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Land powered by the rising sun
New Scientist 10 Feb 2001

JAPAN plans to build an orbiting power station to harvest solar energy and beam it back to Earth. The newly formed Ministry of Economy, Trade and Industry (METI) wants to start research into the Space Solar Power System this year and begin operations in 2040.

The proposed satellite would weigh around 20,000 tonnes, be lifted to geostationary orbit in several stages and have two solar panels each measuring three kilometres by one kilometre. The station would convert solar energy into microwaves and beam them back to Earth from a one-kilometre antenna. Osamu Takenouchi of METI says the microwaves would not interfere with cellphones or other communications on Earth.

METI estimates that it will have to spend around fil.5 billion on construction at today's prices. NASA shelved a similar project because of the huge costs involved. Once in place, the station would produce 1 gigawatt of power at a cost of 13.5 pence per kilowatt hour, compared to around 5 pence for conventional power sources in Japan today.

Tests on the energy-delivery system have already been completed by an airship that beams microwaves to Earth. Researchers are now trying to make cheaper and more efficient solar cells. 'This kind of energy source will also become more important as global warming increases," says Takenouchl.

Molly Macauley at Resources fbr the Future in Washington DC, author of the NASA report, "Can power from space compete?" says the possible long-term health effects of such high power densities at ground stations could be a problem. "Even if there tumed out to be little or no scientific data to support possible harm, public 'perception' may hinder deployment," she wams. Peter Hadfield

Burn it down New Scientist 10 Feb 2001
Setting fire to small patches of rainfbrest may do more good than harm

LOW-LEVEL slash-and-burn farming doesn't harm rainforest. On the contrary, it helps farmers and improves forest soils. This is the heretical view of a German soil scientist who has shown that burnt clearings in the Amazon, dating back more than a thousand years, helped create patches of rich, fertile soil that farmers still benefit from today.

Most rainforest soils are thin and poor because they lack minerals and because the heat and heavy rainfall destroy most organic matter in the soils within four years of it reaching the forest floor. This means topsoil contains few of the ingredients needed for long-term successful farming.

But Bruno Glaser of the Institute of Soil Science and Soil Geography at the University of Bayreuth has studied unexpected patches of fertile soils in the central Amazon. These soils contain lots of organic matter. Glaser has shown for the first time that most of this fertile organic matter comes from "black carbon"-the detritus from smouldering camp fires and charred wood and charcoal left over from thousands of years of slash-and-burn farming. "The soils, known as Terra Preta, contained up to 70 times more black carbon than the surrounding soils," says Glaser.

Unburnt vegetation rots quickly, but black carbon persists in the soil for many centuries. Radiocarbon dating shows that the charred wood in Terra Preta soils is typically more than a thousand years old.

"Slash-and-burn farming can be good for soils provided it doesn't completely burn all the vegetation, and leaves behind charred wood," says Glaser. "It can be better than manure." Burning the forest just once can leave behind enough black carbon to keep the soils fertile for thousands of years. And rainforests easily regrow after small-scale clearing. Contrary to the conventional view that human activities damage the environment, Glaser says: "Black carbon [combined with] human excrement and residues from hunting and fishing are responsible for the richness of Terra Preta soils."

Terra Preta soils turn up in patches of a few hectares all over the Amazon, where they are highly prized by farmers. All the patches fall within 500 square kilometres in the central Amazon, between the rivers Tapajos and Curua-Una. Glaser says the widespread presence of pottery confirms the soil's human origins.

The findings add weight to the theory that large areas of the Amazon have recovered so well ftom past periods of agricultural use that the regrowth has been mistaken by generations of biologists for 'virgin" forest.

During the past decade, researchers such as Anna Roosevelt of the Chicago Field Museum of Natural History have discovered hundreds of large earth works deep in the jungle. They are up to 20 metres high and cover up to a square kilometre. She claims that these mounds, built between AD 400 and 1400, were at the heart of urban civilisations. Now it seems the fecundity of the Terra Preta soils may explain how such civilisations managed to feed themselves. Fred Pearce

Green monster Devices for cleaning car exhausts are backfiring on the environment
New Scientist 10 Feb 2001

CATALYTIC converters, which were designed to clean up car exhausts, are polluting the environment. Italian and French researchers have found heavy metals from the devices in remote regions of Greenland. "The fact that we found the metals in Greenland means that it's a global problem. It's not just close to the cities or the highways," says chemist Carlo Barbante of the University of Venice.

Seth Dunn of the Worldwatch Institute, an environmental watchdog based in Washington DC, agrees. "They have broken new ground," he says. "The implications could be very significant in terms of human health." For instance, workers involved in refining platinum, one of the metals used in catalytic converters, are known to suffer from higher than normal levels of severe asthma.

The US, Canada and Japan introduced cars with catalytic converters in the mid1970s. Europe followed in the early 1990s. In these devices platinum, palladium and rhodium catalyse reactions that convert hydrocarbons, carbon monoxide, and nitrogen oxides into less noxious emissions. A recent European Commission study found that exhausts from fast-moving cars erode catalytic converters, ejecting microscopic particles containing the metals.

To assess the global impact of these particles, Barbante and his colleagues went to central Greenland and extracted ice and snow cores dating from 1969 to 1988 and from 1991 to 199S. They also took samples from the Greenland Ice Core Project, dating back nearly 7SOO years.

They found that metal concentrations in the snow have been rising steadily since 1976. Rhodium levels are already 120 times higher than in the 7500-year-old ice. Palladium and platinum levels have increased 80 and 40-fold respectively. The ratio of platinum to rhodium in the snow from the mid-1990s resembled the ratio in car exhausts from another study. This suggests that most of the increased platinum and rhodium comes from catalytic converters, Barbante says.

According to the European Commission study, concentrations of these metals in urban air are still too low to create a significant health risk. But the metals, especially palladium, can accumulate in plants and animals, and enter the food chain. Researchers have found that the freshwater crustacean, Asellus aquaticus, absorbs palladium from sediment. 'We know palladium gets off the catalytic particle and is transferred into the biological system, but we don't know how, " says environmental chemist Greg Morrison of Chalmers University of Technology in Gothenburg, Sweden.

However, Kym Jarvis, an environmental geochemist at Kingston University in Kingston upon Thames, and her colleagues have discovered that palladium is soluble in a dilute acid solution. 'The high solubility of palladium suggests that, once it reaches the road surface, it would be in a form that can be more readily absorbed by vegetation, or which can go into the watercourse," she says. Both Jarvis's and Barbante's findings will appear in future issues of the journal Environmental Science and Technology. Ann Ananthaswamy

Twisted heart New Scientist 10 Feb 2001

The Milky Way's centre may be criss-crossed by cosmic rubber bands

THE long thin structures cutting across the centre of our Galaxy have been puzzling astronomers ever since they were discovered 17 years ago. Now, two Australian researchers suggest that the longest of these radio-emitting filaments, the Snake, is in fact a magnetic tube 200 light years long and twisted into two loops. Such twisted filaments may help explain how stars form in some molecular clouds.

In a paper that will be published in Astrophysical loumal Letters, Geoff Bicknell and jianke Li of the Australian National University in Canberra describe how the two kinks in the Snake, where radio emission is especially bright, were a crucial clue to its nature. According to the researchers' theoretical model, the Snake is a giant magnetic flux tube, a bundle of magnetic field lines drawn out into a thin strand, and the kinks are loops in the tube. They say the loops formed because the Snake's ends are anchored in rotating molecular clouds, which twist the tube until it doubles back on itself, like the knots that appear in a twisted rubber band. Where the loop crosses back on itself, the magnetic fields short-circuit, annihilating part of the field and releasing energy that accelerates nearby electrons close to the speed of light. As the electrons spiral round the magnetic field they emit radio waves, just as particles accelerated in a synchrotron here on Earth emit radiation. This explains why the Snake's kinks are so bright.

The flux tube model could explain some of the finer features of the Snake's radio emission. For example, the proportion of high-frequency radio emissions increases the further you get from the kinks. That makes sense, says Bicknell. High-speed electrons cause high-frequency emissions, and the faster ones diffuse more quickly away from the kink.

"It's a pretty detailed model. It's a big step forward," says Miller Goss, director of the Very Large Array radio telescope in New Mexico, and one of the co-discoverers of the Snake.

But not everyone is totally convinced by the new model. At least one end of the Snake is associated with a molecular cloud, says Cornelia Lang of the University of Massachusetts in Amherst, "but more detailed images of the Snake are necessary to confirm that it is twisted". Lang is working on just such a map of the Snake's magnetic field, and expects to finish it by April. Filaments have so far only been found at the centre of the Galaxy, and although their role is still far from clear, Bicknell speculates that they may play a key role in star formation. To make a star, a molecular cloud must contract and shed angular momentum. A twisted flux tube might draw off angular momentum very effectively, says Bicknell. Rachet Nowak, Metbourne

Flowers like nothing you've seen before
New Scientist 10 Feb 2001

MONSTER plants that are all flower and no leaf could soon be with us, now biologists have discovered how to make plants grow petals In place of leaves. As long ago as :L790, the German philosopher and playwright Johann Wolfgang von Goethe suggested that flower petals might be modified leaves. Over the past decade, biologists have uncovered three groups of genes that govern flower formation. If these genes are disabled, all the flower's petals, stamens and carpels are turned into leaf-like sepals.

But the reverse exercise of activating these genes failed to turn them into petals. Then last year researchers from the National Autonomous University of Mexico and the University of California at San Diego discovered three more 'flower' genes they named SEPALLATA. When the genes are disabled, the flowers also form only sepals (Nature, vol 405, p 200). 'Double flowers" with this mutation (above) have long been prized by gardeners, but the genetic basis was unknown. Now the same team has shown that by activating two of the SEPALLATA genes along with the three original groups of genes, they can create petals In place of leaves in the cress Arabidopsis (Current Biology, vol ii., p 182). Researchers at Kyoto University have come up with similar results (Nature, vot 409, p 525). Being able to produce petals in leaves is a fairly big deal.It tells us there aren't any other essential genes. The new discovery could allow growers to create, new kinds of flowers, such as roses with petals all along the stem. 'We should be able to do this in any plant, and any leaf Into a petal,' says Martin Yanofsky, a member of the San Diego team. Kurt Kleiner

Pheromones and MHCs New Scientist 10 Feb 2001

IT ALL started with a bit of harmless T-shirt sniffing. A group of women were asked to sniff T-shirts that had been worn by a group of unknown-and unwashed-men. All they had to do was say which shirts smelled best. The experiment, run by Claus Wedekind, a young Swiss scientist then at the University of Bern, was designed to find out if humans, like mice, use body odour to identify genetically appropriate mates. But it revealed something more worrying. As Wedekind predicted, most female volunteers had equivalent preferences to their rodent counterparts. Numerous studies in mice have shown that, given the choice, they sniff out mates with genes for immunity that differ from their own, and that this seems to increase their chances of producing healthy offspring. But among Wedekind's volunteers there was a startling exception to this trend. Women on the contraceptive pill showed the reverse preference. Instead of being attracted to the scent of dissimilar men, they chose men whose genes for immunity were closest to their own.

If humans are using smell to find a good partner for reproduction, and the Pill is turning things upside down, then there could be serious consequences. By tricking users into falling for the wrong guy, the Pill could be giving women better protection than they bargained for-making it harder for them to have kids long after they stop taking it. It's a contentious idea. For a start, not everyone agrees that the human brain can register such smells, let alone that they might influence our behaviour. But if they do, then does the Pill interfere with this form of sexual chemistry? "It's a reasonable question," says Wayne Potts, a biologist at the University of Utah in Salt Lake City, who specialises in mate choice. His colleague, Dustin Penn, goes further: "It wouldn't surprise me if sabotaging our reproductive machinery would lead to faulty mate choice. "

The genes at the centre of the debate are a large cluster called the major histocompatibility complex, or MHC. Each person has a unique combination of MHC genes that encode various components of their immune system. These include genes for histocompatibility antigens-which determine, for instance, whether your body will reject a foreign tissue graft-and for proteins called complements, which help fight off disease. The idea is that the more varied an individual's MHC, the more robust their immunity. And if your parents have widely varying MHC genes, your own MHC is more likely to be diverse. Parental differences may even increase the chances of your being born in the first place. Kunio Yamazaki at the Monell Chemical Senses Center in Philadelphia has found that mouse embryos conceived by parents with dissimilar MHCs are more likely to make it to term. And at the Reproductive Science Center of the Bay Area in San Ramon, California, Louis Weckstein found that human couples who fail to conceive after two Or more attempts with IVF shared significantly more MHC genes than successful IVF couples. If olfactory cues about MHC genes are so important, why do women taking the Pill seem to respond so differently from other women? 'My guess is that the Pill simulates pregnancy and that maybe during pregnancy, odour preferences change,' says Wedekind. This appears to be what happens in mice, he points out. The theory is that during pregnancy, a female is attracted to the smell of her own relatives, who have similar MHCs to her own. After all, family members have the greatest interest in seeing her offspring survive. Pregnant womenand women whose bodies are tricked into thinking they're pregnant-might have the same tendency, says Wedekind. The implications are not lost on Marian Petrie from the University of Newcastle upon Tyne. 'Potentially, women might affect their chances of becoming [pregnant], not by something that's an obvious means," she says. "It might be important generally to infertility problems." In the next few months, she and her colleague Craig Roberts will run a follow-up to Wedekind's study to find out whether the Pill really does skew women's smell preference. They will ask 80 women who are planning to start taking oral contraceptives to do the T-shirt test, both before and a few months after they go on the Pill. The researchers will also run the same test on 80 women trying to get pregnant, both before and after conception. To date, almost all the work on MHC differences, mate choice and their effects on offspring viability has been done on rodents. But geneticist Carole Ober from the University of Chicago has come up with a cunning way to explore some of the same questions in humans. For over a decade, she has been studying a North American religious community known as the Hutterites. Following Wedekind's revelations about the women's preference for certain odours in an artificial laboratory setting, Ober aimed to get information about real partnerships. In many ways, Hutterites are the perfect study group for "natural" mate choice among humans. They are a socially isolated group who work on communal farms, marry within their own community, and can trace their roots back to a handful of European ancestors in the 16th century. Single men and women visit neighbouring Hutterite colonies, and often end up working or celebrating special occasions alongside potential spouses. They don't use perfumes or deodorants. "They are absolutely maximising the importance of MHC, " says Ober. They marry once-divorce is strictly prohibited-and, claims Ober, they marry for love. Once paired off, they place a high value on big families, and seldom use contraception.

So do Hutterites tend to marry people who have dissimilar MHCS? To answer this question, Ober and her colleagues studied 411 couples drawn from 31 Hutterite colonies.

They made two separate calculations of how many couples would end up matching for certain haplotypes, or 'linked" MHC genes found close together on chromosome 6, if there was no active avoidance of mates with similar MHCS.

In the first, they predicted how many Hutterite couples with similar MHCs would just happen to end up together, having taken into account factors such as the way women always move to their husband's colony after marriage, that Hutterites never marry first cousins and that siblings often marry into the same family. In the second, they used the exact genealogy of each of the volunteers to establish that there would have been between 60 and 80 unrelated "ancestral" haplotypes for this particular chromosome among their founding ancestors. They then ran a computer simulation based on this genealogy to see how many couples with similar MHCs you would expect to find if Hutterites married at random.

Next, the researchers compared these calculations with the actual situation. As they had suspected, the Hufterite men and women they studied tended to avoid pairing off with mates who had similar MHC genes to their own. Despite the lack of genetic variation within this isolated population, only 44 of the couples matched for any haplotypesignificantly fewer than the 65 predicted from the first calculation. The genealogy study backed that up: if mate selection were random the probability that only 44 couples would have matched was only about 5 per cent. Ober's group concludes that genes in this region of DNA may indeed influence mate choice in humans.

The findings were published in 1997, along with a review by Yamazaki and his colleague Gary Beauchamp, director of Monell, who were delighted that at last there was some evidence in humans for the effect they had found in rodents. Their enthusiasm was dampened, however, by results from another excellent study published alongside Ober's paper, which had examined the same question and come to a different conclusion. Philip Hedrick of Arizona State University in Tempe and Francis Black at Yale University studied 194 couples from Amazonian Indian tribes and found that people seemed to pair off randomly. Yamazaki and Beauchamp suggested that the large number of Hutterite couples studied and the special characteristics of the culture may have made this group better than the Amazonian tribes for detecting a small but real effect.

The next question for Ober was whether couples with similar MHCs actually have reduced fertility. Some of her early research on Hutterites had hinted that couples who had a large number of MHC matches took longer to conceive. She decided to look at this effect more carefully, asking 111 Hutterite women to keep diaries recording all their menstrual periods. If they didn't have a period on the day expected, the women took a pregnancy test and recorded the result. The women were also asked to note whether they were nursing other infants, practising birth control of any kind or were ill-any of which could affect the likelihood of conception. During the course of the study-the first to examine possible links between MHC and miscarriage in humans-she collected information on 251 pregnancies.

Of the 111 women, 27 had miscarriages, and there were 38 miscarriages altogether. None of the couples was completely infertile-all but one had already had at least one child, and none had more than two consecutive miscarriages. But when Ober scrutinised the MHC genes from the women and their husbands at 16 separate genetic sites, she found that miscarriage rates were highest for couples who matched at all these sites. And there was an increased risk even where there was matching at just some of the sites.

"The effects we see in the Hutterites are pretty clear," says Ober. But she adds that Hutterites are an isolated population, and they have a limited repertoire of certain MHC genes. "At this point, it's difficult to say whether the same is true of out-bred couples,' she says. A Hutterite couple is much more likely to have matching DNA at these particular miscarriage black spots than a couple who do not live in a genetically isolated community. Even so, Ober believes that the actual risks associated with having one or two such genetic matches could be similar in any population.

The fertility gods may well frown on couples with similar MHCS. But where does all this leave Pill users? Even if using oral contraceptives alters a woman's sense of smell, does smell itself really play such a big part in choosing a man? The effect may be subtle and subconscious, argues Penn, but that doesn't mean smell is unimportant. He points out that chemosensory signals are used to attract and select mates in many species, from bacteria to plants to mice. "What we know about mate choice in other species tells us they use lots of different information," he says. 'They use everything-everything they can." Studies in female rodents have shown that the scent of a male can sometimes speed up puberty, activate ovulation and even induce miscarriage. Humans also use odour cues in at least some matters related to reproduction. For instance, Martha McClintock at the University of Chicago showed in 1998 that when women who live together synchronise their menstrual cycles, they do it through chemical signals known as pheromones. McClintock has recently teamed up with Ober to further explore the impact of the Pill on chemical communication. As far as anyone can tell, whatever chemical signals do pass between people are subconscious. Nonetheless, Rachel Herz from Brown University in Providence, Rhode Island, decided to ask people about it directly. She polled 166 women about what makes a man attractive-specifically, attractive enough to go to bed with. Out of a variety of factors, including appearance, the sound of his voice and how his skin feels, women respondents said that a man's scent was paramount. Body odour was particularly important, the volunteers reported, in decisions not to have sex with a certain individual. The question is not whether there are human MHC smells-that is more or less resolved. Rats in the labs of Beauchamps and Yamazaki are able to distinguish between people with different MHC types simply by sniffing their urine. This is strong evidence, the researchers say, that MHC genes influence body odour in humans just as they do in rodents. The genes may affect the concentrations of volatile acids in body fluids, such as urine, blood, breast milk or even sweat. These in turn could act as sexual odorants.

The real question is, even if these odours are advertising what kind of MHC a person has, do humans still have the capacity to pick up the scent and act on it? Rodents have something called a vomeronasal organ (VNO)-a region high in the nose that can detect chemosensory signals. That system bypasses conscious centres of the brain and has direct access to the amygdala and hypothalamus, which govern sexual behaviour. In most animals with a VNO, reproductive behaviour is disrupted if you cut this part of the nose out. There is still a debate raging about whether humans even have a VNO (New Scientist, 25 January 1997, p 36). We do seem to have a structure similar to a VNO during early development, but there is no strong evidence that the vestige that remains into adulthood is functional. Maybe we don't need one. Pigs, rabbits and sheep have a VNO, but detect some pheromones through their main olfactory system. It's possible that humans do too. After all, a functioning human pheromone receptor gene was identified last year (New Scientist, 2 September 2000, p 7). And proponents point out that humans have more scent glands than any other mammal. What for, if not to communicate? But there is still no consensus on whether humans have some kind of working chemosensory perception or just remnants ftom a once-elaborate system that evolution decided to phase out. Still, Hutterites do tend to marry those with different MHCS. And women did respond differently to a sniff ftom those T-shirts when they were on the Pill. So it's not inconceivable that the Pill is meddling with whatever chemosensory perception we have. 'It makes sense that if you change the hormonal environment, you change olfaction," says Ober.

At first glance, the Pill's glittering record should be enough to quash the whole discussion. Oral contraception has been in use since 1960, and there is no evidence so far that women who have taken the Pill have lower fertility when they stop. Several large studies looking at tens of thousands of women have been reassuring, says Martin Vessey, an epidemiologist at the University of Oxford. "Studies haven't suggested an association between fetal loss and Pill use," he says. But then, no study has looked specifically at women who found life partners while on the Pill, he admits. And it's only recently that women have been using the contraceptive pill from such a young age-sometimes from before their first sexual encounter straight through to the time when they want to have kids.

Then there's the fact that the Pill has so far been the darling of the developed world, where there are relatively few challenges to the immune system. Would its impact on fertility be more readily seen if women in the developing world took a shine to it? 'There it might matter," says Wedekind. He cautions, however, that no research has been done in this area. 'I think it's worth investigating,' 4e adds. Clearly pathogens do affect mate choice in animals. Research by Wedekind and Thomas Rftlicke of University Hospital Zurich shows that when mouse colonies are infected with a mouse hepatitis virus, their offspring have more varied MHCS. The researchers believe this is partly due to the egg selecting specific sperm to maximise the survival chances of the resulting offspring.

Despite this, no self-respecting woman of the 21st century would want to disparage the Pill. For the past 40 years it has liberated us from the threat of unwanted pregnancy, leaving us free to earn degrees, climb corporate ladders and travel the world, all without having to swear off sex. Even so, it might be worth taking precautions. Herz suggests that if you are on the Pill and meet someone you want to have children with, you should stop taking oral contraceptives. 'Go off," she says, "to see if you're still attracted.

Further reading: "MHC-dependent mate preference in humans" by Claus Wedekind and others, Proceedings of the Royal Society B, vot 260, p 245 (1995) "HLA and human mate choice" by Carole Ober and others, American Journal of Human Genetics, vot 61, p 49T (1997) "Differential use of sensory information in sexual behaviour as a function of gender" by Rachet Herz and others, Human Nature, vot 8, p 275 (1997) "MHC-genotype of progeny influenced by parental infection" by Thomas Rolicke and others, Proceedings of the Royal Society B, vot 265, p 711 (1998)

Tuesday, 15 May, 2001, 22:32 GMT 23:32 UK Amazon destruction surges

Up to 40% of the rainforest could be cleared within 20 years The destruction of Brazil's Amazon rainforest jumped to a five-year high last year, alarming environmentalists and embarrassing the Brazilian Government.

The government had hoped that forest clearance was decreasing, but satellite images analysed by its Space Research Institute reveal that between 1999 and 2000, almost 20,000 sq km were cleared.

This creates a hole about the size of Belgium, and is a 15% increase on the previous year.

The secretary for Amazon affairs for the Environmental Ministry, Mary Allegretti, blamed the increased deforestation on an improved economic climate.

Demand for land

An unexpectedly healthy recovery from Brazil's recession, following the devaluation of its currency in January 1999, sparked more demand for timber and land.

Ms Allegretti said the rain forest was cut down by logging companies and farmers in search of land.

Independent research institutes forecast that if the government continues with its road building and farming programmes in the Amazon region, up to 40% of the total rainforest will be destroyed within 20 years.

Environmentalists say action needs to be taken to reverse the unsustainable destruction of the Amazon, which is home to up to 30% of the world's animal and plant life.

"The beginning of the new millennium could not have been worse for the Amazon, the figures are worrying if we look to the future," said the World Wildlife Fund in a statement.

Ms Allergen said the government would introduce a licensing system for properties where deforestation was worst.

Government action

But our correspondent Jan Rocha says that within the next two weeks a controversial bill which would allow Amazon farmers to legally clear much greater areas of forest will be debated in Congress.

The bill is supported by farmers and opposed by environmentalists, she says.

The government is also considering building more energy plants in the area, as the country is suffering from a chronic energy shortage.

In 1970, about 99% of the Amazon, which is sometimes termed the "lungs of the planet", due to the huge amounts of oxygen produced by its trees, was still standing.

Thursday, 19 April, 2001, 23:02 GMT 00:02 UK Breakthrough in 'superbug' battle

The genetic structure of the bacterium was decoded Japanese researchers have published the completed genomes of two antibiotic resistant strains of one of the world's most dangerous bacteria.

Staphylococcus aureus is the bug responsible for many hospital infections, and scientists are worried that some strains were acquiring high levels of resistance to virtually every available antibiotic.

The team from Juntendo University in Tokyo is the first to publish a complete guide to its entire genetic structure.

Now scientists can begin the long process of finding possible genetic targets for new vaccines and drugs.

Both of the strains are typed according to their resistance to antibiotics commonly used to treat them.

One of the sequenced strains is Methicillin-resistant (MRSA).

This so-called "superbug" is proving difficult to eradicate from UK hospitals because it is resistant to all but a few antibiotics.

The other is a Vancomycin-resistant strain, which is considered even more dangerous.

This has managed to mutate to resist even the antibiotic described as the "last line of defence" against such staph infections.

The scientists found many sections of the bug's DNA seemed to have been acquired from other organisms - some may even have come from humans.

This gives a clue as to how the bacterium has proved so successful in adapting to its environment and resisting drug treatments.

'Exciting breakthrough'

Dr Nick Day, a consultant in infectious disease at John Radcliffe Hospital in Oxford, and a Wellcome Trust Fellow, is himself working to discover potential therapy or vaccine targets in the genetic structure of Staphylococcus aureus.

He said: "This is very exciting news - it's a real landmark finding.

"By identifying all the genes, we can find new genes which may actually be major disease-causing genes."

The Japanese team has beaten competition from the Sanger Centre in the UK and another centre in the US to produce the first complete Staphylococcus Aureus genome.

Many other disease-causing bacteria have been fully sequenced and the genetic information published for scientists to use.

One study has estimated that hospital-acquired infections, such as MRSA or even normal MSSA - the non-resistant form - cost the NHS £3bn a year in extra treatment and time spent in hospital.

The government has ordered hospitals to improve hygiene standards in an effort to cut the number of infections.

Details of the genomes have been published in the Lancet medical journal.