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This goes in to thorough detail but it might really help some of you if you lack understanding or you want something extra to add to an essay.

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super cool guys check it out

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Climate scientists have not been properly accounting for what plants do at night, and that, it turns out, is a mistake. A new study from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has found that plant nutrient uptake in the absence of photosynthesis affects greenhouse gas emissions to the atmosphere.

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Climate scientists have not been properly accounting for what plants do at night, and that, it turns out, is a mistake. A new study from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has found that plant nutrient uptake in the absence of photosynthesis affects greenhouse gas emissions to the atmosphere.

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Photosynthesis in plants is nature's way to turn light into chemically usable energy. A growing branch of research has the goal to artificially imitate the photosystem of chloroplasts, but has mostly failed to achieve a comparable efficiency.

The chloroplast is an organelle found in plants and cyanobacteria that conducts photosynthesis to convert solar energy into the "energy currency" of life - adenosine triphosphate (ATP). The main parts of photosynthesis are carried out by protein complexes termed photosystem I and photosystem II. Water splitting in the final step generates ATP and oxygen, accompanied by the reduction of nicotinamide adenine dinucleotide phosphate (NADP) to nicotinamide adenine dinucleotide phosphate (NADPH).

Unfortunately, this system uses merely the visible spectrum of light, thereby excluding almost 90% of the sun's energy. Strategies to mimic the photosynthetic processes try to circumvent this by using light-harvesting nanomaterials for converting UV-light into visible light, which in turn can be absorbed normally by the photosystem.

Such conversion strategies so far only generated blue light, resulting in a poor match of the absorption spectrum of chloroplasts. Researchers from South China Agricultural University, P.R. China and Georgia Southern University, USA have taken a different route: Yingliang Liu, Bingfu Lei, and co-workers describe how carbon quantum dots can be integrated into the photosystem to achieve an almost 3-fold increased adenosine triphosphate production by converting UV-light into blue and red visible light.

The scientists generate light-harvesting carbon dots from the plant Phellodendron chinense by hydrothermal extraction with ethanol. The carbon dots are derived from chlorophyllic porphyrins - an aromatic core with porphyrins on the outside results in strong UV-light absorption combined with emission of both blue and red light. Bringing the dots into contact with the outer membrane of chloroplasts promotes photosynthesis both in vitro and in the leaves of living Rome lettuce.

Visit Advanced Functional Materials to learn more about this exciting finding at the interface of nanotechnology and plant biology and other outstanding research.

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Carbon Going Green: Quantum Dot Enhanced Photosynthesis - Advanced Science News

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Photosynthesis in plants is nature's way to turn light into chemically usable energy. A growing branch of research has the goal to artificially imitate the photosystem of chloroplasts, but has mostly failed to achieve a comparable efficiency.

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posted by Merit

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The latest important clue comes from Heliobacterium modesticaldum, which has the distinction of being the simplest known photosynthetic bacterium. Its reaction center, researchers think, is the closest thing available to the original complex. Ever since the biologists Kevin Redding, Raimund Fromme and Christopher Gisriel of Arizona State University, in collaboration with their colleagues at Penn State, published the crystallographic structure of that protein complex in a July edition of Science, experts have been unpacking exactly what it means for the evolution of photosynthesis. "It's really a window into the past," Gisriel said.

"This is something we've been waiting for for 15 years," Nitschke said.

In Search of a Common Ancestor

At first, most scientists did not believe that all the reaction centers found in photosynthetic organisms today could possibly have a single common ancestor. True, all reaction centers harvest energy from light and lock it into compounds in a form that's chemically useful to cells. To do this, the proteins pass electrons along a transfer chain of molecules in a membrane, as though skipping along a series of stepping stones. Each step releases energy that's ultimately used down the line to make energy-carrier molecules for the cell.

But in terms of function and structure, the photosystem reaction centers fall into two categories that differ in almost every way. Photosystem I serves mainly to produce the energy carrier NADPH, whereas photosystem II makes ATP and splits water molecules. Their reaction centers use different light-absorbing pigments and soak up different portions of the spectrum. Electrons flow through their reaction centers differently. And the protein sequences for the reaction centers don't seem to bear any relation to each other.

Both types of photosystem come together in green plants, algae and cyanobacteria to perform a particularly complex form of photosynthesis - oxygenic photosynthesis - that produces energy (in the form of ATP and carbohydrates) as well as oxygen, a byproduct toxic to many cells. The remaining photosynthetic organisms, all of which are bacteria, use only one type of reaction center or the other.

So it seemed as though there were two evolutionary trees to follow - that was, until the crystal structures of these reaction centers began to emerge in the early 1990s. Researchers then saw undeniable evidence that the reaction centers for photosystems I and II had a common origin. Specific working components of the centers seemed to have undergone some substitutions during evolution, but the overall structural motif at their cores was conserved. "It turned out that big structural features were retained, but sequence similarities were lost in the mists of time," said Bill Rutherford, the chairman in biochemistry of solar energy at Imperial College London.

"Nature has played small games to change some of the functions of the reaction center, to change the mechanisms by which it works," Redding added. "But it hasn't rewritten the playbook. It's like having a cookie-cutter design for a house, building that same house over and over again, and then changing how the rooms are arranged, how the furniture is positioned. It's the same house, but the functions inside are different."

Researchers began to make more detailed comparisons between the reaction centers, searching for clues about their relationship and how they diverged. Heliobacteria have brought them a few steps closer to that goal.

Harkening Back to an Earlier Time

Since it was discovered in the soil around Iceland's hot springs in the mid-1990s, H. modesticaldum has presented researchers with an interesting piece of the photosynthesis puzzle. The only photosynthetic bacterium in a family with hundreds of species and genera, heliobacteria's photosynthetic equipment is very simple - something that became even more apparent when it was sequenced in 2008. "Its genetics are very streamlined," said Tanai Cardona, a biochemist at Imperial College London.

Heliobacteria have perfectly symmetrical reaction centers, use a form of bacteriochlorophyll that's different from the chlorophyll found in most bacteria, and cannot perform all the functions that other photosynthetic organisms can. For instance, they cannot use carbon dioxide as a source of carbon, and they die when exposed to oxygen. In fact, their structure took nearly seven years to obtain, partly because of the technical difficulties in keeping the heliobacteria insulated from oxygen. "When we first started working on it," Redding said, "we killed it more than once."

Taken together, "heliobacteria have a simplicity in their organization that's surprising compared to the very sophisticated systems you have in plants and other organisms," said Robert Blankenship, a leading figure in photosynthesis research at Washington University in St. Louis. "It harkens back to an earlier evolutionary time."

Its symmetry and other features "represent something quite stripped down," Redding added, "something we think is closer to what that ancestral reaction center would have looked like three billion years ago."

A Glimpse of the Past

After carefully taking images of the crystallized reaction centers, the team found that although the reaction center is officially classified as type I, it seemed to be more of a hybrid of the two systems. "It's less like photosystem I than we thought," Redding said. Some people might even call it a "type 1.5," according to Gisriel.

One reason for that conclusion involves greasy molecules called quinones, which help transfer electrons in photosynthetic reaction centers. Every reaction center studied so far uses bound quinones as intermediates at some point in the electron transfer process. In photosystem I, the quinones on both sides are tightly bound; in photosystem II, they are tightly bound on one side, but loosely bound on the other. But that's not the case in the heliobacterium reaction center: Redding, Fromme and Gisriel did not find permanently bound quinones among the electron transfer chain's stepping stones at all. That most likely means its quinones, although still involved in receiving electrons, are mobile and able to diffuse through the membrane. The system might send electrons to them when another, more energetically efficient molecule isn't available.

This finding has helped the research team deduce what early reaction centers may have been doing. "Their job was likely to reduce mobile quinones," Redding said. "But they weren't doing a very good job of it." In the researchers' scenario, tightly bound quinone sites are a more recent adaptation, and today's type I and type II reaction centers represent alternative evolutionary strategies, embraced by different lineages of organisms, for improving on the ancestral system's sloppy, less-than-ideal work.

"But then the question is, why has nature changed this kind of electron transfer chain?" Fromme asked. His work supports the hypothesis that it might have something to do with oxygen.

When an organism is exposed to too much light, electrons build up in the transfer chain. If oxygen is around, this buildup can lead to a harmfully reactive oxygen state. Adding a firmly bound quinone to the complex not only provides an additional slot to deal with potential traffic jams; the molecule, unlike others used in the transfer chain, also does not pose any risk of producing that deleterious form of oxygen. A similar explanation works for why reaction centers became asymmetric, Gisriel added: Doing so would have added more stepping stones as well, which would have similarly buffered against damage caused by the accumulation of too many electrons.

One of the researchers' next steps is to put time stamps on when this asymmetry and these tightly bound quinones came into the picture, which would help them determine when oxygenic photosynthesis became possible.

All Roads Lead to Oxygen

Cardona, who was not involved in the recent study but has begun interpreting its results, thinks he may have found a hint in the heliobacterium reaction center. According to him, the complex seems to have structural elements that would have later lent themselves to the production of oxygen during photosynthesis, even if that wasn't their initial purpose. He found that a particular binding site for calcium in the heliobacteria's structure was identical to the position of the manganese cluster in photosystem II, which made it possible to oxidize water and produce oxygen.

"If the ancestral [calcium] site at some later stage turned into the manganese cluster," Cardona said, "that would suggest that water oxidation was involved in the earliest events in the divergence between type I and type II reaction centers." That, in turn, would mean oxygenic photosynthesis was far more ancient than expected. Scientists have commonly supposed that oxygenic photosynthesis appeared shortly before the Great Oxygenation Event, when oxygen began to build up in Earth's atmosphere and caused a mass extinction 2.3 to 2.5 billion years ago. If Cardona is right, it may have evolved nearly a billion years earlier, shortly after photosynthesis made its debut.

That timing would have been early enough to predate the cyanobacteria typically credited as the first organisms to perform oxygenic photosynthesis. According to Cardona, it may be the case that a lot of bacteria could do it, but that after mutations, divergences and other events, only cyanobacteria retained the ability. (Cardona published a paper this year citing other molecular evidence for this hypothesis. He has not yet formally presented arguments about the potential link involving calcium for peer review, but he has written about the idea in blog posts on his website and on a scientific networking site for researchers, and he recently began working on a paper about it.)

That hypothesis contradicts one of the widely held ideas about the origins of photosynthesis: that species incapable of photosynthesis suddenly obtained the capacity through genes passed laterally from other organisms. According to Cardona, in light of the new discoveries, horizontal gene transfer and gene loss may both have played a role in the diversification of reaction centers, although he suspects that the latter may have been responsible for the earliest events. The finding, he said, might suggest that "the balance skews toward the gene-loss hypothesis" - and toward the idea that photosynthesis was an ancestral characteristic that some groups of bacteria lost over time.

Not everyone is so sure. Blankenship, for one, is skeptical. "I don't buy that," he said. "I don't see any data here that suggests that oxygenic photosynthesis occurred that much earlier." To him, the work by Redding, Fromme and their collaborators has not answered these questions; it has only conjectured about what may have happened. To solve that puzzle, scientists will need the reaction center structures of other bacteria, so they can continue evaluating the structural differences and similarities to refine the twisting roots of their evolutionary trees.

"I think it's entirely a possibility that what [Cardona] is saying is correct," Gisriel said, "but I also think the field should sit with it for a while, do some more analysis and see if we understand more about how this structure works."

Going the Synthetic Route

Some researchers aren't waiting for the publication of the next structure. This one took seven years, after all. They're pursuing synthetic experimentation instead.

Rutherford and his colleagues, for example, are using a "reverse evolution" technique: They hope to predict the sequences of missing-link reaction centers, using structural information like Redding's to gain an understanding of their architecture. They then plan to synthesize those hypothetical ancestral sequences and test how they evolve.

Meanwhile, Redding and his team have just begun artificially converting the symmetric reaction center of heliobacteria into an asymmetrical one, following in the footsteps of two researchers in Japan, Hirozo Oh-Oka of Osaka University and Chihiro Azai of Ritsumeikan University, who have spent more than a decade doing this in another type of photosynthetic bacterium. The groups believe their work will clarify how these adaptations would have occurred in real life in the distant past.

Twenty years ago, Nitschke stopped working on the evolution of photosynthesis and turned his attention to other problems. "It seemed so hopeless," he said. But the research done by Redding, his team and these other groups has rekindled those ambitions. "As they say, your first love always stays with you," Nitschke said. "I'm really excited about this new structure and plan to go back to thinking about all this again."
This article was reprinted on Wired.com.

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Simple Bacteria Offer Clues to the Origins of Photosynthesis | Quanta Magazine

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The latest important clue comes from Heliobacterium modesticaldum, which has the distinction of being the simplest known photosynthetic bacterium. Its reaction center, researchers think, is the closest thing available to the original complex.

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Artificial photosynthesis reversing climate change 

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Artificial photosynthesis reversing climate change 

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posted by Dias

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Florida researchers announced last week that they had synthesized a material that could do something almost magical: It could transform carbon dioxide into fuel using only the power of sunlight.

The promise is big: Take something we want less of in the air and turn it into useable energy, something we definitely want more of. But could it reverse climate change?

The news release doesn't shy away from calling the method a breakthrough. "It's very important that we develop these kinds of materials, these kinds of technologies, because accumulation of carbon dioxide is a big problem right now," senior author Fernando Uribe-Romo tells Inverse. "As we're starting to see all the effects of global warming being accentuated right now - like water rising, and coral reefs dying, and the bees dying - we need to do something about it."

Here's what Uribe-Romo and his research team did. They synthesized a type of material called a metal-organic framework, which is made from titanium and organic molecules that work as light-harvesting antennae to capture energy from visible light. The material that results organizes itself in a sort of nanoscopic honeycomb pattern that can be filled with carbon dioxide through diffusion. The input of blue light energy spurs a chemical reaction that breaks down the carbon dioxide into reduced forms, including formate and formamides. It's a sort of artificial photosynthesis, mimicking how plants transform air and sunlight into sugars that can be used as fuel.

Uribe-Romo envisions a world where something like this could be used in conjunction with power plants, scrubbing flue gas of carbon dioxide while producing a useful fuel. Or, perhaps, the material could be integrated into roof shingles, where they would remove CO2 passively while producing stored energy.

But it's unlikely that this technology or others like it will contribute significantly to reducing global dependence on fossil fuels, at least not in the near future.

"This is undoubtedly cool science," Ken Caldeira admits. Caldeira is an atmospheric scientist with Stanford University, and while he's not affiliated with the study, he's an expert on efforts to pull carbon out of the atmosphere to sidestep the worst consequences of climate change.

Caldeira isn't entirely sold on the premise of this. "I'm skeptical that this is really going to be the economic path forward, but gee whiz, if it could be, that would be really cool," he said.

Caldeira can come up with a lot of reasons why this vision of the future is unlikely. In order to become commonplace, this process would have to become a lot cheaper and a lot more efficient. It would have to outcompete other technologies for how to clean the air and power the world, including plants themselves. "One advantage of plants is that they are these self-assembling, self-reproducing robots," says Caldeira. "Are they going to be more cost-effective than plants at turning atmospheric CO2 into some kind of usable energy?"

Uribe-Romo's research falls into the broader category of solar fuels - any process by which energy from the sun is harnessed and chemically stored. Alternative fuels will likely be important in a post-fossil fuel world, because fuels are much better at storing energy than batteries, likely being required well into the future for things like airplane flights.

There are two major categories of solar fuel: You can harness solar energy to break down water and capture hydrogen fuel, or you can use it to break down carbon dioxide into carbon-based fuels. There are lots of methods out there for accomplishing these things, though none has proven successful enough to look like a marketable solution.

The solar fuel research community is divided on the question of where funding and attention should be concentrated. Some argue for focusing exclusively on making hydrogen fuel from water, since there are some basic problems with using carbon dioxide, namely that it exists in very low concentrations in the atmosphere.

But Nate Lewis, a top expert in solar fuel technology and development, tells Inverse he absolutely advocates for investment in a diversity of approaches to the problem - even those that don't seem terribly promising from where we sit today. "You shouldn't just swing for the grand slam home runs when you don't even have anybody on base."

Lewis's research team is working on approaches that start with water as well as CO2. They've already built a demonstration prototype of a solar hydrogen system that works, and is more efficient at converting sunlight to fuel than plants. But, the reaction isn't stable over long periods of time, wouldn't be easy to manufacture, and isn't cost effective to scale up.

As for Uribe-Romo's work, "It's a step that could be an interesting step forward," says Lewis. "It would need a lot of improvement on a lot of fronts to be a framework for actual solar fuels technology, but it's an interesting scientific accomplishment."

To get any solar fuel tech to the point where it's competitive with other energy technologies, it's going to take sustained incentives and commitments from governments and industry, Lewis says. Today, the political climate is uncertain and the investment systems aren't structured to support this sort of basic research and development with uncertain payoffs.

But risky investments today are essential to the great breakthrough of tomorrow that we never saw coming. Uribe-Romo's work may or may not be a step on the path in the right direction, and the only way to know for sure is to keep walking.

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Can Artificial Photosynthesis Reverse Climate Change?

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Florida researchers announced last week that they had synthesized a material that could do something almost magical: It could transform carbon dioxide into fuel using only the power of sunlight. The promise is big: Take something we want less of in the air and turn it into useable energy, something we definitely want more of.

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posted by Pearl

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COHEN ET AL., SCIENCE ADVANCES, 2017. The use of photosynthetic microorganisms to provide much needed oxygen to damaged heart tissue could be a feasible approach to treating heart attacks, say the authors of a study published today (June 14) in Science Advances. Their paper describes the injection of the cyanobacterium Synechococcus elongatus into ischemic heart muscles of live rats, where, in response to light exposure, the microbes produced oxygen and improved organ function.

"It's a very novel and clever application of an innate microbial property to a very serious medical problem that really is in need of innovative solutions," says Susan Erdman, a microbiologist and immunologist at MIT who was not involved with the research. "I thought it was amazing and I was very excited about it."

"Their concept is totally unique," says cardiac surgery professor Arnar Geirsson of Yale School of Medicine who also did not participate in the work. "They are definitely thinking outside the box."

Photosynthetic organisms capture energy from sunlight and use it to convert carbon dioxide and water into carbohydrates for growth. The process creates a surplus of oxygen, which the organisms simply expel into the atmosphere, much to the delight of aerobic organisms such as humans.

Not taking these basic facts of existence for granted, Joseph Woo, a cardiothoracic surgeon at Stanford University, saw them as a solution to a problem. "One day I was thinking: what is the fundamental problem with a heart attack? It's the absence of oxygen being delivered to the heart muscle.," he recalls. "And, what in nature makes oxygen for us every single minute? Plants."

"[Cardiologists] are always thinking about how to deliver more blood [to ischemic heart tissue]," Woo continues. But, if oxygen is the critical component, he thought, "what if you could take a plant, or the photosynthetic mechanism of a plant, and put it right next to a heart cell?"

To investigate this unusual idea, Woo's team took an equally unusual approach. "We started grinding up kale and spinach to isolate the chloroplasts and put them with heart cells," he says. But the results of these experiments were disappointing. "What we found is that chloroplasts do not like being outside of a plant cell," he says, "they're not very stable."

So, the team instead tried the photosynthetic unicellular microorganism S. elongatus. "We put them with heart cells in a dish and we found that they could live together and, when we shone light on them, they could produce oxygen," says Woo.

The team then tested the idea in live rats. They gave the animals heart attacks and then injected their hearts with S. elongatus and exposed the hearts to light. After just 10 minutes, oxygen in the bacteria-containing and light-exposed hearts had risen approximately 25-fold compared with just a 3-fold rise in oxygen in bacteria-containing hearts kept in darkness. And by 45 minutes, left ventricle pressure and cardiac output had improved, suggesting increased heart contractility.

STANFORD UNIVERSITY SCHOOL OF MEDICINE, DEPARTMENT OF CARDIOTHORACIC SURGERY The microbes also provided long-term improvements to heart function, the team showed. Four weeks after rats were subjected to temporary cardiac ischemia (60 minutes)-during which the animals were, or were not, injected with S. elongatus and exposed to light-analyses of heart function revealed that recipients of the microbe treatment had significantly improved contractility compared with controls.

Once injected, the bacteria remain detectable in the heart tissue for about a day, says Woo, but during that time they do not appear to cause any toxic effects or significant immune response. "It's almost like the body just ignored them," he says. Though, he adds, it is also possible that the bacteria are cleared by "a mechanism that we are not effectively assaying right now."

To examine bacterial clearance as well as determine the safety and potential feasibility of such a photosynthetic oxygen therapy "more detailed studies will be necessary," says Geirsson, and "any use of such a treatment for human diseases is a long way off." But, if it were to reach the clinic, he adds, "there are many diseases and conditions it could be applied to"-including strokes, peripheral tissue ischemia, and more.

It will certainly be "very exciting" to see where the technology goes, says Erdman. "One of the very fun things about science," she says, "is that sometimes there are these most fundamental of concepts, but they can be brilliantly tweaked to entirely novel ends, and this is just such an example."

J.E. Cohen et al., "An innovative biologic system for photon-powered myocardium in the ischemic heart," Science Advances, 3:e1603078, 2017.

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Bright Lights and Bacteria Treat Rats' Heart Attacks

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COHEN ET AL., SCIENCE ADVANCES, 2017. The use of photosynthetic microorganisms to provide much needed oxygen to damaged heart tissue could be a feasible approach to treating heart attacks, say the authors of a study published today (June 14) in Science Advances.

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http://phoebethephoton.blogspot.com/

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Plants watering their own roots... Interesting?

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The cloud forests of Brazil, by R. Oliviera, one of the plant scientists behind this new research

How does water travel through a plant? Your answer's probably a simple one. Water moves from the soil, up through the roots and stems of a plant, through the leaves and out into the surrounding atmosphere.

But recent research has shown that our traditional understanding of the movement of water through plants is incomplete. Under certain specialised conditions, some plants have evolved the ability to absorb water through their leaves, move it down the xylem, and them release it into the soil. The plants are actually watering their own roots - and their own seedlings. This off-beat mechanism for water uptake works well enough that these plants can continue to photosynthesise and grow, even when the soil they are growing in are dry.

The trees the researchers studied - Drimys brasiliensis - grow in the cloud forests of Brazil, where the trees are almost constantly covered in fog. The atmosphere around the leaves has a higher water potential than the leaves themselves, allowing foliar water uptake. The exact pathway for water entry is still under discussion: this particular species has a hydrophilic cuticle that could facilitate water entry, as well as hydrophilic tissues within the leaf that could provide water storage.

At least 70 species, across seven different ecosystems, have been identified as using this 'back-to-front' water transport mechanism, pulling water out of the sky and down to the rhizosphere.

These new findings have important implications for our existing models of the climate and our ecosystems, which often consider soil water as the only source of water for plants.

It's another example of how plants are constantly over-turning our expectations.

Eller, C. B., Lima, A. L. and Oliveira, R. S. (2013), Foliar uptake of fog water and transport belowground alleviates drought effects in the cloud forest tree species, Drimys brasiliensis (Winteraceae). New Phytologist, 199: 151-162. doi: 10.1111/nph.12248

Read a full open access commentary in the New Phytologist

Read the abstract of the original article in the New Phytologist

Read a blog post on this article in the Annals of Botany blog.

Read a blog post on this article in the New Phytologist blog.

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The cloud forests of Brazil, by R. Oliviera, one of the plant scientists behind this new research How does water travel through a plant? Your answer's probably a simple one. Water moves from the soil, up through the roots and stems of a plant, through the leaves and out into the surrounding atmosphere.

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Wider reading for interviews and personal statements below:

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Wider reading for interviews and personal statements below:

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https://thebiologist.rsb.org.uk/biologist

https://www.nationalgeographic.com/science/

https://www.newscientist.com/

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Post below if you find any other such events

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There was almost something biblical about the scene of devastation that lay before Richard Kock as he stood in the wilderness of the Kazakhstan steppe. Dotted across the grassy plain, as far as the eye could see, were the corpses of thousands upon thousands of saiga antelopes. All appeared to have fallen where they were feeding.

Some were mothers that had travelled to this remote wilderness for the annual calving season, while others were their offspring, just a few days old. Each had died in just a few hours from blood poisoning. In the 30C heat of a May day, the air around each of the rotting hulks was thick with flies.

The same grisly story has been replayed throughout Kazakhstan. In this springtime massacre, an estimated 200,000 critically endangered saiga - around 60% of the world's population - died. "All the carcasses in this one of many killing zones were spread evenly over 20 sq km," says Kock, professor of wildlife health and emerging diseases at the Royal Veterinary College in London. "The pattern was strange. They were either grazing normally with their newborn calves or dying where they stood, as if a switch had been turned on. I've never seen anything like that."

The saiga - whose migrations form one of the great wildlife spectacles - were victims of a mass mortality event (MME), a single, catastrophic incident that wipes out vast numbers of a species in a short period of time. MMEs are among the most extreme events of nature. They affect starfish, bats, coral reefs and sardines. They can push species to the brink of extinction, or throw a spanner into the complex web of life in an ecosystem. And according to some scientists, MMEs are on the rise and likely to become more common because of climate change.

The MME that has pushed the saiga closer to extinction struck in 2015. Kock was part of an international team studying the animals as they gathered for the calving season. For most of the year, saiga are on the move, able to avoid predatory wolves and human poachers by sprinting at more than 40mph, making them one of the fastest ungulates, or hoofed animals. But once a year they put their migration on pause to calve in vast groups when the grass is at its lushest, before it is scorched by the sun.

In 2015, the main gathering in the Betpak-Dala region of central Kazakhstan, an area roughly the size of the British Isles, numbered 250,000. Nearby, other groups were thousands strong. Saiga are remarkable animals. Their bulbous noses, which hang over their mouths, give these antelopes an almost comical appearance. The nose is flexible and can be inflated, helping them to breathe warm air in the freezing winters and filter air in the arid summers as they sprint with their heads down in a cloud of dust. The species has been hit by mass die-offs before. In 1981, around 70,000 died suddenly in a few days, while in 1988 another 200,000 died. The creatures are also victims of poachers.

These reports of mass mortality events are probably underestimates in terms of occurrence and sheer magnitude

Adam Siepielski

"In 2014, we believed there were about 250,000 adults and they produced a good number of calves - perhaps a couple of hundred thousand. It looked a viable population and we'd expected a population of a million soon. There was even talk of them coming off the critically endangered list," Kock says.

But as the scientists watched a year later, the mothers fell sick and began to drop dead. "It wasn't as if the disease started at one end and spread - there was no time for transmission of the pathogen from animal to animal. It was too quick," he says. "Within two or three days, everything was dying. By the end of the week, every single one was dead."

The scientists on the ground pinpointed blood poisoning as the cause, but were puzzled as to why whole herds were dying so quickly. After 32 postmortems, they concluded the culprit was the bacterium Pasteurella multocida, which they believe normally lives harmlessly in the tonsils of some, if not all, of the antelopes. In a research paper published in January in Science Advances, Kock and colleagues contrasted the 2015 MME with the two from the 1980s. They concluded that a rise in temperature to 37C and an increase in humidity above 80% in the previous few days had stimulated the bacteria to pass into the bloodstream where it caused haemorrhagic septicaemia, or blood poisoning.

The weather link raises the spectre of climate change. Just as it is rarely wise to link a single extreme weather event - whether it's the Australian heatwave, last summer's Hurricane Harvey or this winter's North American cold snap - to climate change, it is equally difficult to blame an MME on global warming. But what can be said with confidence is that the sorts of extreme weather events linked to MMEs - such as the temperature and humidity rise that nearly wiped out the saiga - will become more frequent.

Australians know all about extreme weather. While much of Europe and North America has endured a bitter start to the year, the Australian summer has been a scorcher. In January, temperatures in Sydney topped 47C, the city's highest since 1939. The toll on wildlife has been devastating. As the mercury rose, corpses of critically endangered flying foxes - or fruit bats - began to pile up under the trees in New South Wales. Horrified wildlife campaigners at one colony in Campbelltown, south of Sydney, discovered 400 dead bats. Some were still hanging from trees. Many were babies, abandoned by their parents in their own desperate search for shade.

Flying foxes are well adapted to normal Australian summers. But above 40C, they are unable to regulate their body temperature and can die from overheating. This year's deaths were grim enough, but they were dwarfed by the MME of 2014, when at least 45,000 flying foxes were killed on one hot day in south-east Queensland. Some colonies had more dead bodies than living bats. Their corpses were piled thick on the ground as the three species there - the black, little red and grey-headed - were hit.

Events like the disaster that struck the flying foxes and saiga appear to be growing in number. The most thorough study of its kind published in the Proceedings of the National Academy of Sciences in 2015 uncovered 727 accounts of MMEs involving 2,407 animal populations since 1940. It found that not only are reports of MMEs on the increase - by about one event a year - but the number of animals killed in each event is on the rise for birds, fish and marine invertebrates.

Adam Siepielski, an evolutionary ecologist at the University of Arkansas and a co-author of the paper, became fascinated by the phenomena after hearing a radio report of millions of sardines and anchovies dying. "These reports of MMEs are probably underestimates in terms of occurrence and sheer magnitude," he says. "There is additionally a challenge in trying to understand whether this increased occurrence is a real event, or whether there are more people observing these things and [they are] more likely to report them. We call this the epidemic of awareness."

The study found that disease was the biggest factor in MMEs, playing a role in a quarter of them. Around 19% were directly linked to human behaviour such as pollution. Factors linked directly to climate - including extremes of hot and cold, oxygen stress and starvation - collectively contributed to about a quarter.

Untangling the causes - and working out the role of climate change in MMEs is difficult. "In many cases, there are multiple stressors - such as, in the case of the saiga, a low-lying bacterial infection, slightly higher humidity and higher temperatures," says Siepielski.

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Flying foxes - also known as fruit bats. In 2014, at least 45,000 of them died in one day from overheating in Queensland, Australia. Photograph: Reuters

"There are some mass mortality events linked directly to extreme heatwaves or cold snaps. In other cases there could be indirect changes, where shifts in temperature cause diseases to be more common and which lead to an MME."

That kind of temperature-related outbreak is now thought to lie behind one of the biggest die-offs ever observed in the natural world, in which hundreds of millions of starfish off the west coast of America began to "melt" into white gloop. More than 20 species of starfish along the coast from Mexico to Alaska were hit by the sea star wasting disease, a condition caused by a parvovirus - the group of viruses that cause gastrointestinal problems in animals. The virus left the starfish vulnerable to bacterial infection. Within one or two weeks of infection, white cuts appeared on their bodies and the creatures became listless. Some ripped off their infected arms and tried to walk away. But for most the disease was deadly. Like the bacteria that triggered the MME in saiga, the virus appears to have been present in starfish for decades - if not longer. Samples stored in museums since the 1940s tested positive.

An MME can push a species closer to extinction. But it can also have knock-on effects elsewhere in the fragile food web. In tidal pools on the west coast, where once there was a healthy mix of species, mussels - food for starfish - are starting to dominate. Off California, another source of starfish food, sea urchins, are also on the rise - causing a fall in the availability of kelp, the sea urchins' main food source. That decline could hit species that depend on it for shelter, food and protection.

A paper published last year in the Philosophical Transactions of the Royal Society concluded that the die-off was probably linked to warmer seas. The team, led by Morgan Eisenlord at Cornell University, looked at the links between ocean temperatures and disease in the most common species on the west coast, the ochre sea star, as well as testing the effects of warmer water in the lab. Warmer than usual water didn't just put the starfish under stress, it also made infectious agents more prevalent, they concluded.

Kock is confident that climate change will lead to more MMEs - pushing vulnerable species closer to extinction and altering the food web. He believes that conservationists should be on the lookout for other mortality events in species such as reindeer and elk. "The tragedy is, we will probably see more events like the event that affected the saiga," he says. "Evolution takes millions of years and if we have a shift in environmental conditions, everything that's evolved in that particular environment is under different pressures. Microbes adapt and can respond to changes quickly, but mammals take hundreds of thousands of years or millions of years to adapt. That's the real worry."
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