Spiders' sticky silk has a dual identity

Spiders' sticky silk has a dual identity

For new stories every day, visit newscientist.com/news Andrew Tomkins FEW things seem more ephemeral than shooting stars. Yet the scorched remains o...

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Andrew Tomkins

FEW things seem more ephemeral than shooting stars. Yet the scorched remains of 60 micrometeorites have survived 2.7 billion years in the limestone Tumbiana Formation of Western Australia. They are some of the oldest space rocks ever discovered on Earth. The fact that the meteorites contain oxides of iron also shows that the upper atmosphere must have contained oxygen at least 300 million years earlier than ground-level air. “We were very surprised to find micrometeorites at all, let alone those with iron oxides,” says Matthew Genge of Imperial College London. “These tiny spherules had trapped ancient atmosphere, storing it away like little treasure chests.” The presence of oxygen in the meteorites means that levels of this gas in the upper atmosphere, 75 kilometres high, at the time must have been similar to levels found in the atmosphere today – roughly 20 per cent (Nature, doi.org/bhgs). That oxygen might have come from the sun’s ultraviolet radiation splitting molecules such as water and sulphur dioxide, thus freeing oxygen at high altitudes. The team thinks a methane-rich layer in the middle atmosphere would have separated the bulk of anoxic air below from the oxygen-rich upper atmosphere.

Life’s origin not so tough if you can build bits of RNA in the lab ONE of the hardest steps leading up to life on Earth might not be so hard after all. RNA, or something very like it, has long been a strong candidate for the first self-replicating molecule necessary for life. It carries genetic information and can also catalyse many biochemical reactions. But how could a large, complex molecule like RNA form spontaneously? The main sticking point was that no one knew of a plausible way to make two components of it, adenosine and

guanosine – needed to represent A and G in the genetic code. Making these subunits separately and linking them together step by step generally led to a useless mess in which most of the molecules were the wrong shape. Now a team led by Thomas Carell, an organic chemist at the Ludwig Maximilians University in Munich, Germany, may have cracked it. They started with simpler precursor chemicals and let the whole process unfold at once, under mildly acidic conditions that

mimicked those of early Earth. Their approach produced high yields of adenosine, and some guanosine (Science, DOI: doi.org/ bhgv). Better yet, Carell’s starting points – such as formic acid – or their precursors have been found on comets and thus were probably available at the origin of life. “We now have a pathway that would allow us to use simple molecules that were likely present on the early Earth,” says Carell. The next step is to link the components into a full-length RNA strand, he says. Stefan Sollfors / Alamy Stock Photo

Shooting stars’ oxygen mystery

Spiders’ sticky silk has a dual identity SPIDER silk acts as both a liquid and a solid, a feat that could inspire new types of robots. Arnaud Antkowiak of the Pierre and Marie Curie University in Paris, France, and his colleagues studied the sticky “capture silk” that makes up the spiral of an orb-weaver spider’s web. When stretched, the silk extends like a spring. But when compressed, it remains taut, rather than sagging in the middle as an ordinary thread might. Most materials that act like this are liquids: a soap film is an example. “It seems to adapt its length,” says Antkowiak. The capture silk appears to be a liquid-solid hybrid that changes its size according to the space it needs to fill. “It’s just weird,” he says. This dual nature stems from the silk being made of a filament wrapped in glue droplets. The team was able to mimic this behaviour with a range of plastic filaments coated in silicone oil, ethanol or other liquids, creating what they call “liquid wires” (PNAS, DOI: 10.1073/pnas.1602451113). Antkowiak says this behaviour could make the materials useful in building soft robots.

Time for a new dandruff shampoo? LOOKS like our knowledge was a little flaky. It seems bacteria, rather than fungi, could determine whether you get dandruff. Since the 19th century, the prevailing wisdom has been that a fungus called Malassezia is to blame for dandruff. But now we have bacteria in the cross hairs. Zhijue Xu of Shanghai Jiao Tong University in China and his team swabbed the scalps of 363 adults, and used DNA sequencing to compare their fungi and bacteria. They found that about 90 per cent of scalp fungus in all people, regardless

of whether or not they had dandruff, was Malassezia restricta. But bacteria revealed a different story. People with dandruff had more Staphylococcus bacteria and much less Propionibacterium than those who didn’t have dandruff, suggesting that the bacterial balance on your head may determine whether you sport snowy flakes in your coiffure (Scientific Reports, doi.org/bhgq). Xu says his team will now investigate methods for balancing the proportions of scalp bacteria, which they hope might be a way to reduce dandruff.

21 May 2016 | NewScientist | 15