9 February 2013 | NewScientist | 19

Extreme life can colour rocky worlds

LICHENS and algae could be the first life forms we find on Earth-like exoplanets, by looking for their light signatures in a planet’s distinctive colouring.

Seen from space, Earth gives off a large amount of near-infrared light, which is reflecting off the chlorophyll in plants. As telescopes get more sensitive, it should be possible to see a similar “red edge” on distant exoplanets if they also host green vegetation.

But Siddharth Hegde and Lisa Kaltenegger of the Max Planck Institute for Astronomy in Heidelberg, Germany, think it is possible that many rocky worlds will have extreme heat, dryness or acidity, and that hardier life forms will dominate their surfaces. So what would these organisms look like from a distance?

To find out the pair looked at the light reflected by some of Earth’s more extreme life forms: lichens in arid regions, bacterial mats in very hot water and red algae in acid mine drainage. They calculated that seen from afar each type of organism would create a unique colour pattern. Lichens, for instance, appear more yellow than the algae or bacteria (Astrobiology, doi.org/kch).

Stomach this… faecal transplants reveal gut bug menaceMALNUTRITION isn’t just down to a poor diet or lack of food – gut bugs may play a part too.

It has been unclear why some children are prone to malnourishment when siblings fare better. To investigate, Jeffrey Gordon at Washington University in St Louis, Missouri, and his colleagues travelled to Malawi to find sets of twins in which one child had a severe form of malnutrition called kwashiorkor while the other did not, despite shared genetics and a similar diet.

The team took faecal samples

from three pairs of twins and transplanted them into the guts of mice, which were fed a nutrient-poor Malawian diet.

All of the mice lost some weight, but some lost significantly more than others – and faster. These mice had all received a faecal sample from the children with kwashiorkor.

Analysis of the rodents’ gut flora revealed high levels of bacteria associated with illnesses such as inflammatory bowel disease (Science, doi.org/kct).

Particular bugs may restrict

IT LIKES a blowout, in more ways than one. When attacked, the giant California sea cucumber (Parastichopus californicus) has an explosive escape strategy: it squirts its digestive system out of its anus in a sticky mess to confuse its foe. That’s all well and good, but surely it can’t survive without its guts? Not true: to get by, it eats through its anus.

The sea cucumber’s anatomy is a little peculiar. Its respiratory system is connected to its anus, through which it sucks water to take in dissolved oxygen. When Richard Strathmann of the University of Washington in

Friday Harbor added algae containing radioactive carbon-14 to the creature’s environment, he found that carbon-14 ended up in the respiratory system. That suggests the sea cucumber can take in algae through its anus as well as its mouth (Invertebrate Biology, doi.org/kcm).

It’s not clear how the respiratory system digests the algae, or why anal feeding evolved. Strathmann says it could have begun as a way to pick up extra food from the surrounding water. “Nutrition through the anus is a remarkable reversal of what we expect,” he says.

Meet the ultimate bottom feeder

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calorie availability and exacerbate a poor diet, says co-author Jeremy Nicholson at Imperial College London.

A second study led by Indi Trehan, another member of the team at Washington University, showed that children with kwashiorkor were less likely to become malnourished again if they were given antibiotics along with a nutrient-rich diet (NEJM, doi.org/kc4). This might mean that, in the future, microbial concoctions can be tailored to treat such conditions, says Nicholson.

Provoking fear in the fearless

“AM” thought she was dying. Moments after taking a deep breath through the mask that had been voluntarily placed over her nose and mouth she lifted her arms in panic. It was the first time in her life she had experienced fear.

This came as a quite a shock to researcher Justin Feinstein, now at the California Institute of Technology in Pasadena. That’s because AM has Urbach–Wiethe disease, which has, until now, made her fearless due to the destruction of a part of her brain called the amygdala. The result challenges the widely held belief that the amygdala is essential for fear.

Feinstein managed to scare AM by exposing her to carbon dioxide levels of 35 per cent. The technique also provoked intense fear in two other volunteers with the same condition (Nature Neuroscience, DOI: 10.1038/nn.3323).

Interestingly, unlike most people, whose heart rates rise prior to a repeat of the carbon-dioxide experiment, AM and her cohorts never developed an anticipatory response. They could feel fear but not anticipate it.

Carbon dioxide changes blood acidity, activating acid-activated chemical receptors in the brain. This study hints that internal threats are processed differently by the brain than external ones, says Feinstein.

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130209_N_p18_19_IB.indd 19 4/2/13 17:00:26