Black Queen tells microbes to be lazy

THIS WEEK Field notes CERN, Geneva, Switzerland

Let the antimatter games begin

upcoming experiment called AEGIS to test how antimatter reacts to gravity. “Go after Einstein – the biggest game in town.” Indeed, competition for such glory is fierce, with each of the four teams marking their territory with flags from team members’ universities. “There is definitely more competition than collaboration,” admits Hangst. All four aim to carry out surgically precise measurements “To unlock antimatter’s on antihydrogen, made up of an secrets you have to slow it antiproton and a positron, the to the point where you can anti-electron. Protons produced elsewhere at CERN are smashed into a experiment on an atom” metal target to create the antiprotons, which are then electromagnetically Hangst, who is ALPHA team leader. channelled into the Antiproton “Everyone still rushes over with bated Decelerator – the “mini-LHC” in the breath to see if we have anything.” basement of building 193. From there, That’s bad news for anyone they are sent up through pipes to the dreaming of cadging a ride on an four experiments above, which antimatter-fuelled spacecraft, but combine them with positrons to it’s a start. n

Capturing just one antihydrogen atom is no mean feat 12 | NewScientist | 31 March 2012

Maximilien Brice/CERN

Jessica Griggs

I DESCEND into the bowels of building 193 to particle physics’ version of Bizarro World. Before me lies what looks like a miniature Large Hadron Collider, with superconducting magnets surrounding a 190-metrelong particle track. Instead of accelerating particles, this contraption decelerates them – the only one at CERN built to make particles sluggish. I am at the premier factory for making the most expensive atoms, by weight, on the planet. Here, there is no need for speed because the four experiments in this building are not trying to create collisions powerful enough to give rise to hypothetical entities such as the Higgs boson. Instead, they are trying to unlock the secrets of antimatter, which means slowing antiparticles down enough to carry out experiments – often on a single atom. “With the LHC you have sledge-hammer precision; we need scalpel-precision to carry out experiments on single atoms,” says physicist Jeffrey Hangst. Antiparticles are notoriously slippery test subjects. With the same mass but the opposite charge to ordinary particles, they disappear in a puff of energy whenever they meet normal matter, which makes up everything we see. That means antiparticles have to be painstakingly made and captured for each test. The pay-off stands to be huge. Ordinary matter and antimatter are expected to behave the same way – responding identically to gravity, for instance. If they don’t, it could be the calling card of exotic new forces, beyond those described by the standard model and Einstein’s general relativity. “How do you get famous?” asks Michael Doser, spokesman for an

create antihydrogen atoms. Other than the gravity-testing AEGIS, the other three experiments – ALPHA, ATRAP and ASACUSA – all aim to see if antihydrogen absorbs and emits light at the same wavelengths as hydrogen. ALPHA recently made the first such spectral measurement, but it wasn’t precise enough to detect any differences. Still, any progress is celebrated. Because neutral antihydrogen only responds weakly to electromagnetic fields, the atoms have to be moving very slowly to be captured for study. “We make about 6000 antihydrogen atoms at a time but only catch one or two,” says

Microbes race to throw away vital genes CONFRONTED by a deadly threat, most bacteria let someone else handle it. According to the Black Queen hypothesis, evolution pushes microorganisms to lose essential functions when there is another species around to perform them. The idea could explain why microbes are so dependent on each other. Jeffrey Morris of Michigan State University in East Lansing got the idea from an ocean-dwelling bacterium called Prochlorococcus. “It is the most common photosynthetic organism on Earth,” he says, but for decades no one could grow it. That’s because Prochlorococcus relies on other bacteria to break down toxic hydrogen peroxide. This led Morris to the Black Queen hypothesis, named after the card game Hearts, in which players try to discard the costly queen of spades. For microorganisms every ability is costly – carrying genes and making proteins uses up energy – so they benefit from losing genes if possible. As long as one microbe breaks down hydrogen peroxide all bacteria in the area benefit, so it is in the microbes’ interests to discard the associated genes quickly (mBio, DOI: 10.1128/mBio.00036-12). Morris acknowledges that this kind of outsourcing is a dangerous game to play, though. In theory, all of the microbes may lose the genes at the same time, leaving none to deal with hydrogen peroxide. Unpublished experiments support the Black Queen hypothesis. Morgan created Escherichia coli vulnerable to hydrogen peroxide, then gave them a resistance gene. Many, but not all, of the bacteria promptly lost the gene. William Costerton of the Center for Genomic Sciences in Pittsburgh, Pennsylvania, thinks the idea makes sense. “Some species may be ‘donkey engines’ for whole consortia [that] are unable to grow in the absence of the donkey.” Michael Marshall n