16 | NewScientist | 24 August 2013

HYPERSWARMING bugs are not as scary as they sound. In fact, the way disease-causing bacteria in the lab evolve to spread more rapidly than wild versions could be used against them. Joao Xavier from the Memorial Sloan-Kettering Cancer Center in New York and colleagues placed colonies of Pseudomonas aeruginosa at the centre of nutrient plates and let them

spread to form a biofilm. The films are a hallmark of infection when the bacteria infects humans. After 24 hours, the team scraped up all of the bacteria and placed small samples in the centre of new plates to spread again.

After nine days of repeating this procedure, some colonies began spreading more rapidly across the plates – a behaviour the team dubs “hyperswarming”. Despite

Galaxy shapes set near cosmic dawn

OUR galactic zoo evolved into recognisable species a mere 2.5 billion years after the big bang.

Today, disc or spiral galaxies are mostly blue, a sign that they are forming new stars, while blobby spheroidal galaxies are red and are no longer making many stars.

To see how far back this pattern existed, Mauro Giavalisco of the University of Massachusetts in Amherst and colleagues looked at pictures of massive galaxies taken by the Hubble Space Telescope. The team focused on an early era when star formation was at its peak. They found the same familiar breakdown of shapes and colours in more than 1000 massive galaxies (The Astrophysical Journal, doi.org/nhv).

The results will help cosmologists sort out which of the processes that go into galaxy building are the most important for defining cosmic structure over time.

Do you know the speed limit? That barn owl does

BIRDS cannot read road signs, but they know that some roads have higher speed limits than others. They will take off further away from an approaching car on a faster road than on a slower road – regardless of the speed of the car.

When Pierre Legagneux of the University of Quebec at Rimouski and Simon Ducatez of McGill University in Montreal, both in Canada, were working together in France in 2006, they began studying the birds they encountered on the drive home from the lab. They found that where there was a 50-kilometre-per-hour speed limit, birds on the road typically took off when the car

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Aggressive bacteria have a weakness spreading faster, hyperswarms were less able to stick together to form dangerous biofilms.

The change was down to a single mutation in their DNA that allowed the bacteria to develop several whip-like flagella for movement instead of just one (Cell Reports, doi.org/nhm).

The results suggest that therapies encouraging the bacteria to mutate into a hyperswarming form could make them less harmful.

was about 15 metres away, whereas on a 110-km-per-hour road, they took off when a car was nearer 75 metres away. They did this even when faced with a car travelling faster on the slow road or slower on the fast road.

The researchers think the birds treat cars as predators, and realise that in some parts of their environment the predators are more dangerous than in others (Biology Letters, DOI: 10.1098/rsbl.2013.0417).

“Birds are able to associate environments, like forests or roads, with risk,” says Christopher Lepczyk, an ornithologist at the University of Hawaii, Manoa. He thinks the work could prompt follow-up studies comparing birds in urban and rural areas, and perhaps encourage more innovative methods. “I just think it’s really cool,” he says. “We don’t do enough of this kind of work.”

YOUTHFUL runaways are nothing new – even in space, where a brush with a black hole can eject young stars from the galaxy. Now the first old stars have been spotted on course to leave the Milky Way.

The pair of white dwarfs, named LP 400-22, probably had another companion, says Mukremin Kilic of the University of Oklahoma in Norman. But the trio swung too close to a black hole at the centre of their star cluster. It gobbled up the third star, which transferred a huge amount of energy to the white dwarfs, ejecting them at such speed that they will eventually leave the galaxy behind (arxiv.org/abs/1307.3258).

Observing such runaway stars can help reveal the tug of invisible dark matter in the Milky Way.

Elderly star couple flees the galaxy

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