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June 10, 2011 9:54 pm

Could arsenic be life-giving?

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A moonlit night at Mono Lake, California

Microbes found in Mono Lake, California, above, have excited considerable scientific debate

Last year’s most controversial research paper, describing a “weird” microbe that uses arsenic instead of phosphorus in its DNA and other biological molecules, has come under sustained scientific attack. But the authors are sticking to their guns.

The study, funded partly by Nasa’s astrobiology programme, caused a sensation when it appeared in the journal Science in December, because the bacteria were the first to use an element beyond biology’s big six – CHNOPS, or carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur – for its biochemistry.

Although the GFAJ-1 bacteria were terrestrial in origin, extracted from the arsenic-rich mud of Mono Lake in California, they seemed to open up new chemical possibilities for the existence of life in very different environments beyond Earth.

The conclusion – that the bacteria use arsenic when phosphorus is excluded from their culture dishes – provoked a critical onslaught. Science selected eight papers attacking the research, which it published last week as “technical comments”, each accompanied by a response from the original authors.

Some of the critics believe the experiments failed to exclude small quantities of phosphorus that could have been sustaining the microbes rather than arsenic, or that contamination accounted for the detection of arsenic in the bacterial DNA. Others argued on biochemical grounds that arsenic could not replace phosphorus in a living cell.

For example, Steven Benner, of the Foundation for Applied Molecular Evolution in Florida, a leading expert on exotic biochemistry, points out that the form of arsenic that would be expected in DNA – compounds called arsenate esters – would probably be very unstable in the bacteria. And he argues that the microbes may have scavenged traces of phosphorus from an impurity unknown to the experimenters.

The research team, led by Felisa Wolfe-Simon at the Nasa Astrobiology Institute in California, concede some minor points but maintain that their overall conclusion stands: the GFAJ-1 bacteria were substituting arsenic for some phosphorus in biomolecules.

The journal points out that these eight critiques and responses are far from being the final word. There will be renewed attempts to replicate the findings – and, to help the process, Wolfe-Simon and colleagues are offering samples of GFAJ-1 to other scientists. Meanwhile, they are gathering more evidence, which they plan to publish in due course.

“That we received so much feedback ... suggests to us that science is proceeding as it should,” Science’s editors say. “We hope the study and the subsequent exchange will stimulate further experiments, whether they support or overturn this conclusion. In either case, the overall result will advance our knowledge about conditions that support life.”


Ayurveda goes under the microscope

Ayurveda, the Indian medical system, has evolved over 2,000 years or so into a structure of considerable complexity. It was passed down first through oral tradition, then written in Sanskrit, copied and recopied, altered accidentally and deliberately – so that today people are not sure which of the original messages survive.

Researchers in Austria are embarking on a project to reconstruct as authentic a version of the ancient Ayurveda as they can, using a scientific approach that includes evolutionary biology. They are focusing on the eight-volume Caraka Samhita, the most ancient and important of Ayurvedic treatises, and in particular its third and fourth volumes, the “Vimanasthana” and “Sarirasthana”.

“These sections actually deal with fundamental topics in Ayurvedic thinking,” says Karin Preisendanz of the University of Vienna, the project leader. “Knowledge about human anatomy, embryology, pathology and the natural healthy state was written down in them, as well as thoughts about and ways of realising a full lifespan.”

To discover which of the surviving “mutated texts” reflect most accurately the original way of thinking, the researchers are applying computer-based methods used previously to work out evolutionary relationships between species through genetic analysis.

The aim is to get as close as possible to the ancient original texts. Besides reconstructing an “archetypal version”, Preisendanz and her team will build a “critical edition” that is annotated with the analytical methods used and presents the story of the work’s transmission over the centuries.

The Austrian Science Fund, which is supporting the project, says it builds on Vienna’s long tradition of Sanskrit scholarship.


A bird’s-eye view of Himalayan migration

Satellite tracking tags have revealed the migratory secrets of the world’s highest flying birds, Asia’s bar-headed geese.

In spring, the geese fly northward from their wintering grounds at sea level in eastern and southern India, and up over the Himalayas at an altitude of 6,000m, to reach their summer breeding territory in Mongolia in a single day without resting. They make the reverse journey in the autumn.

Ornithologists had assumed that the strikingly patterned geese wait for upslope tailwinds, which typically develop on spring afternoons, to lift them over the mountains. But in fact they make the climb in the relatively still, cold air of the night and early morning.

“We think the geese may be essentially risk-averse, with the calmer winds at night offering an extra degree of safety and helping to avoid storms,” says Charles Bishop of Bangor University, head of the international research team whose work is reported in Proceedings of the National Academy of Sciences.

“We were amazed to see that the geese were maintaining these climbs for hours on end,” adds his colleague Lucy Hawkes. “It seemed quite enough that they could cope with such intense exercise at altitude, let alone that they didn’t stop to take regular breaks during the climbs, which last for at least seven hours over the Himalayas.”

At 6,000m the air has less than half the oxygen that it does at sea level. The peak of Mount Everest is 8,840m above sea level.


Letting the cat out of the bag on litter

Cat litter is a surprisingly large and (in environmental terms) dirty market. The granules, whose UK sales exceed £60m a year, are made mainly from sedimentary clay transported from countries with relatively lax rules for quarrying and mineral processing.

Next year, however, will see the launch of a “clean tech” cat litter made from “quarry fines” – the dust and fine particles that accumulate as waste at many working quarries in Britain. The project is funded and organised by the Technology Strategy Board, with Imperial College London providing the scientific input and Bob Martin, the pet product company, the commercial outlet.

Christopher Cheeseman’s team at Imperial has found a way to bind fines into granules using an organic binding agent and to coat them with super-absorbent polymer. “We have made the quarry waste into an effective carrier for a small amount of active ingredient, the super-absorbent polymer,” he says.

The new material has the required water absorption capacity (above 80 per cent), while not producing dust in the litter tray.

Bob Martin expects to set up a small number of production units as close as possible to the sources of quarry waste, each one capable of producing 15,000 tonnes a year of cat litter. The total UK market requires 280,000 tonnes a year – and the US takes 5m tonnes a year.

The company expects to double its European sales within a year of the product becoming available. And cat litter may just be the start for this technology. The researchers are already eyeing up other possible uses, including soil remediation products and de-icing grit.

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