Roll over eggs…it’s time for (unrolled) tobacco leaves

Tobacco leaf infected with Tobacco Mosaic Virus. Courtesy of Clemson University - USDA Cooperative Extension Slide Series

Timeline, 2008: If you’ve ever been asked about allergy to egg products before receiving a flu vaccine, you have had a little encounter with the facts of vaccine making. Flu viruses to produce the vaccine are painstakingly grown in chicken eggs because eggs make perfect little incubators for the bugs.

So…many…eggs

There are problems—in addition to the allergy issue—that arise with this approach. First of all, growing viruses for a million vaccine doses usually means using a million fertilized, 11-day-old eggs. For the entire population of the United States, 300 million eggs would be required. Second, the process requires months of preparation, meaning a slow turnaround time for vaccines against a fast-moving, fast-changing disease. Last, if there is anything wrong with the eggs themselves, such as contamination, the whole process is a waste and crucial vaccines are lost.

The day may come when we can forget about eggs and turn to leaves. Plants can contract viral disease just like animals do. In fact, an oft-used virus in some research fields is the tobacco mosaic virus, which, as its name implies, infects tobacco plants. It gives a patchy look to the leaves of infected plants, and researchers use this feature to determine whether the virus has taken hold.

Bitter little avatars of evil used for good?

Tobacco plants themselves, bitter little avatars of evil for their role in the health-related effects of smoking, serve a useful purpose in genetic research and have now enhanced their approval ratings for their potential in vaccine production. Plants have caught the eye of vaccine researchers for quite a while because they’re cheaper and easier to work with than animal incubators. Using plants for quick-turnaround vaccine production has been a goal, but a few problems have hindered progress.

To use a plant to make a protein to make a vaccine, researchers must first get the gene for the protein into the plant. Previous techniques involved tedious and time-consuming processes for inserting the gene into the plant genome. Then, clock ticking, there was the wait for the plant to grow and make the protein. Add in the Byzantine process of obtaining federal approval to use a genetically modified plant, and you’ve got the opposite of “rapid” on your hands.

One solution to this problem would simply be to get the gene into the plant cell cytoplasm for immediate use. It’s possible but involves meticulously injecting a solution with the gene sequence into each leaf. Once the gene solution is in, the plant will transcribe it—copy it into mRNA—in the cell cytoplasm and then build the desired protein based on the mRNA code. But there has been no way to take hand injection to the large-scale production of proteins, including for vaccines.

Age-old vacuum suction =  high-tech high-throughput

To solve this problem, researchers turned to one of our oldest technologies: vacuum suction. They grew tobacco plants to maturity and then clipped off the leaves, which they submerged in a solution. The solution was spiked with a nasty bug, Agrobacterium tumefaciens, a pathogen responsible for the growth of galls, or tumors, on plants. Anyone working in agriculture fears this bacterium, a known destroyer of grapes, pitted fruit trees, and nut trees. But it does have one useful feature for this kind of work: It can insert bits of its DNA into plant cells. The researchers tricked A. tumefaciens into inserting another bit of DNA instead, the code for the protein they wanted to make.

To get the solution close to the cells, the investigators had to get past air bubbles, and that’s where the vacuum came in. They placed the submerged leaves into a vacuum chamber and flipped a switch, and the activated chamber sucked all the air out of the leaves. When the vacuum was turned off, the solution flowed into the now-empty chambers of the leaf, allowing the A. tumefaciens-spiked solution to bathe the plant cells. After 4 days and a few basic protein-extraction steps, the research team had its protein batch. According to the team lead, “any protein” could be made using this process, opening up almost unlimited possibilities and applications for this approach.

Vaccines…or combating bioterrorism?

The technology has come far enough that a US company has taken steps toward manufacturing vaccines using tobacco leaves.  And it appears that the applications go beyond vaccines, as one news story has noted…the tobacco plants might also be used to produce antidotes to common agents of bioterrorism.

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The cooperative, semi-suicidal blob lurking beneath the cow pasture

Aggregating Dictyostelium discoideum; photo from a series available at Wikimedia Commons

Amoebae gone to pasture

Timeline, 2009: Lurking beneath the soil and cow patties of a southeast Texas cow pasture, the cellular slime mold cloned itself and cloned itself again until it was about 40 feet across, billions of cells dense. The thing is, this enormous creature was really neither a slime nor a mold, but a group of social microbes, amoebas that were all exactly identical to one another.

It’s a cell, it’s a colony, it’s…a multicellular organism!

No one is quite sure why some microbes are social. But the cellular slime mold, Dictyostelium discoideum, makes a great model for figuring out why. This organism, a eukaryote, can start out life as a single cell, one that hangs out waiting for a hapless bacterium to wander by so it can have dinner. But if bacteria are in short supply or the soil dries up, slime molds can do some marvelous things. They can start socializing with each other, forming colonies—apparently quite large colonies. But they also can shift from being single-celled organisms or single-celled colonial organisms to becoming a multicellular organism. In the really bad times, these cells can signal to one another to differentiate into two different tissues, officially becoming multicellular.

In addition, these brainless blobs also exhibit altruism, a kind known as suicidal altruism in which some cells in a colony commit cell suicide so that cells elsewhere in the colony can thrive. And as the discovery in the Texas cow pasture shows, the organisms can exist in enormous clonal colonies, a quivering gelatinous mass just under the soil, waiting for conditions to improve.

An affinity for dung

How did the researchers even find this slime mold? They had to get themselves into the “mind” of the slime mold and figure out where this species might be most prone to going clonal, a response to an uninviting environment. Given that slime molds are fond of deep, humid forests, the researchers opted to search for the clonal variety in a dry-ish, open pasture at the edge of such forests. Why would they even expect D. discoideum to be there? Because the amoebae also happen to have an affinity for dung, as well as soil.

After careful sampling from 18 local fields, which involved inserting straws into cow patties and surrounding soil, the research team tested their samples for the presence of amoebae. Once the dishes showed evidence of the slime mold, the investigators then sampled each group and sequenced the genome. That’s when they realized that 40 feet of one cow pasture was one solid mass of amoebae clones.

The winner clones it all?

These findings raise intriguing questions for microbial ecologists. One problem they’re tackling is what determines which clone gets to reproduce so wildly at the edges of acceptable amoeba territory. Is it just one clone that arrives and gets to work, or do several show up, have a competition, and the winner clones all? They tested this idea in the lab and found that none of the clones they tested seemed to have any particular competitive advantage, so the selection process for which amoeba gets to clone at the edges remains a mystery.

Another question that intrigues the ecologists is why these single-celled organisms cooperate with one another in the first place. Such clonal existence is not unknown in nature—aspen trees do it, and so do sea anemones. And researchers have identified as many as 100 genes that seem to be associated with cooperative behavior in the slime mold. One explanation for cooperating even to the extreme of individual suicide is the clonal nature of the colony: the more identical the genes, the more the species derives from sacrificing for other members of the species. They ensure that the same genes survive, just in a different individual.

Machiavellian amoebae: cheaters among the altruists

Not all amoebae are altruistic, and some apparently can be quite Machiavellian. Some individual amoeba carry cooperation genes that have undergone mutations, leading them to be the cheaters among the altruists and take advantage of the altruistic suicide to further their own survival. What remains unclear is why cooperation continues to be the advantageous route, while the mutant cheats keep getting winnowed out.

Amoebae gone to pasture

By Emily Willingham

Word count: 672

 

Lurking beneath the soil and cow patties of a southeast Texas cow pasture, the cellular slime mold cloned itself and cloned itself again until it was about 40 feet across, billions of cells dense. The thing is, this enormous creature was really neither a slime nor a mold, but a group of social microbes, amoebas that were all exactly identical to one another.

No one is quite sure why some microbes are social. But the cellular slime mold, Dictyostelium discoideum, makes a great model for figuring out why. This organism, a eukaryote, can start out life as a single cell, one that hangs out waiting for a hapless bacterium to wander by so it can have dinner. But if bacteria are in short supply or the soil dries up, slime molds can do some marvelous things. They can start socializing with each other, forming colonies—apparently quite large colonies. But they also can shift from being single-celled organisms or single-celled colonial organisms to becoming a multicellular organism. In the really bad times, these cells can signal to one another to differentiate into two different tissues, officially becoming multicellular.

In addition, these brainless blobs also exhibit altruism, a kind known as suicidal altruism in which some cells in a colony commit cell suicide so that cells elsewhere in the colony can thrive. And as the discovery in the Texas cow pasture shows, the organisms can exist in enormous clonal colonies, a quivering gelatinous mass just under the soil, waiting for conditions to improve.

How did the researchers even find this slime mold? They had to get themselves into the “mind” of the slime mold and figure out where this species might be most prone to going clonal, a response to an uninviting environment. Given that slime molds are fond of deep, humid forests, the researchers opted to search for the clonal variety in a dry-ish, open pasture at the edge of such forests. Why would they even expect D. discoideum to be there? Because the amoebae also happen to have an affinity for dung, as well as soil.

After careful sampling from 18 local fields, which involved inserting straws into cow patties and surrounding soil, the research team tested their samples for the presence of amoebae. Once the dishes showed evidence of the slime mold, the investigators then sampled each group and sequenced the genome. That’s when they realized that 40 feet of one cow pasture was one solid mass of amoebae clones.

These findings raise intriguing questions for microbial ecologists. One problem they’re tackling is what determines which clone gets to reproduce so wildly at the edges of acceptable amoeba territory. Is it just one clone that arrives and gets to work, or do several show up, have a competition, and the winner clones all? They tested this idea in the lab and found that none of the clones they tested seemed to have any particular competitive advantage, so the selection process for which amoeba gets to clone at the edges remains a mystery.

Another question that intrigues the ecologists is why these single-celled organisms cooperate with one another in the first place. Such clonal existence is not unknown in nature—aspen trees do it, and so do sea anemones. And researchers have identified as many as 100 genes that seem to be associated with cooperative behavior in the slime mold. One explanation for cooperating even to the extreme of individual suicide is the clonal nature of the colony: the more identical the genes, the more the species derives from sacrificing for other members of the species. They ensure that the same genes survive, just in a different individual.

Not all amoebae are altruistic, and some apparently can be quite Machiavellian. Some individual amoeba carry cooperation genes that have undergone mutations, leading them to be the cheaters among the altruists and take advantage of the altruistic suicide to further their own survival. What remains unclear is why cooperation continues to be the advantageous route, while the mutant cheats keep getting winnowed out.

Microbes redirect our best-laid plans

Greeks at War (pottery from the British Museum; photo courtesy of Wikimedia Commons)

The madness of King George

Timeline, 2006: It’s not that unusual for disease to alter the course of history–or, history as humans intended it to be. Some scholars believe, for example, that the intransigence of King George III of England arose from his affliction with porphyria, a heritable metabolic disorder that can manifest as a mental problem, with symptoms that include irrational intractability. But it’s rarer for a disease to shift the balance of power so entirely that one nation gains the upper hand over another. Yet that appears to be what happened to the city-state of Athens just before the Peloponnesian Wars of around 430 B.C. The upshot of the wave of disease and the wars was that Sparta conquered Athens in 404 B.C.

Spartans had a little microbial assistance

Sparta may have owed its big win to a small bacterium, Salmonella enterica enterica serovar Typhi, the microbe responsible for typhoid fever. A plague swept across Athens from 430 to 426 B.C., having traveled from Ethiopia to Egypt and Libya before alighting in the Greek city and destroying up to a third of its population. In addition, it brought to a close what became known as the Golden Age of Pericles, a time when Athens produced some of its most amazing and widely recognized art, artists, and philosophers, including Aeschylus, Socrates, the Parthenon, and Sophocles. Pericles was a statesman who oversaw the rebuilding of Athens following the Greek win in the Persian Wars, and he guided the city-state to a more democratic form of rule and away from the dictatorships of the previous regimes. In the process, the city flourished in art and architecture.

And then along came the plague. The Greek historian Thucydides, who chronicled the Peloponnesian Wars, left behind such a detailed account of the plague, its symptoms, and what happened to its victims, that intrigued medical detectives have ever since debated about what might have caused it. Thucydides, himself a plague survivor, vividly described the sudden fever, redness of the eyes, hemorrhaging, painful chest and cough, stomach distress, and diarrhea that ultimately led to death in so many cases. He also mentioned pustules and ulcers of the skin and the loss of toes and fingers in survivors. This litany of symptoms produced many candidate causes, including bubonic plague, anthrax, smallpox, measles, and typhoid fever.

Construction crews yet again uncover something interesting

In the mid-1980s, a construction crew was busy digging a hole for a subway station in the city of Kerameikos when they uncovered a mass burial site. Unlike other Greek burial sites, this one bore marks of hasty and haphazard burials, and the few artefacts that accompanied the bones dated it to the time of the plague that destroyed Athens. Researchers were able to harvest some teeth from the site and analyze the tooth pulp, which retains a history of the infections a person has suffered. They examined DNA sequences from the pulp for matches with suggested microbial agents of the plague, and finally found a match with the typhoid bacterium.

Typhoid Mary: Intent on cooking, ended up killing

One discrepancy between the disease pattern of typhoid fever and that described by Thucydides is the rapidity of onset the Greek historian detailed. Today, typhoid fever, which still infects millions of people worldwide, takes longer to develop in an infected individual, and sometimes never develops at all. People who bear the virus but don’t become ill themselves are “carriers.”

Perhaps the most famous carrier was Typhoid Mary, Mary Mallon, a cook in New York City at the beginning of the 20th century. It is believed that she infected hundreds of people, with about 50 known cases and a handful of deaths being directly associated with her. Typhoid Mary was told not to work as a cook any longer or she would be quarantined, but she simply disappeared for awhile and then turned up under a different name, still working as a cook. After another outbreak was traced to her, she was kept in quarantine for 23 years until she died.

Is the tree of life really a ring?

A proposed ring of life

The tree of life is really a ring

When Darwin proposed his ideas about how new species arise, he produced a metaphor that we still adhere to today to explain the branching patterns of speciation: The Tree of Life. This metaphor for the way one species may branch from another through changes in allele frequencies over time is so powerful and of such long standing that many large studies of the speciation process and of life’s origins carry its name.

It may be time for a name change. In 2004, an astrobiologist and molecular biologist from UCLA found that a ring metaphor may better describe the advent of earliest eukaryotes. Astrobiologists study the origins of life on our planet because of the potential links between these earthly findings and life on other planets. Molecular biologists can be involved in studying the evolutionary patterns and relationships that our molecules—such as DNA or proteins—reveal. Molecular biologist James Lake and astrobiologist Mary Rivera of UCLA teamed up to examine how genomic studies might reveal some clues about the origins of eukaryotes on Earth.

Vertical transfer is so 20th century

We’ve heard of the tree of life, in which one organism begets another, passing on its genes in a vertical fashion, with this vertical transfer of genes producing a tree, with each new production becoming a new branch. The method of gene transfer that would produce a genuine circle, or ring, is horizontal transfer, in which two organisms fuse genomes to produce a new organism. The ends of the branches in this scenario fuse together via their genomes to close the circle. It is this fusion of two genomes that may have produced the eukaryotes.

Here, have some genes

Eukaryotes are cells with true nuclei, like the cells of our bodies. The simplest eukaryotes are the single-celled variety, like yeasts. Before eukaryotes arose, single-celled organisms without nuclei—called prokaryotes—ruled the Earth. We lumped them together in a single kingdom until comparatively recently, when taxonomists broke them into two separate domains, the Archaebacteria and the Eubacteria, with the eukaryotes making up a third. Archaebacteria are prokaryotes with a penchant for difficult living conditions, such as boiling-hot water. Eubacteria include today’s familiar representatives, Escherichia coli.

Genomic fusion

According to the findings of Lake and Rivera, the two prokaryotic domains may have fused genomes to produce the first representatives of the Eukarya domain. By analyzing complex algorithms of genomic relationships among 30 organisms—hailing from each of the three domains—Lake and Rivera produced various family “trees” of life on Earth, and found that the “trees” with the highest cumulative probabilities of having actually occurred really joined in a ring, or a fusion of two prokaryotic branches to form the eukaryotes. Recent research If we did that, the equivalent would be something like walking up to a grizzly bear and hand over some of your genes for it to incorporate. Being eukaryotes, that’s not something we do.

Our bacterial parentage: the union of Archaea and Eubacteria

Although not everyone buys into the “ring of life” concept, their findings help resolve some confusion over the origins of eukaryotes. When we first began analyzing the relationship of nucleated cells to prokaryotes, we identified a number of genes—that we call “informational” genes—that seemed to be directly inherited from the Archaea branch of the Tree of Life. Informational genes are involved in the processes like transcription and translation, and indeed, recent “ring of life” research suggests a greater role for Archaea. But we also found that many eukaryotic genes traced back to the Eubacteria domain, and that these genes were more organizational in nature, being involved in cell metabolism or lipid synthesis.

Applying the tree metaphor did not help resolve this confusion. If eukaryotes vertically inherited these genes from their prokaryotic ancestors, we would expect to see only genes representative of one domain or the other in eukaryotes. But we see both domains represented in the genes, and the best explanation is that organisms from each domain fused entire genomes—horizontally transferring genes—to produce a brand new organism, the progenitor of all eukaryotes: yeasts, trees, giraffes, killer whales, mice, … and us.

Did we find life on Mars–and kill it?

Did we kill life on Mars?

The movie War of the Worlds may have it wrong. The collision between life forms from different planets may not involve fire, mutual bloody conflict, and pathogen exchange. Instead, it may already have happened, ending simply, quietly, and unilaterally, in water and heat at the microscopic level.

In the 1970s, we sent two Viking space probes to Mars on a mission to test for life on the red planet. The prevailing dogma among scientists was that water was required for life, anywhere in the universe. This viewpoint has evolved since then as we’ve discovered some Earthbound organisms, including the microbe Acetobacter peroxidans, relying on very different, non-water-based mechanisms for survival.

Organisms living alternative lifestyles

These discoveries of organisms living alternative lifestyles here at home led to the formation of the “weird life” panel, a U.S. group that addresses concerns that we may be too Earth-centric as we search for life beyond our planet. This narrow view may have led to a terrible accident on our Viking visits: we may have encountered Martian life and then drowned or baked it to death.

The Viking probes performed a series of experiments on samples from the Martian surface. The labeled release experiment involved exposing Martian soil samples to water and a nutrient source with incorporated radiolabeled carbon. To everyone’s excitement, the exposure elicited a spike in radiolabeled carbon dioxide (CO2), meaning that the nutrient source could have been metabolized, the carbon incorporated with oxygen to make CO2. However, the experiment seemed to fizzle as the CO2 levels dropped and plateaued.

Evidence of life–and death?

In the pyrolytic release experiments, radiolabeled CO2 appeared to have been incorporated into organic molecules by something in the Martian soil. This type of experiment would reflect activity similar to photosynthesis, which grabs CO2 from the air and incorporates it into the organic macromolecule glucose. In this Martian test, four of the seven soil samples showed significant production of organic molecules that had incorporated the radiolabeled carbon from the CO2. Interestingly, the sample treated with liquid water produced even less organic product than the control. In addition, the Viking probes found evidence of chemical oxidation (oxygen breaking down macromolecules), but we found no oxidative activity in the Martian soil on subsequent analyses.

The results seemed disappointing—they at first held promise for a life form metabolizing and catabolizing molecules. But as each experiment fizzled, expectations diminished, and everyone assumed that there was simply no life on Mars.

Oops

A review of the data from a different, less Earth-centric perspective, however, results in a potential confirmation of life on Mars. The scientists who devised this story point out that Mars is conducive to life based on hydrogen peroxide (HP). For example, the higher the HP content, the lower the freezing point of an aqueous HP solution. Even at freezing, HP does not form cell-destroying crystals, as water does. An HP also pulls water vapor from the air, an efficient way to grab water in a dry place like Mars.

Exposing an HP-based cell to water would drown it, and applying heat to the soil would bake it. These two things are exactly what the Viking probes did to Martian soil samples in executing the experiments. If HP-based life forms were present, they would have produced results exactly like those the probes found. For example, they could have taken the radiolabeled macromolecules and metabolized them, releasing CO2, but eventually dying as the water added to the samples overwhelmed them. Every single outcome of the Viking experiments appears to be consistent with a hypothesis that there might have been HP-based life on Mars.

We’ve now sent a new probe, the Phoenix, to the red planet. Data from the probe don’t answer all questions but do indicate the presence of “organics” on Mars. The next step is the Mars Science Laboratory, expected to launch next year with a Mars ETA in 2012. Will it settle the Life on Mars question once and for all?

Crazy cat lady may have microbe to blame

Toxoplasma gondii is the cat-borne parasite responsible for causing toxoplasmosis and a host of other problems in humans. This close relative of the malaria-causing protozoan may drive human behavior and immunity, in addition to causing acute illness and devastating birth defects. Recent research points to a single gene underlying this parasite’s virulence in the human host. It’s scary yet fascinating to think that a single gene from a single organism could have such dramatic effects on our species.

Warning pregnant women away from litter boxes

Because T. gondii infection can result in serious fetal defects, many pregnant women have heard of toxoplasmosis, an illness that often goes unnoticed in the afflicted person. Pregnant women are warned away from cat litter boxes and even away from gardening because contact with cat feces can mean contact with the parasite. T. gondii spends the sexual part of its life cycle in cats, but for its asexual life, it can parasitize a number of hosts, from pigs to lambs to mice to people. People also can acquire the infection from eating undercooked meat or drinking contaminated water. In some countries, like Brazil, up to 60% of the population has been exposed to T. gondii; in the United States, about 33% of people tested have antibodies to the parasite, indicating past infection.

Link between parasite and schizophrenia

The “crazy cat lady” has practically become a social stereotype in the United States and other countries, conjuring the image of a woman who lives with 25 cats and talks to herself a lot. But researchers investigating schizophrenia have actually identified a potential link between people who are exposed to Toxoplasma infection and the manifestations of schizophrenia; for example, several studies have identified higher levels of antibodies to the parasite in people with schizophrenia, and infection with Toxoplasma can cause damage to brain cells that is similar to the damage seen in patients with schizophrenia. Toxoplasmosis can also sometimes lead to symptoms of psychosis.

The fact is that most people don’t know they have toxoplasmosis because they have healthy immune systems. In people with compromised immunity, however, such as those with HIV, T. gondii can precipitate an extreme form of dementia that eventually kills them. The dementia is so severe that the sufferer eventually becomes completely unaware of his or her surroundings and lapses into a coma. The bug, however, also can affect the central nervous system in healthy people and is also linked to severe eye problems even in patients who are not immunocompromised. One researcher has claimed that infection with the parasite makes men dumber and women act like “sex kittens.”

ROP18: Watch out for this one

There are different strains of T. gondii, and investigators have noted that the Type 1 strain is most closely associated with disease. Studies of T. gondii, which has a genome with about 6000 genes, have pinpointed the virulence capacity of the strain to a single gene, dubbed ROP18. This gene encodes a kinase, one of a huge class of cell signaling proteins that add phosphates to molecules. Typically in cell signaling, kinases exist in a series, phosphorylating the next protein in the pathway, which helps maintain regulation of the signaling. The most virulent T. gondii strains have a form of the gene that differs from that carried by benign strains. Researchers speculate that this kinase interferes with a cell’s normal signaling, hijacking it for its own purposes, including growth and reproduction. The good news is that because kinases are so important in cell signaling, pharmaceutical companies have developed libraries of molecules that inhibit specific kinases, so one potential path to preventing toxoplasmosis is to discover an inhibitor of ROP18.

Rats get a little nutty from it, too

Not only has this parasite been linked to the ability to alter human behavior, but it also appears to alter rodent behavior in ways that favor its own reproduction. For example, rodents exposed to toxoplasma via cat feces actually become more likely to hang out near cat urine. If a cat eats the infected animal, the toxoplasmosis bug can then move into the sexual phase of its life cycle in the cat.

Magnetic fields and the Q

Sorry, not for Trekkies. This Q is chemical.

People have been concerned for years about magnetic fields having adverse health effects–or even have peddled magnets as being health beneficial. But although scientists have demonstrated repeatedly a chemical response to magnetic fields, no one has ever shown the magnetic fields directly affecting an organism.

The earth’s core is weakly magnetic, the result of the attraction between electric currents moving in the same direction. Nature presents plenty of examples of animals that appear to use magnetic fields. Some bacteria can detect the fields and use them for movement. Birds appear to use magnetic fields to navigate, and researchers have shown that attaching magnets to birds interferes with their ability to navigate. Honey bees become confused in their dances when the earth’s magnetic fields fluctuate, and even amphibians appear to use magnetism for navigation. But no one has clearly demonstrated the mechanism by which animals sense and use magnetic fields.

Do pigeons use a compass?

Some research points to birds using tiny magnetic particles in their beaks to fly the right way. But these particles don’t tell the birds which way is north; they simply help the bird create a topographical map in its head of the earth over which it flies. The magnetic particles tell a pigeon there’s a mountain below, but not that the mountain is to the north. The conundrum has been to figure out how the pigeon knows which way is north in the absence of other pointers, such as constellations.

The answer to the conundrum lies with the bacteria. Scientists in the UK have used the purple bacterium Rhodobacter sphaeroides to examine what magnetic fields do at the molecular level. These bacteria are photosynthetic, and absorb light to convert to energy in the same way plants do. The absorbed light triggers a set of reactions that carry energy via electrons to the reaction center, where a pigment traps it. Under normal conditions, as the pigment traps the energy, it also almost instantaneously converts it to a stable, safe form, but sometimes the energy can form an excited molecule that can be biologically dangerous. As it turns out, these reactive molecules may be sensitive to magnetic fields.

A radical pair…or dangerous triplet

A chemical mechanism called the “Radical Pair Mechanism” is the method by which the potentially dangerous molecules can form. In this mechanism, an electron in an excited state may pair with another type of electron in an excited state. If the two excited molecules come together, they can form what is called a “radical pair in a singlet state,” because they are two singlets that have paired. Under normal conditions, this pairing does not happen; in the photosynthetic bacterium, for example, a compound called a quinone (Q) inhibits formation of this pair or of an equally damaging triplet of one electron type or the other.

But when a Q is not present, the singlet or triplet state results. If the triplet forms, it can interact with oxygen to produce a highly reactive, biologically damaging singlet molecule that we know as a “radical.” You have probably heard of radicals in the context of antioxidants—they are the molecules that antioxidants soak up to prevent their causing harm. You may also have heard of carotenoid, a pigment that is an antioxidant. In a normal photosynthetic bacterium, the carotenoids present serve as the Q, the compound that prevents formation of the damaging radical.

A helpful effect of magnetic fields?

Where do magnetic fields come in? Previous work indicated an influence of magnetic fields on triplet formation, and thus, on radical formation. One excellent model to test the effects of fields in a biological system is to remove the Q, the molecular sponge for the triplets, and then apply magnetic fields to see whether triplets—and radicals—form.

That’s exactly what the researchers did, using a mutated form of R. sphaeroides that did not make carotenoids—the Q. The result? The stronger the field, the less radical product was made. They have demonstrated a magnetic field effect in an organism for the first time, and the effect was helpful, not damaging. Their next step, which they are working on, is examining whether or not the bacteria grow better in the presence of the fields.

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