ELECTROPHYSIOLOGY

On the pulseAppl. Phys. Lett. 93, 033906 (2008)They’re a staple of every hospital television show: to get the beeping signal of an electrocardiograph, medics hurriedly attach electrodes to a patient’s skin. Now Robert Prance and his colleagues at the University of Sussex in Brighton, UK, have found a way to measure the electrical signals of a person’s breathing and heartbeat remotely.

Their sensor detected clear signals from both the front and back of a seated subject, up to 40 centimetres away, in a laboratory full of distracting electrical noise. Other techniques exist that can remotely discern the tiny movements of the heart and lungs, but those systems actively irradiate their subject with laser light or microwaves.

The researchers note that their passive system could be used for security and healthcare, and perhaps even to detect driver drowsiness.

MICROBIOLOGY

Running on arsenicScience 321, 967–970 (2008)Arsenic-fuelled photosynthetic bacteria may have helped shape the arsenic cycle on ancient Earth.

The newly discovered bacteria use electrons from arsenite to drive photosynthesis in the absence of oxygen, producing arsenate in the process. Ronald Oremland of the US Geological Survey in Menlo Park, California, and his co-workers found the microbes growing in red and green mats in arsenite-rich brine pools (pictured right) at Mono

Lake, California. A pure culture of one purple bacterium isolated from the red mats required both light and arsenite to thrive.

Although other bacteria are known to rely on arsenic, this is the first example of the photosynthetic use of arsenite in the absence of oxygen. The process could have been important on Earth before oxygenic photosynthesis reshaped the atmosphere.

FLUID DYNAMICS

Slip and slidePhys. Rev. Lett. 101, 064501 (2008)A principle of fluid flow is that the bottom-most molecules of a liquid stick to the surface of the solid they are sliding past — creating friction that, for instance, slows down water flowing through a pipe.

Choongyeop Lee at the University of California, Los Angeles, and his colleagues created textured surfaces with micrometre-scale grooves and posts. On these, fluids can slip past friction-free for tiny distances, coasting on the pockets of air between the

grooves or posts. They report a slip length for water almost ten times longer than previously achieved — long enough, they suggest, to show that engineered surfaces can significantly reduce drag in fluid systems.

ATMOSPHERIC CHEMISTRY

Attacked from withinJ. Am. Chem. Soc. doi 10.1021/ja8041965 (2008)Organic compounds in the lower atmosphere can be attacked by the particles they are sitting on, according to researchers at the University of California, Irvine.

Lab-based experiments by Barbara Finlayson-Pitts and her colleagues show that airborne sea-salt particles containing nitrate or nitrite ions can produce reactive hydroxyl radicals that attack the organic compounds adsorbed onto the particles’ surfaces. It was previously thought that oxidation of these organics occurred through attack from outside by ozone or hydroxyl radicals.

Nitrate and nitrite ions are known to be present in many atmospheric particles and in the polar snowpacks. On the basis of the group’s experiments, Finlayson-Pitts says it is highly likely that this bottom-up oxidation is happening in air, and could be contributing to atmospheric chemistry.

CLIMATE INDICATORS

Early birdsGlobal Change Biol. 14, 1959–1972 (2008)The first robin sighting of spring may not be the best indicator of climate warming.

Abraham Miller-Rushing at Boston University and his colleagues analysed 33 years’ worth of data on 32 bird species in

Don’t you step on my…Behav. Ecol. Sociobiol. doi:10.1007/s00265-008-0620-6 (2008)

Among blue-footed boobies, bright blue feet are known to be important for courtship, but it seems that’s not all they’re good for. Researchers now find that if male feet lose colour after a first egg is laid, females reduce their reproductive efforts.

Roxana Torres at the National Autonomous University of Mexico in Mexico City and her colleagues monitored pairs of the birds (Sula nebouxii) on Isla Isabel, off the coast of Mexico. In general, boobies lay two eggs of similar weight each year, with an average delay of four days between the two. The team captured males within 24 hours of the first egg being laid and used crayons to make the foot colour of half the males duller and so less healthy looking.

The researchers found that females paired with males that returned with unsavoury feet delayed laying their second eggs and, when they did lay them, produced smaller eggs than did females with untampered mates.

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Massachusetts. They found that the first sighting of a migratory bird, although one of the most commonly used statistics, can be confounded by population size. As bird numbers decline, there are fewer early outliers, making the first birds harder to spot. By extension, growing populations are expected to distort results in the opposite direction.

Instead, the team used the mean arrival date, which did not change with population size. Overall, the birds’ mean arrival was two and a half days earlier by the end of the period covered by the data set than at the start.

ANIMAL BEHAVIOUR

Crowd controlAm. J. Primatol. doi:10.1002/ajp.20601 (2008)Many researchers would expect parasitic infection rates to increase as groups of animals get bigger and more hosts are available. Contrary to this, researchers reveal that as groups of red colobus monkeys (Procolobus rufomitratus) get larger, they have fewer parasites.

Tamaini Snaith at McGill University in Montreal, Canada, and her colleagues made the discovery while studying the monkeys in Uganda. They tested faeces for parasites and monitored group dynamics. The researchers noticed that large groups tended to spread out more than smaller ones, and suggest that this could lower infection rates.

They add that although the monkeys may be spreading out in response to the parasites, feeding competition could also be driving the spread, making the parasite reduction a happy accident.

IMMUNOLOGY

The power of tick spitJ. Exp. Med. doi:10.1084/jem.20072689 (2008)Proteins used by ticks to evade their hosts’ immune systems may one day provide a new way to fight inflammation, researchers say.

Compounds in tick saliva block inflammation and allow the bloodsucking parasites to feed off a host for long time periods without alerting its immune system. Amanda Proudfoot and Christine Power of Merck Serono Geneva Research Centre in Switzerland and their team isolated a family of tick saliva proteins that very selectively bind specific pro-inflammatory members of a protein family called chemokines.

Two of these proteins, which have been named evasins, produced no obvious allergic reaction and reduced inflammation when given to mice suffering from several conditions, including skin or joint inflammation and lung injury.

BOTANY

Biofuel heir apparent?Global Change Biol. 14, 2000–2014 (2008)The perennial grass Miscanthus × giganteus (pictured below) is photosynthetic royalty. In field tests conducted by Stephen Long and his co-workers at the University of Illinois in Urbana, this sterile hybrid converted 1% of solar energy into biomass that could be harvested to make cellulosic ethanol. That’s ten times the standard 0.1% efficiency cited for plants in general.

The team compared Miscanthus with switchgrass (Panicum virgatum), a current US favourite for the cellulosic fuel of the future. Miscanthus produced an average of 30 tonnes of harvestable biomass per hectare; switchgrass produced just 10 tonnes.

BIOPHYSICS

Mob ruleProc. Natl Acad. Sci. USA 105, 11754–11759 (2008)The crowding inherent within cells may affect not only protein movement and folding, but also shape, according to Pernilla Wittung-Stafshede at Rice University in Houston, Texas, and her colleagues.

They focused on the VlsE protein, a proposed virulence factor in Borrelia burgdorferi, the bacterium that causes Lyme disease. VlsE is usually rugby-ball shaped, but the team found that it adopts different equilibrium shapes in vitro in the presence of varying levels of a polymeric ‘crowding agent’ that mimics cytoplasmic macromolecules. When the native protein is loosened up by a denaturing agent or by heat, two new structures — a ‘bean’ shape and a roughly spherical conformation — intervene between the rugby ball and the denatured protein as soon as the crowding agent is added.

If crowding can be ‘tuned’, it might be possible to expose different sites in proteins and alter their behaviour.

Discuss this paper at http://blogs.nature.com/nature/journalclub

Michelle D. WangHoward Hughes Medical Institute, Cornell University, Ithaca, New York

A biophysicist marvels at the idea of grabbing microscopic particles with light by tweaking its phase.

Light carries energy and momentum. Have you ever gazed at a comet on a hot summer night? The dust tail seen streaming out from a comet is caused by sunlight bombarding dust particles from its surface and pushing them away from the Sun. The same radiation pressure can be used to ‘trap’, or hold, microscopic particles. And if an item of interest — for example, a biological molecule — is attached to a particle subject to trapping, it can then be manipulated as the trap is moved.

So how does one generate optical traps? Conventionally, a laser beam is directed through the objective lens of a microscope and focused to a small spot very close to the specimen. The trapping force relies on the gradient of the laser’s intensity — the tighter the focus, the greater the intensity change within the focused beam, and the greater the trapping force.

For a long time, this has been the only type of trap available. But not any more! David Grier and his colleagues have created a new type of trap that relies on the gradient of the ‘phase’ of a laser’s light as well as its intensity (Y. Roichman et al. Phys. Rev. Lett. 100, 013602; 2008). Light waves, like ocean waves, have crests and troughs. The phase of a light wave specifies what position within the wave, from crest to trough, the light is in at a given moment. By tweaking the phase of the laser in the trap, the researchers are able not only to hold a particle steady, but also to move it in a line or spin it around in a circle. It is now possible to design optical traps that are more flexible and versatile, and that can generate as much trapping force as before, but with less light.

I would not be surprised if these traps soon become one of the must-have tools in single-molecule biophysics, cell biology and colloidal physics.

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NATURE|Vol 454|21 August 2008