This image shows a colony ofTrichodesmium.

 DNA of bacteria crucial to ecosystem defies explanation

Scientists have found something they can't quite explain in one of the most barren environments on Earth: a bacterium whose DNA sequence contains elements usually only found in a much higher organism.

This is becauseTrichodesmium is a "nitrogen fixer" -- it makes harsh environments more habitable by turning nitrogen gas from the air into ammonium, a nutrient that other organisms can use. It's foundational to the entire food web of the ocean and therefore an important organism for scientists to understand.Trichodesmium is a type of bacteria known as an oligotroph, meaning that it can survive in incredibly nutrient-poor regions of the ocean. In fact, it thrives there -- to the point that great blooms of the microorganism can be seen both with the naked eye and from satellites in space, earning it the name "sea sawdust" from ancient mariners.

By sequencing multiple Trichodesmium genomes -- and using a wide variety of samples to ensure that there was no error -- researchers found that only about 63 percent of the bacteria's genome is expressed as protein. That's an incredibly low amount for a bacterium and unheard of for a free-living oligotroph.

"Our study adds another wrinkle to this enigmatic organism's story," said Eric Webb, associate professor at the USC Dornsife College of Letters, Arts and Sciences and corresponding author of a study on the finding.

In a paper published in March in the Proceedings of the National Academy of Sciences, Webb and his colleagues revealed that Trichodesmium's DNA defies common evolutionary dogma, meaning that there's either an important piece of the puzzle still missing or that the understanding of the evolution of microbial genomes needs to be revisited.

"The unique evolutionary path reflected in this genome contradicts nearly all accounts of free-living microbial genome architectures to date," said lead author Nathan Walworth, a Ph.D. candidate at USC. "Different evolutionary paths are foundational to all arenas of biology, including biotechnology, so it is important for the field to be cognizant of different paths a living organism can take to achieve ecological success."

When scientists first started sequencing genomes in the last century, they found that not every part of the DNA strand encoded a protein to be expressed. In fact, we now know that only about 2 percent of the human genome is expressed -- the rest was initially called "junk DNA."   

Scientists now describe it as "non-coding DNA," a nod to the fact that functions have been defined for many of these regions; however, there is still controversy on the extent and role of these regions.

Despite the uncertainty, higher organisms -- like humans -- with tiny populations are highly vulnerable to sweeping mutations and thus can contain a lot of non-coding DNA.

Lower organisms with huge populations -- like bacteria -- are far less susceptible to sweeping mutations and accordingly have been shown to have genomes that are about 85 percent protein coding.

Oligotrophs, in particular, shun non-coding DNA, possibly because of the high energy-cost of living in a harsh environment. Cells need every ounce of energy simply to replicate and survive.

Trichodesmium, as Webb and his team discovered, breaks the mold. Yet despite the novelty of the finding, the ultimate cause of the large non-coding space remains to be defined.

The team theorizes that the high level of non-coding DNA is likely the result of a combination of factors, possibly including the way that Trichodesmium blooms.

Blooms make the species more vulnerable to genetic drift and can lead to genomes with enriched non-coding DNA.

"However, since there are many other bloom-forming cyanobacteria that that do not have expanded non-coding space, blooming ecology is likely not the whole story," Webb said. "Right now, we speculate that interactions with other undefined organisms might also be important."

The surprising and odd nature of Trichodesmium's DNA represents a new and open issue in the study of genetics and one, given the organism's overall importance, that the researchers are eager to answer.

Electrons move like light in three-dimensional solid

Artist’s conception highlighting key features of electron behavior in bulk sodium bismuth and cadmium arsenic. The interactions in the three-dimensional lattice lead to electrons that travel at a fixed velocity, independent of the electron’s energy state

Electrons were observed to travel in a solid at an unusually high velocity, which remained the same independent of the electron energy. This anomalous light-like behavior is found in special two-dimensional materials, such as graphene, but is now realized in a three-dimensional bulk material. High-resolution angle-resolved electron spectroscopy, stimulated by synchrotron x-ray radiation, was used to substantiate the theoretically predicted exotic electron structure.

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A stable bulk material has been discovered that shows the same physics found in graphene, which illuminated the detailed interactions of electron's orbital motion and its intrinsic magnetic orientation. The new material will be a test ground for theories on how electron interactions in solids shape exotic electron behavior, including the highest electron mobility in bulk materials.

Investigations of electronic behavior have expanded beyond familiar systems of metals, insulators, and semi-conductors into the realm of strongly interacting electrons, which exhibit exotic relationships between the allowed electron velocities and their energy states. A key feature for the new materials is behavior in which the electron velocity does not depend on its energy. Such a relationship is a hallmark of photons, the energetic particles that make up a beam of light. This property is found in the new class of materials exhibiting a strong interaction between the electron trajectory and the electron spin alignment (called "spin-orbit coupling"). Two-dimensional versions of such systems (for example, grapheme) have been recently explored, but the systems are hard to work with because of their ultra-thin film nature.

This work establishes graphene-like electronic behavior in the bulk three-dimensional materials Na₃Bi and Cd₃As₂ and explains their exceptionally high electronic mobility. The required advances in electron spectroscopy techniques, used to investigate the electronic structure, employed an energy tunable bright x-ray source and a high-resolution spectrometer.

    

Exploding stars help to

understand thunderclouds on

Earth

This shows a particle shower initiated by a cosmic ray reaches LOFAR through a thundercloud.

Credit: Radboud University

[Click to enlarge image]

How is lightning initiated in thunderclouds? This is difficult to answer -- how do you measure electric fields inside large, dangerously charged clouds? It was discovered, more or less by coincidence, that cosmic rays provide suitable probes to measure electric fields within thunderclouds. This surprising finding is published in Physical Review Letters on April 24th. The measurements were performed with the LOFAR radio telescope located in the Netherlands.

'We used to throw away LOFAR measurements taken during thunderstorms. They were too messy.' says astronomer Pim Schellart. 'Well, we didn't actually throw them away of course, we just didn't analyze them.' Schellart, who completed his PhD in March this year at Radboud University in Nijmegen and is supervised by Prof. Heino Falcke, is interested in cosmic rays. These high-energy particles, originating from exploding stars and other astrophysical sources, continuously bombard Earth from space.

High in the atmosphere these particles strike atmospheric molecules and create 'showers' of elementary particles. These showers can also be measured from the radio emission that is generated when their constituent particles are deflected by the magnetic field of Earth. The radio emission also gives information about the original particles. These measurements are routinely conducted with LOFAR at ASTRON in Dwingeloo, but not during thunderstorms.

Modeling

That changed when the data were examined in a collaborative effort with astrophysicist Gia Trinh, Prof. Olaf Scholten from Groningen University and lightning expert Ute Ebert from the Centrum Wiskunde & Informatica in Amsterdam.

'We modeled how the electric field in thunderstorms can explain the different measurements. This worked very well. How the radio emission changes gives us a lot of information about the electric fields in thunderstorms. We could even determine the strength of the electric field at a certain height in the cloud.' says Schellart.

This field can be as strong as 50 kV/m. This translates into a voltage of hundreds of millions of volts over a distance of multiple kilometers: a thundercloud contains enormous amounts of energy.

Dangerous charge

Lightning is a highly unpredictable natural phenomenon that inflicts damage to infrastructure and claims victims around the world. This new method to measure electric fields in thunderclouds will contribute to a better understanding and ultimately better predictions of lightning activity. Current measurement methods from planes, balloons or little rockets are dangerous and too localized. Most importantly the presence of the measurement equipment influences the measurements. Cosmic rays probe the thunderclouds from top to bottom. Moving at almost the speed of light they provide a near instantaneous 'picture' of the electric fields in the cloud. Moreover, they are created by nature and are freely available.

'This research is an exemplary form of interdisciplinary collaboration between astronomers, particle physicists and geophysicists', says Heino Falcke. 'We hope to develop the model further to ultimately answer the question: how is lightning initiated within thundercloud
s

island surrounded by methane and ethane

Titan’s Magic Island

Saturn’s largest moon, Titan, might be the most intriguing member of the solar system. It’s a primeval Earth, complete with an atmosphere, liquid bodies, and even suggestions of geological activity.

In 2013, the orbiting Cassini spacecraft spotted a brand new chunk of land that mysteriously appeared out of Titan’s second-largest sea, Ligeria Mare. Shortly thereafter, the “Magic Island” disappeared just as mysteriously into the translucent, –200 degree Celsius (–290 °F) methane-ethane sea. And then itreappeared again as a much larger landmass during one of Cassini’s recent radar sweeps of Titan.

The transient land confirms the supposition that Titan’s alien oceans and seas are dynamic components of an active environment, rather than static features. However, astronomers are at a loss to explain the physical processes responsible for the ephemeral landmass. Especially since it appears to have doubled in size—from 50 to 100 kilometers (30 to 60 mi) across—since it reappeared.

moons magnetic secret

The Moon’s Mysterious Magnetic Field

Photo credit: Mark A. Wieczorek

The Moon has remained magnetically inert for eons, but new research confirms that this was not always the case. Over four billion years ago, an inner molten moon-core whirled against a lunar mantle, much like Earth’s own dynamo, and a potent magnetic shield extended from the Moon. But this was presumably a much weaker version than Earth’s, since the satellite obviously lack’s Earth’s heft, right?

Surprisingly, our scrawny little moon was actually able to generate a mightier field than ours. No one knows why such a puny body displayed such potent magnetic activity, with current answers running the gamut from “we don’t know” to “magic?” The mystery reveals that there’s yet another unknown set of variables regarding our most intimately studied partner. It appears the early Moon took advantage of some exotic method to produce its awesome magnetic field. And it managed this for longer than astronomers previously thought was possible, perhaps due to constant meteor impacts that fueled Luna’s magnetism.

It appears that the field disappeared sometime around 3.8–4 billion years ago, though more research is necessary to find out exactly why. Surprisingly, studies suggest that the Moon’s core is still at leastslightly liquid. So even though the Moon is within reaching distance, we’re constantly reminded that there are many fundamental questions we’ve yet to answer about lunar geology.