closely mimic the conditions of a prebiotic world.

"There are so many constraints in biology," said Chen, who also is a medical doctor. "Biologically evolved protein-DNA or protein-RNA interactions have to work inside a cell; that's not exactly going to be the case for the origins of life."

What the researchers found was that arginine was a player in many of the chemical interactions between proteins and aptamers.

"Of course, we expected it to be very important for electrostatic interactions because it's positively charged," Chen said, "but it was also the dominant amino acid for hydrophobic interactions, stacking interactions and these other different modes of interacting that other amino acids are more known for." To a lesser degree, lysine (another positively charged amino acid) also played significant roles in these interactions.

Among other reasons, arginine may have been overlooked because it is a relatively more difficult amino acid to synthesize.

"Usually people base the consensus of what is prebiotic and what is not on experiments," Blanco said. "And using what people believe are prebiotic conditions, arginine and lysine seem to be difficult to either synthesize or detect." But just because something such as arginine hasn't been produced in the laboratory experiments conducted so far, Blanco continued, doesn't mean it wasn't there.

The researchers are careful to point out that although the amino acid we call arginine was found to be important in the aptamer-protein binding interactions they examined, billions of years ago the biomolecule may not necessarily have been today's arginine but perhaps a positively charged primordial equivalent.

This development sheds more light on what might have been the ideal conditions for the rise of life. There are a variety of hypotheses -- from comets to hydrothermal vents to other environments -- that may have been favorable for the eventual evolution of cells, as well as several landmark experiments that bolster the RNA World idea.

"If we had found that glycine was really important for RNA-protein interactions -- and glycine is everywhere -- then that would not have been helpful for determining plausible conditions," said Chen. "But finding that arginine was important constrains the type of scenarios that could have given rise to the genetic code."

Author: Sonia Fernandez | Source: University of California - Santa Barbara [February 06, 2018]

One of the big evolutionary questions in life is how and why single cell organisms organised themselves to live in a group, thereby forming multicellular life forms.

The muliticellular algae, Tetrabaena socialis [Credit: Hisayoshi Nozaki and Yoko Arakaki]

Wits PhD student, Jonathan Featherston, of the Evolution of Complexity Laboratory at the University of the Witwatersrand, Johannesburg, has answered at least part of this question, by decoding the genomic sequence of one of the simplest of all multicellular organisms - the four-celled alga Tetrabaena socialis. His research has been published in Molecular Biology and Evolution.

Tetrabaena is a member of a lineage of green-algae known as the volvocine lineage. The lineage is a model lineage for understanding how multicellularity evolved. By studying the genome of this simple alga, a number of genetic mechanisms that control how cells divide were associated with the origin of multicellularity.

By painstakingly piecing together the whole genome sequence for the alga over a period of over two years, using various genome-sequencing methodologies, Featherston has identified the ubiquitin proteasomal pathway (UPP) as a process that plays a key role in the evolution of multicellularity. This pathway is involved in regulating many activities in cells by targeting proteins for destruction thereby maintaining a careful balance of proteins in cells.

"The UPP has been implicated in many human cancers and even as a potential target for treating cancers. From this study it seems that alterations to this pathway were important for how multicellularity evolved in these algae," says Featherston.

UPP is a complicated pathway that controls the cellular concentration of key proteins that drive cell division and it plays a role in many cellular functions. Featherston's study suggests that UPP may play a regulating how many divisions each species of volvocine undergoes through degradation of key molecules that control cell division.

"One of the earliest evolutionary adaptations in the volvocines was a modified cell cycle. The multicellular volvocines evolved a genetic program for controlling the number of divisions during reproduction where each species has a genetically programmed maximum number of divisions. Some will only divide twice during reproduction while others may divide 12 times," he says. "Normally people look a lot at how much of a key regulatory molecule is produced by a cell but here the interest is in the pathway that destroys these molecules. It's kind of the other side of how cellular processes are regulated."

Featherston compared the genome sequence of multicellular algae to their nearest single celled relative, in order to establish the genetic differences associated with the evolution of multicellularity. While overall, the the single celled and multicelled algae are very similar, he identified a small set of gene families (131) that were gained at the origin of multicellularity.

"We picked up some trends from this set of families. Many have developmental functions, which indicates that they probably are important for the evolution of multicellularity," he says.

Featherston's work shows that the evolution of multicellularity is associated with lineage-specific genetic developments.

"Multicellularity has evolved at least 25 times independently, but in all likelihood while certain general biological mechanisms - like cells-sticking together or modified cell cycles - may be shared, the actual genes driving these developments will mostly be unique to each lineage," he says. "Almost all the families that are found in other organisms can be found in a diverse array of unicellular organisms, suggesting that the genes that gave rise to multicellularity were derived from genes that were already present in the unicellular ancestor but may have been duplicated to form new genes that now have new functions."

Source: Wits University [February 02, 2018]

Extremophiles -- hardy organisms living in places that would kill most life on Earth -- provide fascinating insights into evolution, metabolism and even possible extraterrestrial life. A new study provides insights into how one type of extremophile, a heat-loving microbe that uses ammonia for energy production, may have been able to make the transition from hot springs to more moderate environments across the globe. The first-ever analysis of DNA of a contemporary heat-loving, ammonia-oxidizing organism, published in open-access journal Frontiers in Microbiology, reveals that evolution of the necessary adaptations may have been helped by highly mobile genetic elements and DNA exchange with a variety of other organisms.

Artemia salina, also known as a sea monkey, is a halophile that lives in habitats with high salt concentrations [Credit: De Agostini Picture Library/Getty Images]

Most extremophiles are microorganisms -- and many of the most extreme are archaea, an ancient group of single-celled organisms intermediate between the other two domains of life, bacteria and eukaryotes. Different archaea lineages are specialized to different extreme environments, including scalding hot springs, incredibly salty lakes, sunless deep-sea trenches and frigid Antarctic deserts. Only one branch, Thaumarchaeota, has managed to colonize very successfully the Earth's more hospitable places -- but scientists don't know why.

"Thaumarchaeota are found in very large numbers in virtually all environments, including the oceans, soils, plant leaves and the human skin," says Professor Christa Schleper from the University of Vienna, Austria, who guided and initiated the study. "We want to know what their secret is: billions of years ago, how did they adapt from hot springs, where it seems all archaea evolved, to more moderate habitats?"

As a starting point to answer this question, Professor Schleper and her team isolated a Thaumarchaeota species from a hot spring in Italy then sequenced and analyzed its genome. This represents the first genome analysis of the Nitroscaldus lineage -- a subgroup of heat-loving Thaumarchaeota that get their energy by oxidizing ammonia into nitrite.

The analysis revealed that the organism, Candidatus Nitrosocaldus cavascurensis, seems to represent the closest-related lineage to the last common ancestor of all Thaumarchaeota. Intriguingly, it has highly mobile DNA elements and seems to have frequently exchanged DNA with other organisms -- including other archaea, viruses and possibly even bacteria.

The ability to exchange genetic material could help this archaeon to rapidly evolve. "This organism seems prone to lateral gene transfer and invasion by foreign DNA elements," says Professor Schleper. "Such mechanisms may have also helped the ancestral lines of Thaumarchaeota to evolve and eventually radiate into moderate environments -- and N. cavascurensis may still be evolving through genetic exchange with neighboring organisms in its hot spring."

Many researchers assume that the first life forms on Earth evolved in hot springs. Further studies of this thermophile archaeon might help identify general mechanisms that enabled the first living cells, both bacteria and archaea, to conquer the world.

Source: Frontiers [January 26, 2018]

Rutgers scientists have found the "Legos of life" -- four core chemical structures that can be stacked together to build the myriad proteins inside every organism -- after smashing and dissecting nearly 10,000 proteins to understand their component parts.

Rutgers researchers identified a small set of simple protein building blocks (left) that likely existed at the earliest  stages of life's history. Over billions of years, these "Legos of life" were assembled and repurposed  by evolution into complex proteins (right) that are at the core of modern metabolism  [Credit: Vikas Nanda/Rutgers Robert Wood Johnson Medical School]

The four building blocks make energy available for humans and all other living organisms, according to a study published online today in the Proceedings of the National Academy of Sciences.

The study's findings could lead to applications of these stackable, organic building blocks for biomedical engineering and therapeutic proteins and the development of safer, more efficient industrial and energy catalysts -- proteins and enzymes that, like tireless robots, can repeatedly carry out chemical reactions and transfer energy to perform tasks.

"Understanding these parts and how they are connected to each other within the existing proteins could help us understand how to design new catalysts that could potentially split water, fix nitrogen or do other things that are really important for society," said Paul G. Falkowski, study co-author and a distinguished professor who leads the Environmental Biophysics and Molecular Ecology Laboratory at Rutgers University-New Brunswick.

The scientists' research was done on computers, using data on the 3D atomic structures of 9,500 proteins in the RCSB Protein Data Bank based at Rutgers, a rich source of information about how proteins work and evolve.

"We don't have a fossil record of what proteins looked like 4 billion years ago, so we have to take what we have today and start walking backwards, trying to imagine what these proteins looked like," said Vikas Nanda, senior author of the study and an associate professor in the Department of Biochemistry and Molecular Biology at Rutgers' Robert Wood Johnson Medical School, within Rutgers Biomedical and Health Sciences. "The study is the first time we've been able to take something with thousands of amino acids and break it down into reasonable chunks that could have had primordial origins."

The identification of four fundamental building blocks for all proteins is just a beginning. Nanda said future research may discover five or 10 more building blocks that serve as biological Legos.

"Now we need to understand how to put these parts together to make more interesting functional molecules," he said. "That's the next grand challenge."

The study's lead author is Hagai Raanana, a post-doctoral associate in the Environmental Biophysics and Molecular Ecology Program. Co-authors include Douglas H. Pike, a doctoral student at the Rutgers Institute for Quantitative Biomedicine, and Eli K. Moore, a post-doctoral associate in the Environmental Biophysics and Molecular Ecology Program.

Source: Rutgers University-New Brunswick [January 22, 2018]

RNA was probably the first informational molecule. Now chemists from Ludwig-Maximilians-Universitaet (LMU) in Munich have demonstrated that alternation of wet and dry conditions could have sufficed to drive the prebiotic synthesis of the RNA nucleosides found in all domains of life.

The basic constituents of the earliest RNA molecules may have formed in a geothermal environment,  such that seen here in Yellowstone National Park in Wyoming [Credit: Alliance/Mint Images]

"And the Earth was without form and void" -- before the emergence of life. Meanwhile, we know rather more about the early Earth, but how might the chemical structures that provide the basic subunits of today's hereditary molecules -- RNA and DNA -- have formed from simpler starting materials some 4 billion years ago? Under what conditions could these building blocks have then been linked into long chains that could not only encode information but also propagate it by self-reproduction? Many possible scenarios have been proposed for the phase of chemical evolution that preceded the emergence of the first biological cells. Now, researchers led by LMU chemist Professor Thomas Carell have extended these models by demonstrating a plausible route for the prebiotic synthesis of the 'nucleosides' that constitute the informational components of RNA.

Specifically, Carell and his colleagues have shown that nucleosides can be formed in a continuous process by exposing simple chemicals to the kinds of fluctuating physical conditions that would have prevailed in geothermally active areas characterized by volcanic activity on the early Earth. They begin with a mixture of formic acid, acetic acid, sodium nitrite and a few nitrogen-containing compounds, all of which have previously been shown to form from even simpler precursors under prebiotic conditions. The reaction mixture also contained nickel and iron, which are found in large amounts in the Earth's crust. The driving force for the chemical reactions is supplied by fluctuations in temperature and pH, together with wet/dry cycles, such as those that occur in the vicinity of periodically active hot springs or in strongly seasonal climates with alternating periods of precipitation and evaporation.

The core of the process is a series of reactions that gives rise to compounds called formamidopyrimidines, which can in turn be converted into the canonical purines (adenosine and guanosine) found in RNA. In a paper published last year, Carell and his team first described this FaPy pathway as a possible chemical scenario for the prebiotic synthesis of nucleosides. "This time around, we not only began with simpler precursor compounds, but chose conditions that would be expected to prevail in a plausible geological setting, such as hydrothermal springs on land," explains Sidney Becker, a PhD student in Carell's group and first author of the study. The paper has now appeared in one of the leading online, open-access journals, Nature Communications.

Notably, not only the canonical purine nucleosides found in RNA were synthesized in the new experiments, but also a whole series of closely related molecules. Even more strikingly, all of the modifications observed are known to occur in RNAs in all three domains of life -- Eukaryota (animals and plants), Bacteria and Archaea -- and are therefore essential components of functional genetic systems. Hence, they were most probably already present in the last common ancestor of all life forms. This in turn argues, says Becker, that these compounds must have been available on early Earth when biological evolution began.

Indeed, the authors of the new study suggest that the non-canonical nucleosides could have played a crucial role in the phase of chemical evolution that preceded the emergence of the 'RNA world' (the term refers to a hypothetical period during which RNA molecules are thought to have served as chemical catalysts, in addition to storing genetic information, in primordial cells). Seen in this light, the RNA modifications found in today's organisms represent molecular fossils that have continued to participate in vital biological functions for billions of years.

Source: Ludwig-Maximilians-Universität München [January 17, 2018]

Two wayward space rocks, which separately crashed to Earth in 1998 after circulating in our solar system's asteroid belt for billions of years, share something else in common: the ingredients for life. They are the first meteorites found to contain both liquid water and a mix of complex organic compounds such as hydrocarbons and amino acids.

A blue crystal recovered from a meteorite that fell near Morocco in 1998. The scale bar represents 200 microns  (millionths of a meter) [Credit: Queenie Chan/The Open University, UK]

A detailed study of the chemical makeup within tiny blue and purple salt crystals sampled from these meteorites, which included results from X-ray experiments at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), also found evidence for the pair's past intermingling and likely parents. These include Ceres, a brown dwarf planet that is the largest object in the asteroid belt, and the asteroid Hebe, a major source of meteorites that fall on Earth.

The study, published in the journal Science Advances, provides the first comprehensive chemical exploration of organic matter and liquid water in salt crystals found in Earth-impacting meteorites. The study treads new ground in the narrative of our solar system's early history and asteroid geology while surfacing exciting possibilities for the existence of life elsewhere in Earth's neighborhood.

"It's like a fly in amber," said David Kilcoyne, a scientist at Berkeley Lab's Advanced Light Source (ALS), which provided X-rays that were used to scan the samples' organic chemical components, including carbon, oxygen, and nitrogen. Kilcoyne was part of the international research team that prepared the study.

While the rich deposits of organic remnants recovered from the meteorites don't provide any proof of life outside of Earth, Kilcoyne said the meteorites' encapsulation of rich chemistry is analogous to the preservation of prehistoric insects in solidified sap droplets.

Blue halite and tweezer tips for scale [Credit: Dr. Queenie Hoi Shan Chan]

Queenie Chan, a planetary scientist and postdoctoral research associate at The Open University in the U.K. who was the study's lead author, said, "This is really the first time we have found abundant organic matter also associated with liquid water that is really crucial to the origin of life and the origin of complex organic compounds in space."

She added, "We're looking at the organic ingredients that can lead to the origin of life," including the amino acids needed to form proteins.

If life did exist in some form in the early solar system, the study notes that these salt crystal-containing meteorites raise the "possibility of trapping life and/or biomolecules" within their salt crystals. The crystals carried microscopic traces of water that is believed to date back to the infancy of our solar system -- about 4.5 billion years ago.

Chan said the similarity of the crystals found in the meteorites -- one of which smashed into the ground near a children's basketball game in Texas in March 1998 and the other which hit near Morocco in August 1998 -- suggest that their asteroid hosts may have crossed paths and mixed materials.

There are also structural clues of an impact -- perhaps by a small asteroid fragment impacting a larger asteroid, Chan said.

Artist's rendering of asteroids and space dust [Credit: NASA/JPL-Caltech]

This opens up many possibilities for how organic matter may be passed from one host to another in space, and scientists may need to rethink the processes that led to the complex suite of organic compounds on these meteorites.

"Things are not as simple as we thought they were," Chan said.

There are also clues, based on the organic chemistry and space observations, that the crystals may have originally been seeded by ice- or water-spewing volcanic activity on Ceres, she said.

"Everything leads to the conclusion that the origin of life is really possible elsewhere," Chan said. "There is a great range of organic compounds within these meteorites, including a very primitive type of organics that likely represent the early solar system's organic composition."

Chan said the two meteorites that yielded the 2-millimeter-sized salt crystals were carefully preserved at NASA's Johnson Space Center in Texas, and the tiny crystals containing organic solids and water traces measure just a fraction of the width of a human hair. Chan meticulously collected these crystals in a dust-controlled room, splitting off tiny sample fragments with metal instruments resembling dental picks.

"What makes our analysis so special is that we combined a lot of different state-of-the-art techniques to comprehensively study the organic components of these tiny salt crystals," Chan said.

Ceres, a dwarf planet in the asteroid belt pictured here in this NASA-produced false-colour image, may be  the source of organic matter found on two meteorites that crashed to Earth in 1998 [Credit: NASA]

Yoko Kebukawa, an associate professor of engineering at Yokohama National University in Japan, carried out experiments for the study at Berkeley Lab's ALS in May 2016 with Aiko Nakato, a postdoctoral researcher at Kyoto University in Japan. Kilcoyne helped to train the researchers to use the ALS X-ray beamline and microscope.

The beamline equipped with this X-ray microscope (a scanning transmission X-ray microscope, or STXM) is used in combination with a technique known as XANES (X-ray absorption near edge structure spectroscopy) to measure the presence of specific elements with a precision of tens of nanometers (tens of billionths of a meter).

"We revealed that the organic matter was somewhat similar to that found in primitive meteorites, but contained more oxygen-bearing chemistry," Kebukawa said. "Combined with other evidence, the results support the idea that the organic matter originated from a water-rich, or previously water-rich parent body -- an ocean world in the early solar system, possibly Ceres."

Kebukawa also used the same STXM technique to study samples at the Photon Factory, a research site in Japan. And the research team enlisted a variety of other chemical experimental techniques to explore the samples' makeup in different ways and at different scales.

Chan noted that there are some other well-preserved crystals from the meteorites that haven't yet been studied, and there are plans for follow-up studies to identify if any of those crystals may also contain water and complex organic molecules.

Kebukawa said she looks forward to continuing studies of these samples at the ALS and other sites: "We may find more variations in organic chemistry."

Author: Glenn Roberts Jr | Source: DOE/Lawrence Berkeley National Laboratory [January 10, 2018]

Chemists at The Scripps Research Institute (TSRI) have developed a fascinating new theory for how life on Earth may have begun.

Chemists find key chemical reactions that support life today could have been carried out with ingredients  likely present on the planet four billion years ago [Credit: Richard Bizley/Science Source]

Their experiments, described in the journal Nature Communications, demonstrate that key chemical reactions that support life today could have been carried out with ingredients likely present on the planet four billion years ago.

"This was a black box for us," said Ramanarayanan Krishnamurthy, PhD, associate professor of chemistry at TSRI and senior author of the new study. "But if you focus on the chemistry, the questions of origins of life become less daunting."

For the new study, Krishnamurthy and his coauthors, who are all members of the National Science Foundation/National Aeronautics and Space Administration Center for Chemical Evolution, focused on a series of chemical reactions that make up what researchers refer to as the citric acid cycle.

Every aerobic organism, from flamingoes to fungi, relies on the citric acid cycle to release stored energy in cells. In previous studies, researchers imagined early life using the same molecules for the citric acid cycle as life uses today. The problem with that approach, Krishnamurthy explains, is that these biological molecules are fragile and the chemical reactions used in the cycle would not have existed in the first billion years of Earth -- the ingredients simply didn't exist yet.

Leaders of the new study started with the chemical reactions first. They wrote the recipe and then determined which molecules present on early Earth could have worked as ingredients.

Credit: Greg Springsteen and Ramanarayanan Krishnamurthy

The new study outlines how two non-biological cycles -- called the HKG cycle and the malonate cycle -- could have come together to kick-start a crude version of the citric acid cycle. The two cycles use reactions that perform the same fundamental chemistry of a-ketoacids and b-ketoacids as in the citric acid cycle. These shared reactions include aldol additions, which bring new source molecules into the cycles, as well as beta and oxidative decarboxylations, which release the molecules as carbon dioxide (CO2).

As they ran these reactions, the researchers found they could produce amino acids in addition to CO2, which are also the end products of the citric acid cycle. The researchers think that as biological molecules like enzymes became available, they could have led to the replacement of non-biological molecules in these fundamental reactions to make them more elaborate and efficient.

"The chemistry could have stayed the same over time, it was just the nature of the molecules that changed," says Krishnamurthy. "The molecules evolved to be more complicated over time based on what biology needed."

"Modern metabolism has a precursor, a template, that was non-biological," adds Greg Springsteen, PhD, first author of the new study and associate professor of chemistry at Furman University.

Making these reactions even more plausible is the fact that at the center of these reactions is a molecule called glyoxylate, which studies show could have been available on early Earth and is part of the citric acid cycle today (called the "Glyoxylate shunt or cycle").

Krishnamurthy says more research needs to be done to see how these chemical reactions could have become as sustainable as the citric acid cycle is today.

Source: The Scripps Research Institute [January 08, 2018]

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An experiment mimicking our early solar system reveals that the sugar ribose, the 'R' in 'RNA,' can arise in the icy grains of comets. The origin of life on Earth has been a matter of intense debate throughout human history. Even today, scientists don’t know whether the molecular building blocks of life were created on Earth or whether they were brought here by comets and meteorites. This is obviously hugely important – if they were delivered to Earth then it seems plausible that they may have been transported to other planets, too. [...]

By Christian Schroeder University of Stirling 4-8-16

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