A notorious Alzheimer’s disease villain may also be a germ-busting superhero. Amyloid-beta gums up the brains of people with Alzheimer’s but also takes out dangerous brain invaders, scientists report May 25 in Science Translational Medicine.

As strong as steel, tough strands of A-beta protein imprison pathogens that threaten the body and brain, experiments in mice and worms show. Those results raise the possibility that A-beta plays a role in the immune system and its accumulation in Alzheimer’s might be prompted by an infection.
Earlier studies have shown that A-beta can bust germs in cells in dishes, but the new experiment shows A-beta protection in living mice and worms. Mice engineered to have the human form of A-beta better survived a brain infection of Salmonella bacteria than mice without the human A-beta, Robert Moir and Rudolph Tanzi, both of Harvard Medical School, and colleagues found. And in the bodies of worms, A-beta helped stave off the dangerous yeast Candida.

When researchers injected Salmonella into mice’s hippocampi, a brain area damaged in Alzheimer’s, A-beta quickly sprang into action. It swarmed the bugs and formed aggregates called fibrils and plaques. “Overnight you see the plaques throughout the hippocampus where the bugs were, and then in each single plaque is a single bacterium,” Tanzi says. That rapid response was surprising, he says. “No one expected that.”
And those prisons are probably permanent, Moir says. “In A-beta, those fibrils set like concrete and the bugs have no chance of ever getting out.”

Alzheimer’s has been linked to a host of bacterial, fungal and viral infections, says immunologist Kevan Hartshorn of Boston University School of Medicine. That work, along with the new study, raises the possibility that Alzheimer’s could be spurred by an immune response to a pathogen.

That’s “an extremely provocative and interesting hypothesis,” says neuroscientist Berislav Zlokovic of the University of Southern California in Los Angeles, who says the new data are convincing. But it remains to be seen whether the results are relevant for people with Alzheimer’s. Zlokovic and colleagues recently found that the barrier between brain and blood weakens with age — a situation that could let more microbes into the brain and perhaps spur A-beta accumulation.
A-beta appears to be a general immune system fighter that’s effective against many enemies, says Moir. “This is a classical innate immune response, which means that whatever gets thrown at it, it does the same thing,” he says. “So whether it’s a herpesvirus, a spirochete or chlamydia, it’s going to generate A-beta plaques.”

Moir also raises the possibility that the amyloid’s germ-busting job might play a role in other diseases that come with amyloid accumulation, such as diabetes or heart disease. “I think we may have stumbled across an underlying theme in a lot of major diseases,” he says.

Finding this helpful role for A-beta may complicate a therapeutic approach for Alzheimer’s that attempts to reduce levels of the protein with antibodies, says molecular pharmacologist Marina Ziche of the University of Siena in Italy. “I have always been very skeptical about that approach,” and the new results suggest that people benefit from some A-beta, Ziche says.

The next step is to see whether pathogens are entombed in A-beta plaques in the human brain, Tanzi says. “Now it’s time to start looking for them in patients.” To start, he and colleagues have just begun a project to catalog the collection of microbes in healthy brains and brains with Alzheimer’s.

Finding a strong link between pathogens and Alzheimer’s could suggest new ways to prevent the disease, Tanzi says. Vaccines that fight infections, for instance, might be one way to prevent A-beta pileup.

Two more of the ingredients for life as we know it have turned up in space, this time from a comet orbiting the sun. While hints of both have been seen in comets before, this is the clearest evidence to date.

Glycine, the smallest of the 20 amino acids that build proteins, is floating in the tenuous atmosphere of comet 67P/Churyumov-Gerasimenko, researchers report online May 27 in Science Advances. Comet 67P’s atmosphere also holds phosphorus, which is essential to DNA and RNA. Both detections support the idea that comets are at least partly responsible for seeding early Earth with material needed for life.
The phosphorus, glycine and a handful of other organic molecules were detected by the European Space Agency’s Rosetta spacecraft, which has been in orbit around 67P since August 2014 (SN: 9/6/14, p. 8). Kathrin Altwegg, a planetary scientist at the University of Bern in Switzerland, led the study.

Previous searches for glycine in comets Hale-Bopp and C/1996 B2 (Hyakutake) turned up nothing. Glycine was seen in samples from the Stardust mission, which flew through the tail of comet Wild 2 in 2004 and brought comet dust back to Earth, but those measurements were complicated by lab contamination. Scientists have detected hints of phosphorus in comet Halley.

Life’s ingredients keep turning up in cosmic environments. Meteorites carry amino acids and simple sugars have been seen in interstellar clouds(SN: 10/9/04, p. 237). And several of the essential molecules for DNA and RNA, such as ribose, have been created in laboratory experiments that simulate ice grains exposed to ultraviolet radiation from young stars (SN: 4/30/16, p. 18).

Giant squid are the stuff of nightmares. They were even one of the deadly dangers in Jules Verne’s 20,000 Leagues Under the Sea, attacking the Nautilus in a group and carrying off one of the crew:

Just as we were crowding each other to reach the platform, two more arms lashed the air, swooped on the seaman stationed in front of Captain Nemo, and carried the fellow away with irresistible violence…. What a scene! Seized by the tentacle and glued to its suckers, the unfortunate man was swinging in the air at the mercy of this enormous appendage. He gasped, he choked, he yelled: ‘Help! Help!’ … The poor fellow was done for.

What makes Verne’s giant squid all the more frightening is that he didn’t invent the creatures; giant squid strandings had been documented in Europe since at least 1639, and scientists informally described the animals in the late 1850s.

But even if we don’t really have to worry about the huge invertebrates snatching people off boats, giant squid remain mysterious. They weren’t even photographed in the wild until 2004. And many questions remain unanswered about them. The biggest: Just how giant can the giants get? A new study has come up with an estimate — and also highlights the many reasons why it’s so difficult to come up with one.

Charles Paxton of the University of St. Andrews in Scotland starts by laying out five ways that it should be possible to estimate squid length, and why the first four aren’t great measures. Anecdotal accounts — which claim giant squid reaching lengths of 30 meters and 53 meters, not counting the two long tentacles — are often riddled with inaccuracy and exaggeration. Estimating maximum length based on squid growth rate won’t work because squid growth rates just aren’t well known. Some scientists have tried to determine lengths based on the sucker scars found on whales, but since scientists don’t know how whale growth affects the sizes of those scars, those aren’t a good measure either.

Direct measurement of dead squid would seem to be a good option, except that the two long tentacles of a squid — which extend far beyond the animal’s arms and determine its full length — are elastic and can change in length when a squid is preserved, Paxton notes. That leaves the fifth method — estimating length based on the size of the hard beak. Beak size and squid body length are related.

Paxton combined the last two methods to come up with a maximum length for a giant squid of about 20 meters, from the top of its mantle, or body, to the tip of its long tentacles. His estimate appears May 17 in the Journal of Zoology.
The longest squid ever reported was 17.37 meters long, and Paxton questions its veracity, as does another paper published last year in PeerJ. Craig McClain of Duke University and colleagues note that the “longest scientifically verified giant squid” measured a mere 12 meters. “What limits the large size of [giant squid] is unclear,” McClain and colleagues write. But metabolic demands may play a role, keeping squid from getting much bigger than what have washed up onto shore (and also keeping them in the cold depths where they’re so difficult for us to find).

But perhaps the focus on the largest and biggest of species is the wrong approach, McClain and his colleagues argue (in, ironically, a paper all about large marine species). The longest, most giant individuals are, after all, just a tiny fraction of a species — and, these researchers write, “these individuals may reach these extraordinary large sizes through developmental or genetic defects and may not represent the healthiest or, in evolutionary terms, the fittest.”

They are, though, among the most mysterious creatures to inhabit our planet.

From California to China, desert moss (Syntrichia caninervis) braves life in hot deserts and still stays hydrated. What’s its secret? The moss gathers water via a topsy-turvy collection system in its leaves.

Moss leaves have tiny hairlike points at their ends called awns. Previous evidence pointed to a potential role for the awns in water collection and prompted Tadd Truscott of Utah State University and his colleagues to zero in on the structures.

Imaging exposed a system of barbs that line the awns and catch tiny airborne water droplets, the team reports June 6 in Nature Plants. When the air is misty, foggy or the least bit humid, trapped dewdrops move up grooves in the moss leaves by capillary action. The tiny drops form a bigger drop to be absorbed and stored by the plant. When it rains, moss awns reduce splash and capture raindrops by the same mechanism.

Most desert plants, especially cacti, get their water from roots, but moss may not be the only plant that uses unique leaf structures to stock up on water, the team argues.