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9 March 2013 | NewScientist | 17 Wanted: immune system thief TALK about turning the tables. A bacterium evolves an immune system to protect itself from a virus. Then, the virus steals the immune system and uses it to attack the bacterium. The ICP1 virus was discovered in Bangladesh where it infects the cholera-causing Vibrio cholerae bacterium. Like other bacteria, V. cholerae stores DNA from viruses that infect it, so it can recognise and destroy them next time they meet. Andrew Camilli of Tufts University in Boston and his team found that ICP1 also has copies of bits of the cholera bacterium’s crucial defensive DNA. The virus seems to turn the weapon back on its host by attacking the immune system of the bacterium, leaving the organism open to infection. When Camilli and his colleagues mutated the stolen sections of ICP1’s genome, the virus lost its ability to infect the bacterium (Nature, doi.org/kn7). It is yet another twist in the endless battle between bacteria and viruses, says John van der Oost of Wageningen University in the Netherlands. “You have every kind of warfare you can think of in the microbial world.” Dark matter alternative gets a galactic gravity boost DWARF galaxies circling the spiral galaxy Andromeda have boosted a little-fancied rival to the idea of dark matter – the invisible stuff thought to make up about 80 per cent of the universe’s matter. Modified Newtonian dynamics, or MOND, uses tweaked versions of Newton’s laws of motion and gravity to explain effects attributed to dark matter. For one, stars on the edges of galaxies are zooming around too fast for the gravitational pull of the mass we can see, and should be flung off. The usual explanation is that the gravity of dark matter prevents this, but MOND says an object in a weak gravitational field – like that at the edge of a galaxy – will feel a slightly stronger pull than Newton would have predicted. Mordehai Milgrom at the Weizmann Institute in Rehovot, Israel, and Stacy McGaugh of Case Western Reserve University in Cleveland, Ohio, used MOND to model the motion of such objects. Then they compared their results with new data on stellar motion in 17 Andromeda satellite galaxies (arxiv.org/abs/1301.0822). LAST September, unbeknown to most earthlings, a ring of radiation formed around our planet and lingered for four weeks. We know that two belts of charged particles, the Van Allen radiation belts, constantly encircle Earth, trapped by its magnetic field. The inner belt extends from 1600 to 12,900 kilometres above ground and is fairly stable. But the outer belt, stretching from 19,000 to 40,000 km above ground, can grow in size by a factor of 100 over minutes or hours. This happens when its electrons are accelerated to nearly the speed of light, for reasons that remain unclear. During one such acceleration event on 2 September, an extra ring formed in between the two belts. It was spotted by NASA’s twin Van Allen probes, then only a few days into their mission. They also saw it being destroyed on 1 October by a shock wave, probably linked to a burst of solar activity, report Dan Baker of the University of Colorado, Boulder, and colleagues (Science, doi.org/kpb). It’s not clear whether the new ring formed from the inner or outer ring, but figuring out what happened could help protect spacecraft from radiation. Mystery radiation ring encircles Earth JHU/APL, FROM REPT DATA/LASP “Our predictions are spot on,” McGaugh says. However, MOND is not widely accepted because it is not clear why gravity’s pull should change in weaker fields. And although MOND works well for stars moving in galaxies, it fails to predict the speeds at which galaxies in clusters orbit each other. James Binney at the University of Oxford says some sort of MOND-like behaviour may apply within galaxies while on larger scales, as in galactic clusters, dark matter would hold sway. Rainy day in LA? Blame the Sahara IF THE Sahara gets any drier, it could make California wetter. That’s because the dust and microbes that help form clouds can travel around the world on narrow air streams, causing rain. The particles help clouds form by acting as seeds for water vapour to condense around. “Atmospheric rivers” carry this dust-laden water until they hit mountains, such as California’s Sierra Nevada, where their cargo turns to precipitation. To see how these rivers affect weather, Kimberly Prather and colleagues at the University of California, San Diego, flew planes through six storms over the Sierra Nevada in 2011, gathering particles from the air. They also collected samples of rain and snow. The team was able to identify the type and origin of the particles by analysing their chemistry and using satellite data to model where the storms’ air currents began. The storms picked up the vast majority of particles over Asia. In some cases, dust had been picked up earlier, over the Sahara and the Middle East (Science, doi.org/kpm). In two storms with otherwise identical conditions, the one containing more dust was much wetter. In future, extra dust from desertification and activities such as agriculture could make far-flung places wetter, says Prather. ROBERT GALBRAITH/REUTERS For new stories every day, visit newscientist.com/news
